<PAGE>   1
 
================================================================================
 
                                 UNITED STATES
                       SECURITIES AND EXCHANGE COMMISSION
                             WASHINGTON, D.C. 20549
 
                            ------------------------
 
   
                                  FORM 10-K/A
    
(MARK ONE)
 
     [X]   ANNUAL REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE
        SECURITIES EXCHANGE ACT OF 1934
 
                  FOR THE FISCAL YEAR ENDED DECEMBER 31, 1997
 
                                       OR
 
     [ ]   TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(D) OF THE SECURITIES
           EXCHANGE ACT OF 1934
 
                         FOR THE TRANSITION PERIOD FROM
                               --------------- TO
                                ---------------
 
                        COMMISSION FILE NUMBER: 0-19311
 
                        IDEC PHARMACEUTICALS CORPORATION
              (EXACT NAME OF REGISTRANT SPECIFIED IN ITS CHARTER)
 

<TABLE>
<S>                                            <C>
                   DELAWARE                                           33-0112644
       (STATE OR OTHER JURISDICTION OF                             (I.R.S. EMPLOYER
        INCORPORATION OR ORGANIZATION)                           IDENTIFICATION NO.)
</TABLE>

 
               11011 TORREYANA ROAD, SAN DIEGO, CALIFORNIA 92121
             (ADDRESS OF PRINCIPAL EXECUTIVE OFFICES)    (ZIP CODE)
 
                                 (619) 550-8500
              (REGISTRANT'S TELEPHONE NUMBER, INCLUDING AREA CODE)
 
          SECURITIES REGISTERED PURSUANT TO SECTION 12(b) OF THE ACT:
                                      NONE
 
          SECURITIES REGISTERED PURSUANT TO SECTION 12(g) OF THE ACT:
                         COMMON STOCK, $.001 PAR VALUE
                                (TITLE OF CLASS)
 
     Indicate by check mark whether the registrant (1) has filed all reports
required to be filed by Section 13 or 15(d) of the Securities Exchange Act of
1934 during the preceding 12 months (or for such shorter period that the
registrant was required to file such reports), and (2) has been subject to such
filing requirements for the past 90 days.  Yes [X] No [ ]
 
     Indicate by check mark if disclosure of delinquent filers pursuant to Item
405 of Regulation S-K is not contained herein, and will not be contained, to the
best of the registrant's knowledge, in the definitive proxy or information
statements incorporated by reference in Part III of this Form 10-K or any
amendment to this Form 10-K. [X]
 
     As of January 30, 1998, the aggregate market value of the voting stock held
by non-affiliates of the Registrant was approximately $778,371,000. (Based upon
the "closing" price as reported by the Nasdaq National Market on January 30,
1998). This number is provided only for the purposes of this report and does not
represent an admission by either the Registrant or any such person as to the
status of such person.
 
     As of January 30, 1998, the Registrant had 19,630,694 shares of its common
stock, $.001 par value, issued and outstanding.
 
                      DOCUMENTS INCORPORATED BY REFERENCE
 
     Portions of the Registrant's Proxy Statement for its Annual Meeting of
Stockholders to be held on May 21, 1998 are incorporated by reference into Part
III.
================================================================================

<PAGE>   2
 
                        IDEC PHARMACEUTICALS CORPORATION
 
                           ANNUAL REPORT ON FORM 10-K
 
                  FOR THE FISCAL YEAR ENDED DECEMBER 31, 1997
 
                               TABLE OF CONTENTS
 
   

<TABLE>
<S>       <C>                                                           <C>
Risk Factors..........................................................  1
 

                                  PART I:
 

Item 1.   Business....................................................  11

Item 2.   Properties..................................................  30

Item 3.   Legal Proceedings...........................................  30

Item 4.   Submission of Matters to a Vote of Stockholders.............  30
 

                                 PART II:
 

Item 5.   Market for Registrant's Common Equity and Related
          Stockholders Matters........................................  31

Item 6.   Selected Financial Data.....................................  32

Item 7.   Management's Discussion and Analysis of Financial Condition
          and Results of Operations...................................  33

Item 7A.  Quantitative and Qualitative Disclosures About Market
          Risk........................................................  37

Item 8.   Consolidated Financial Statements and Supplementary Data....  38

Item 9.   Changes in and Disagreements with Accountants on Accounting
          and Financial Disclosure....................................  55
 

                                 PART III:
 

Item 10.  Directors and Executive Officers of the Registrant..........  55

Item 11.  Executive Compensation......................................  58

Item 12.  Security Ownership of Certain Beneficial Owners and
          Management..................................................  59

Item 13.  Certain Relationships and Related Transactions..............  60
 

                                 PART IV:
 

Item 14.  Exhibits, Financial Statement Schedules, and Reports on Form
          8-K.........................................................  61
</TABLE>

    
 
                                        i

<PAGE>   3
 
     This Form 10-K contains predictions, estimates and other forward-looking
statements that involve a number of risks and uncertainties. While this outlook
represents our current judgment on the future direction of the business, such
risks and uncertainties could cause actual results to differ materially from any
future performance suggested below. IDEC Pharmaceuticals Corporation ("IDEC
Pharmaceuticals" or the "Company") undertakes no obligation to release publicly
the results of any revisions to these forward-looking statements to reflect
events or circumstances arising after the date hereof other than required by the
Securities and Exchange Act of 1934, as amended, or the rules and regulations
promulgated thereunder.
 
                                  RISK FACTORS
 
HISTORY OF OPERATING LOSSES; ACCUMULATED DEFICIT
 
     IDEC Pharmaceuticals(R) has incurred annual operating losses since its
inception in 1985 and may incur additional losses in the future. As of December
31, 1997, the Company's accumulated deficit was approximately $99.4 million.
Historical losses have been principally the result of the various costs
associated with the Company's research and development, clinical and
manufacturing activities prior to approval for marketing of any of the Company's
products. Substantially all revenues to date have resulted from collaborative
research, development and licensing arrangements, research grants and interest
income. There is no guarantee that the Company will achieve profitable
operations on an annual basis unless either Rituxan(TM) (as defined below)
achieves commercial success or product candidates now under development receive
approval from the U.S. Food and Drug Administration ("FDA") or foreign
regulatory bodies and thereafter are commercialized successfully.
 
     Rituxan, which received regulatory approval in the United States on
November 26, 1997 and in Switzerland on November 28, 1997, each for single agent
use in relapsed or refractory, low-grade or follicular, CD20 positive, B-cell
non-Hodgkin's lymphomas ("B-cell non-Hodgkin's lymphomas"), is the Company's
only approved product. Rituxan is the trade name in the United States for the
compound Rituximab (formerly known as IDEC-C2B8). In Switzerland, and upon
approval in the rest of Europe, Rituximab is marketed as MabThera (Rituximab,
Rituxan and MabThera are collectively referred to herein as "Rituxan," except
where otherwise indicated). For Rituxan to succeed commercially, the Company,
either alone or through its collaborative relationships, must successfully
manufacture, introduce, market and sell Rituxan. To achieve the successful
commercialization of other product candidates, the Company, alone or through its
collaborative relationships, must successfully develop, obtain FDA or foreign
regulatory approval for, manufacture, introduce, market and sell its potential
products. There can be no assurance that either Rituxan or any other product
candidate will be successfully commercialized. See "Management's Discussion and
Analysis of Financial Condition and Results of Operations."
 
LIMITED MANUFACTURING EXPERIENCE
 
     To be commercially successful, the Company must manufacture its products,
either directly or through third parties, in commercial quantities, in
compliance with regulatory requirements and at an acceptable cost. Although the
Company has produced its products in the laboratory, scaled its production
process to pilot levels and has the ability to manufacture limited commercial
quantities of Rituxan, the Company has only limited experience with regard to
producing such commercial quantities of Rituxan and has not yet received
regulatory approval for commercial production of any other products. In
addition, the Company has limited experience in bulk drug manufacturing in
general and no chemical manufacturing experience, no fill/finish experience, and
no fill/finish capacity. Thus, no assurance can be given as to the ultimate
performance of the Company's manufacturing facility or the Company's ability to
make a successful transition to ongoing commercial production.
 
     Biologics manufacturing as performed by IDEC Pharmaceuticals involves the
growing and harvest of cells and the purification of the target protein by
removal of impurities in controlled environments. This process is extremely
susceptible to product loss due to any microbial or viral contamination of the
process. Since the process is highly defined and controlled, any material
problem due to equipment failure or operator
 
                                        1

<PAGE>   4
 
error could cause the loss of the entire batch being manufactured. Certain
bacterial or viral contaminations could cause the closure of the manufacturing
plant for an extended period of time, until the cause of the contamination is
identified and corrective action is implemented. Certain items of manufacturing
equipment may have long lead times to perform repair and revalidation prior to
use. The Company has attempted to plan for most equipment failure contingencies.
Not all potential problems, however, can be appropriately addressed ahead of
time nor spare parts obtained in a reasonable time frame. Any extended unplanned
plant shutdowns will ultimately create higher manufacturing costs for the
Company and could result in inventory and product shortages.
 
     In March 1995, the Company and Genentech, Inc. ("Genentech") entered into a
collaborative agreement for the clinical development and commercialization of
the Company's anti-CD20 monoclonal antibody, Rituxan, for the treatment of
B-cell non-Hodgkin's lymphomas. In November 1995, the Company, Zenyaku Kogyo,
Ltd. ("Zenyaku") and Genentech entered into a joint development, supply and
license agreement whereby Zenyaku received exclusive rights to develop, market
and sell Rituxan in Japan with the Company receiving royalties on sales of
Rituxan in Japan. The Company's agreement with Genentech calls for IDEC
Pharmaceuticals to commit its full manufacturing capacity to supply Genentech
with bulk Rituxan at the higher of a fixed price per gram or Genentech's cost to
manufacture per gram until the end of 1999. The Company then has the option to
supply Rituxan to Genentech, at the lower of the Company's or Genentech's cost
per gram. The Company currently manufactures Rituxan at a cost in excess of the
Genentech contract's fixed price. Any continuing manufacturing costs above the
contract price per gram or costs attributable to equipment repair or facility
down time could result in an unreimburseable cost, wholly attributable to IDEC
Pharmaceuticals, which would, in turn, result in decreased margins. Furthermore,
the Company is aware that several of its manufacturing software systems are not
yet Year 2000 compliant. See "-- Year 2000 Compliance."
 
DEPENDENCE ON CONTRACT MANUFACTURERS AND SOLE SOURCE SUPPLIER
 
     Although the Company has the ability to manufacture limited commercial bulk
quantities of Rituxan, it is dependent upon Genentech to manufacture additional
worldwide requirements and to complete all the fill/finish production of
Rituxan. Genentech is manufacturing Rituxan in a facility that is still pending
FDA approval for Rituxan manufacture and is currently constructing an additional
manufacturing plant to satisfy long-term demands for Rituxan. Such facility must
be approved by the FDA before it can supply commercial quantities of Rituxan
and, even if approved, there can be no assurance that the Company or Genentech
can manufacture sufficient quantities of Rituxan to meet as yet undetermined
market demands or that Genentech will be able to fill/finish Rituxan on a timely
and cost effective basis to avoid an insufficient supply of Rituxan inventory,
any of which could materially and adversely affect the Company's business,
results of operation and financial condition.
 
     The Company is contractually dependent upon SmithKline Beecham, p.l.c.
("SmithKline Beecham") to fulfill all of the manufacturing requirements for
IDEC-CE9.1 and IDEC-151. SmithKline Beecham has constructed a commercial-scale
manufacturing plant for IDEC-CE9.1 and/or IDEC-151. However, there can be no
assurance that SmithKline Beecham will be able to manufacture sufficient
quantities of IDEC-CE9.1 or IDEC-151, should either or both receive FDA approval
to meet as yet undetermined market demands.
 
     Because the Company's capacity is committed to the manufacture of Rituxan
for two years, the Company does not have the current cell culture capacity to
manufacture commercial qualifying material for the Company's IDEC-Y2B8 or In2B8
products. The Company is currently accepting proposals for a qualified
commercial contractor to meet the long-term manufacturing demands for IDEC-Y2B8
or In2B8. In addition, as the Company does not have expertise or facilities for
small molecule chemical manufacturing, the Company will need to establish a
long-term manufacturing arrangement for the drug 9-aminocamptothecin ("9-AC")
with an appropriate contract manufacturer. The Company's 9-AC clinical materials
requirements will be met over the next two years by Pharmacia & Upjohn S.p.A.
("Pharmacia"), as part of the product in-license agreement. Additionally, as the
Company does not have fill/finish expertise, the Company will be dependent on
outside contractors to meet all of the Company's current and future fill/finish
requirements.
 
     The Company has several vendors for raw materials that are used in the
manufacture of products for commercial or clinical trial use that are the sole
source available. Any disruption in the supply of these
 
                                        2

<PAGE>   5
 
materials would have a material adverse effect on the Company's ability to meet
its manufacturing commitments, and would ultimately have a negative effect on
manufacturing costs, or could delay significantly current clinical studies. Due
to the need for raw materials to meet certain regulatory, pre-qualification and
release specifications prior to their use for manufacturing, the Company is
limited to specific suppliers. The Company has initiated a program for
identifying alternative suppliers for certain raw materials, where possible.
 
LIMITED SALES AND MARKETING EXPERIENCE
 
     The Company has limited experience in commercial sales and marketing. The
Company has adopted a strategy of pursuing collaborative agreements with
strategic partners that provide for co-promotion of certain of the Company's
products. To the extent that the Company elects to participate in co-promotion
efforts in the United States or Canada, and in those instances where the Company
retains exclusive marketing rights in specified territories, the Company will
need to maintain and expand its sales and marketing capability in order to
establish a successful direct sales and marketing capability in the targeted
markets. The Company will also need to build marketing support services
including customer service, order entry, shipping and billing, customer
reimbursement assistance, managed-care sales support, medical information and
sales training. There can be no assurance that the Company will be able to
establish a successful direct sales and marketing capability in any or all
targeted markets or that it will be successful in gaining market acceptance for
its products. To the extent that the Company has entered or in the future enters
into co-promotion or other licensing arrangements, any revenues received by the
Company will be dependent on the efforts of third parties and there can be no
assurance that such efforts will be successful. Failure to establish a sales
capability either in the United States or outside the United States may have a
material adverse effect on the Company's business, results of operations and
financial condition. See "Business -- Sales and Marketing."
 
     During 1998, the Company will depend on the successful marketing and sales
of Rituxan for much of its anticipated revenue. Rituxan is being marketed and
sold in the United States pursuant to a co-promotion agreement with Genentech,
which currently has a sales and marketing staff of approximately 50
professionals that is largely dedicated to the commercialization of Rituxan. In
an effort to establish its own direct sales capability for Rituxan, the Company
has recently created a marketing staff and a sales organization of 32
professionals with experience primarily in the oncology therapeutic category,
who are dedicated exclusively to the commercialization of Rituxan. The Company
relies heavily on Genentech to supply related marketing support services
including customer service, order entry, shipping and billing, customer
reimbursement assistance, managed-care sales support, medical information and
sales training. There can be no assurance that the Company's sales and marketing
staff will successfully transition the Company into long-term profitability.
Furthermore, there can be no assurance that Genentech will successfully perform
its role in the co-promotion relationship.
 
     Outside of the United States and Canada, the Company has adopted a strategy
to pursue collaborative arrangements with established pharmaceutical companies
for marketing, distribution and sale of its products. There can be no assurance
that any of these companies or their sublicensees will successfully market,
distribute or sell the Company's products or that the Company will be able to
establish and maintain successful co-promotion or distribution arrangements.
 
OPERATING RESULTS SUBJECT TO SIGNIFICANT FLUCTUATIONS
 
   
     The Company's quarterly revenues, expenses and operating results are likely
to vary significantly in the future due to a variety of factors such as demand
for the Company's products, the Company's achievement of certain product
development milestone events, hospital and pharmacy buying decisions, physician
acceptance rates, changes in government or private reimbursement policies,
manufacturing constraints, the ability of the Company to obtain approvals of
additional products for commercial sale on a timely basis, changes in the
Company's level of operating expenses, the Company's ability to attract and
retain qualified personnel, changes in the Company's sales incentive plans or
co-promotion agreements, foreign currency exchange rates and overall economic
conditions. Furthermore, because the Company is commercializing Rituxan through
a co-promotion, profit-sharing agreement with Genentech, the Company's ability
to report revenues from the commercialization of Rituxan will be dependent upon
the timeliness of Genentech's reporting of Rituxan sales. There can be no
assurance that Genentech will report on a timely basis. Because the Company's
expense
    
 
                                        3

<PAGE>   6
 
levels are based to a significant extent on the Company's expectations of future
revenues and therefore will vary only slightly in the short term, if revenues
fall below expectations, operating results are likely to be adversely and
disproportionately affected.
 
RELIANCE ON THIRD-PARTY DEVELOPMENT AND MARKETING EFFORTS
 
   
     The Company has adopted a research, development and product
commercialization strategy that is dependent upon various arrangements with
strategic partners and others. The success of the Company's products is
substantially dependent upon the success of these outside parties in performing
their obligations, which include, but are not limited to, providing funding and
performing research and development with respect to the Company's products. The
Company's strategic partners may also develop products that may compete with the
Company. Although IDEC Pharmaceuticals believes that its partners have an
economic incentive to succeed in performing their contractual obligations, the
amount and timing of resources that they devote to these activities is not
within the control of the Company. There can be no assurance that these parties
will perform their obligations as expected or that any revenue will be derived
from such arrangements. The Company has entered into collaborative agreements
with Genentech, Zenyaku, SmithKline Beecham, Mitsubishi Chemical Corporation
("Mitsubishi"), Seikagaku Corporation ("Seikagaku")and Eisai, Co., Ltd.
("Eisai"). These agreements generally may be terminated at any time by the
strategic partner, typically on short notice to the Company. If one or more of
these partners elect to terminate their relationship with the Company, or if the
Company or its partners fail to achieve certain product development milestone
events, it could have a material adverse effect on the Company's ability to fund
the related programs and to develop any products that may have resulted from
such collaborations. There can be no assurance that these collaborations will be
successful. In addition, some of the Company's current partners have certain
rights to control the planning and execution of product development and clinical
programs, and there can be no assurance that such partners' rights to control
aspects of such programs will not impede the Company's ability to conduct such
programs in accordance with the schedules currently contemplated by the Company
for such programs and will not otherwise impact the Company's strategy. See
"Management's Discussion and Analysis of Financial Condition and Results of
Operations" and "Business -- Strategic Alliances."
    
 
LENGTHY REGULATORY PROCESS; NO ASSURANCE OF ADDITIONAL REGULATORY APPROVALS
 
     The testing, manufacturing, labeling, advertising, promotion, export and
marketing, among other things, of the Company's proposed products are subject to
extensive regulation by governmental authorities in the United States and other
countries. In the United States, pharmaceutical products are regulated by the
FDA under the Federal Food, Drug, and Cosmetic Act and other laws, including, in
the case of biologics, the Public Health Service Act. The nature and extent of
regulation by governmental authorities in the United States differs with respect
to different products. At the present time, with the exception of 9-AC, the
Company believes that its products will be regulated by the FDA as biologics.
Biologics require the submission of a Biologics License Application ("BLA") and
approval by the FDA prior to being marketed in the United States. The Company
believes that the FDA will regulate the Company's 9-AC product candidate as a
drug which will require the submission of a New Drug Application ("NDA") for
approval by the FDA prior to being marketed in the United States. The regulatory
approval process for a NDA is similar to the approval process for a BLA.
Manufacturers of biologics or drugs may also be subject to state regulation.
 
     The steps required before a product may be approved for marketing in the
United States generally include (i) preclinical laboratory tests and animal
tests, (ii) the submission to the FDA of an Investigational New Drug application
("IND") for human clinical testing, which must become effective before human
clinical trials may commence, (iii) adequate and well-controlled human clinical
trials to establish the safety and efficacy of the product, (iv) the submission
to the FDA of a BLA or NDA, (v) FDA review of the BLA or NDA and (vi)
satisfactory completion of an FDA inspection of the manufacturing facility or
facilities at which the product is made to assess compliance with current Good
Manufacturing Practices ("cGMP"). The testing and approval process requires
substantial time, effort and financial resources and there can be no assurance
that any approval will be granted on a timely basis, if at all. There can be no
assurance that Phase I, Phase II or Phase III testing will be completed
successfully within any specific time period, if at all, with respect to any of
the Company's product candidates. Furthermore, the FDA may suspend clinical
trials at any
 
                                        4

<PAGE>   7
 
time on various grounds, including a finding that the subjects or patients are
being exposed to an unacceptable health risk.
 
     The results of the preclinical studies and clinical study or studies,
together with detailed information on the manufacture and composition of the
product, are submitted to the FDA in the form of a BLA or NDA requesting
approval to market the product. Before approving a BLA or NDA, the FDA will
inspect the facilities at which the product is manufactured, and will not
approve the product unless cGMP compliance is satisfactory. The FDA may deny a
BLA or NDA if applicable regulatory criteria are not satisfied, require
additional testing or information, and/or require postmarketing testing and
surveillance to monitor the safety or efficacy of a product. There can be no
assurance that FDA approval of any BLA or NDA submitted by the Company will be
granted on a timely basis or at all. Also, if regulatory approval of a product
is granted, such approval may entail limitations on the indicated uses for which
it may be marketed.
 
     Both before and after approval is obtained, violations of regulatory
requirements, including the preclinical and clinical testing process, the BLA or
NDA review process, or thereafter (including after approval) may result in
various adverse consequences, including the FDA's delay in approving or refusal
to approve a product, withdrawal of an approved product from the market, and/or
the imposition of criminal penalties against the manufacturer and/or BLA or NDA
holder. For example, BLA or NDA holders are required to report certain adverse
reactions to the FDA, and to comply with certain requirements concerning
advertising and promotional labeling for their products. Also, quality control
and manufacturing procedures must continue to conform to cGMP regulations after
approval, and the FDA periodically inspects manufacturing facilities to assess
compliance with cGMP. Accordingly, manufacturers must continue to expend time,
monies and effort in the area of production and quality control to maintain cGMP
compliance. In addition, discovery of problems may result in restrictions on a
product, manufacturer or BLA or NDA holder, including withdrawal of the product
from the market. Also, new government requirements may be established that could
delay or prevent regulatory approval of the Company's products under
development.
 
     The Company will also be subject to a variety of foreign regulations
governing clinical trials and sales of its products. Whether or not FDA approval
has been obtained, approval of a product by the comparable regulatory
authorities of foreign countries must be obtained prior to the commencement of
marketing of the product in those countries. The approval process varies from
country to country and the time may be longer or shorter than that required for
FDA approval. At least initially, the Company intends, to the extent possible,
to rely on foreign licensees to obtain regulatory approval for marketing its
products in foreign countries.
 
     In February 1997, the Company and Genentech submitted BLAs to the FDA for
Rituxan as a single agent therapy for the treatment of B-cell non-Hodgkin's
lymphoma, and on November 26, 1997, Rituxan was approved for marketing by the
FDA. Hoffmann-LaRoche submitted an application to the Swiss regulatory agency,
the Office Intercantonal de Controle de Medicaments, for the marketing of
Rituxan in Switzerland. On November 28, 1997, Rituxan was approved for marketing
in Switzerland and was launched in the Swiss market in late 1997 by F.
Hoffmann-LaRoche, Inc. ("Hoffmann-LaRoche"). Hoffmann-LaRoche also submitted a
Marketing Authorization Application ("MAA") with the European Medicines
Evaluation Agency ("EMEA") for marketing Rituxan in the European Union. There
can be no assurance that EMEA approval of the MAA will be granted on a timely
basis, if at all, and delays in receipt or failure to receive regulatory
approval could have a material adverse effect on the Company's business, results
of operations and financial condition.
 
     Under the Orphan Drug Act, the FDA may grant orphan drug designation to
drugs intended to treat a "rare disease or condition," which generally is a
disease or condition that affects fewer than 200,000 individuals in the United
States. Orphan drug designation must be requested before submitting a BLA or
NDA. After the FDA grants orphan drug designation, the generic identity of the
therapeutic agent and its potential orphan use are publicly disclosed by the
FDA. Orphan drug designation does not convey any advantage in, or shorten the
duration of, the regulatory review and approval process. If a product that has
an orphan drug designation subsequently receives FDA approval for the indication
for which it has such designation, the product is entitled to orphan drug
exclusivity, i.e., the FDA may not approve any other
 
                                        5

<PAGE>   8
 
applications to market the same drug for the same indication, except in certain
very limited circumstances, for a period of seven years.
 
     In 1994, the Company obtained orphan drug designation for Rituxan,
IDEC-Y2B8 and IDEC-In2B8 from the FDA to treat certain B-cell non-Hodgkin's
lymphomas (as defined on page 1). In connection with its approval by the FDA,
Rituxan has received orphan drug exclusivity in the United States. However,
there can be no assurance that IDEC-Y2B8 or IDEC-In2B8 will receive orphan drug
exclusivity for the B-cell non-Hodgkin's lymphoma indication, and it is possible
that competitors of the Company could obtain approval, and attendant orphan drug
exclusivity, for IDEC-Y2B8 or IDEC-In2B8 for the B-cell non-Hodgkin's lymphoma
indication, thus precluding the Company from marketing IDEC-Y2B8 or IDEC-In2B8
for that indication in the United States. In addition, even if the Company does
obtain orphan exclusivity for any of its compounds for B-cell non-Hodgkin's
lymphoma, there can be no assurance that competitors will not receive approval
of other, different drugs or biologics for B-cell non-Hodgkin's lymphoma.
Although obtaining FDA approval to market a product with orphan drug exclusivity
can be advantageous, there can be no assurance that the scope of protection or
the level of marketing exclusivity that is currently afforded by orphan drug
designation will remain in effect in the future.
 
UNCERTAINTIES ASSOCIATED WITH CLINICAL TRIALS
 
   
     IDEC Pharmaceuticals has conducted and plans to continue to undertake
extensive and costly clinical testing to assess the safety and efficacy of its
potential products. The rate of completion of the Company's clinical trials is
dependent upon, among other factors, the rate of patient enrollment. Patient
enrollment is a function of many factors, including the nature of the Company's
clinical trial protocols, existence of competing protocols, size of the patient
population, proximity of patients to clinical sites and eligibility criteria for
the study. Delays in patient enrollment will result in increased expenses and
delays, which could have a material adverse effect on the Company's business,
results of operations and financial condition. The Company cannot assure that
patients enrolled in the Company's clinical trials will respond to the Company's
product candidates. Setbacks are to be expected in conducting human clinical
trials. Failure to comply with the FDA regulations applicable to such testing
can result in delay, suspension or cancellation of such testing, and/or refusal
by the FDA to accept the results of such testing. In addition, the FDA may
suspend clinical trials at any time if it concludes that the subjects or
patients participating in such trials are being exposed to unacceptable risks.
Thus, there can be no assurance that Phase I, Phase II or Phase III testing will
be completed successfully within any specific time period, if at all, with
respect to any of the Company's potential products. Further, there can be no
assurance that human clinical testing will show any current or future product
candidate to be safe and effective or that data derived therefrom will be
suitable for submission to the FDA or will support the Company's submission of a
BLA or NDA. See "Business -- Government Regulation."
    
 
PATENTS AND PROPRIETARY RIGHTS
 
     The Company's success will depend, in large part, on its ability to
maintain a proprietary position in its products through patents, trade secrets
and orphan drug designation. IDEC Pharmaceuticals owns by assignment seven
issued and 14 allowed U.S. patents, 16 U.S. patent applications and numerous
corresponding foreign patent applications, and has licenses to patents or patent
applications that are assigned to other entities. No assurance can be given,
however, that the patent applications of the Company or the Company's licensors
will be issued or that any issued patents will provide competitive advantages
for the Company's products or will not be successfully challenged or
circumvented by its competitors. Moreover, there can be no assurance that any
patents issued to the Company or the Company's licensors will not be infringed
by others or will be enforceable against others. In addition, there can be no
assurance that the patents, if issued, would not be held invalid or
unenforceable by a court of competent jurisdiction. Enforcement of the Company's
patents may require substantial financial and human resources. Moreover, the
Company or its licensees may have to participate in interference proceedings if
declared by the U.S. Patent and Trademark Office ("PTO") to determine priority
of inventions, which typically take several years to resolve and could result in
diminished scope of patent protection and substantial cost to the Company.
 
                                        6

<PAGE>   9
 
     A substantial number of patents have already been issued to other
biotechnology and biopharmaceutical companies. Particularly in the monoclonal
antibody field, competitors may have filed applications for or have been issued
patents and may obtain additional patents and proprietary rights relating to
products or processes competitive with or similar to those of the Company. To
date, no consistent policy has emerged regarding the breadth of claims allowed
in biopharmaceutical patents. Moreover, United States and foreign country patent
laws are distinct and the interpretations thereunder unique to each country.
Thus, patentability, validity and infringement issues for the same technology or
invention may be resolved differently in different jurisdictions. There can be
no assurance that patents do not exist in the United States or in foreign
countries or that patents will not be issued that would have an adverse effect
on the Company's ability to market its products. Specifically, the Company is
aware of several patents and patent applications which may affect the Company's
ability to make, use and sell its products. See "Business -- Patents and
Proprietary Rights." Accordingly, the Company expects that commercializing
monoclonal antibody-based products may require licensing and/or cross-licensing
of patents with other companies or entities in this field. There can be no
assurance that the licenses, which might be required for the Company's processes
or products, would be available, if at all, on commercially acceptable terms.
The ability to license any such patents and the likelihood of successfully
contesting infringement, enforceability or validity of such patents are
uncertain and the costs associated therewith may be significant. If the Company
is required to acquire rights to valid and enforceable patents but cannot do so
at a reasonable cost, the Company's ability to manufacture or market its
products would be materially adversely affected.
 
     The owners, or licensees of the owners, of these patents may assert that
one or more of the Company's products infringe one or more claims of such
patents. If legal action is commenced against the Company to enforce any of
these patents and the plaintiff in such action prevails, the Company could be
prevented from making, using, offering to sell, selling or importing the subject
matter claimed in such patents. In such event or under other appropriate
circumstances, the Company may attempt to obtain licenses to such patents.
However, no assurance can be given that any owner would license the patents to
the Company at all or on terms that would permit commercialization of the
Company's products. An inability to commercialize such products could have a
material adverse effect on the Company's business, results of operations and
financial condition.
 
     Furthermore, the patent position worldwide of biotechnology companies in
relation to proprietary products is highly uncertain and involves complex legal
and factual questions. There is a substantial backlog of biotechnology patents
at the PTO. The Company also relies on trade secrets and proprietary know-how
which it seeks to protect, in part, by confidentiality agreements with its
employees, collaborators and consultants. There can be no assurance that these
agreements will not be breached, that the Company will have adequate remedies
for any breach, or that the Company's trade secrets will not otherwise become
known or be independently developed by competitors. See "Business -- Patents and
Proprietary Technology."
 
ADDITIONAL FINANCING REQUIREMENTS AND UNCERTAIN ACCESS TO CAPITAL MARKETS
 
     The Company has expended and will continue to expend substantial funds to
increase sales of Rituxan and to complete the research, development,
manufacturing and marketing of its other products. The Company has obtained and
intends to seek additional funding for these purposes through a combination of
new collaborative arrangements, strategic alliances, and additional equity or
debt financings or from other sources. There can be no assurance that such
future additional funds will be available on acceptable terms, if at all. Even
if available, the cost of funds may result in substantial dilution to current
stockholders. If adequate funds are not available from operations or additional
sources of financing, the Company's business, results of operations and
financial condition could be materially and adversely affected. See
"Management's Discussion and Analysis of Financial Condition and Results of
Operations -- Liquidity and Capital Resources."
 
DEPENDENCE ON KEY PERSONNEL
 
     The Company's success depends in part upon the continued contributions of
its senior management and key scientific and technical personnel. The Company's
success is also dependent upon its ability to attract and retain additional
qualified scientific, technical, manufacturing and managerial personnel and to
develop and
 
                                        7

<PAGE>   10
 
maintain relationships with qualified clinical researchers. Significant
competition exists among pharmaceutical and biotechnology companies for such
personnel, and there can be no assurance that the Company will retain such
personnel or that it will be able to attract, assimilate and retain such
personnel as may be required in the future or to develop and maintain
relationships with such researchers. The Company does not maintain or intend to
purchase "key person" life insurance on any of its personnel. See
"Business -- Employees" and "Directors and Executive Officers of the
Registrant."
 
SUBSTANTIAL COMPETITION
 
     Substantial competition exists in the biotechnology industry from
pharmaceutical and biotechnology companies which may have technical or
competitive advantages. The Company competes with these companies in the
development of technologies and processes and sometimes competes with them in
acquiring technology from academic institutions, government agencies, and other
private and public research organizations. There can be no assurance that the
Company will be able to produce or acquire rights to products that have
commercial potential. Even if the Company achieves product commercialization,
there can be no assurance that one or more of the Company's competitors may not:
(i) achieve product commercialization earlier than the Company, (ii) receive
patent protection that dominates or adversely affects the Company's activities,
(iii) have significantly greater sales and marketing capabilities or (iv)
develop products that are more widely accepted than those developed by the
Company. See "Business -- Competition."
 
VOLATILITY OF STOCK PRICE
 
     The stock market has from time to time experienced significant price and
volume fluctuations that may be unrelated to the operating performance of
particular companies. In addition, the market price of the Company's Common
Stock, like the stock prices of many publicly traded biotechnology companies,
has been highly volatile. During 1997, the Company's stock price fluctuated
between $15 3/4 per share and $46 1/4 per share. Announcements of technological
innovations or new commercial products by the Company or its competitors,
developments or disputes concerning patent or proprietary rights, publicity
regarding actual or potential medical results relating to products or products
under development by the Company or its competitors, regulatory developments in
either the United States or foreign countries, public concern as to the safety
of biotechnology products and economic and other external factors including the
buying and selling of shares by option holders to offset their risk, as well as
period-to-period fluctuations in financial results may have a significant impact
on the market price of the Company's Common Stock. It is likely that in some
future quarter the Company's operating results will be below the expectations of
public market analysts and investors. In such event, the price of the Company's
Common Stock would likely be materially adversely affected. See "Market for
Registrant's Common Equity and Related Stockholder Matters" and "-- Outstanding
Options; Possible Dilution and Hedging."
 
UNCERTAINTIES REGARDING HEALTH CARE REIMBURSEMENT AND REFORM
 
     The future revenues and profitability of biopharmaceutical companies as
well as the availability of capital may be affected by the continuing efforts of
government and third-party payors to contain or reduce costs of health care
through various means. For example, in certain foreign markets pricing or
profitability of prescription pharmaceuticals is subject to government control.
In the United States, there have been, and the Company expects that there will
continue to be, a number of federal and state proposals to implement similar
government controls. While the Company cannot predict whether any such
legislative or regulatory proposals will be adopted, the announcement or
adoption of such proposals could have a material adverse effect on the Company's
business, operating results and financial condition.
 
     The Company's ability to commercialize its products successfully will
depend in part on the extent which appropriate reimbursement levels for the cost
of such products and related treatment are obtained from governmental
authorities, private health insurers and other organizations, such as health
maintenance organizations ("HMOs"). Third-party payors are increasingly
challenging the prices charged for medical products and services. Also, the
trend toward managed health care in the United States and the concurrent growth
of organizations such as HMOs, which could control or significantly influence
the purchase of health
 
                                        8

<PAGE>   11
 
care services and products, as well as legislative proposals to reform health
care or reduce government insurance programs may all result in lower prices for
the Company's products. The cost containment measures that health care payors
and providers are instituting and the effect of any health care reform could
materially adversely affect the Company's business, results of operations and
financial condition. See "Business -- Pharmaceutical Pricing and Reimbursement."
 
     The speed with which Rituxan is adopted into the marketplace will be
dependent on the rate of acceptance of the product into reimbursement programs
operated by governmental authorities, private health insurers and other
organizations, such as HMOs. Any significant delay in the ability of health-care
providers to receive reimbursement for Rituxan will similarly delay the adoption
of Rituxan and could have a material adverse effect on the Company's business,
operating results and financial condition.
 
PRODUCT LIABILITY EXPOSURE
 
     Clinical trials, manufacturing, marketing and sale of any of the products
or products under development owned or licensed by the Company may expose the
Company to product liability claims. The Company currently carries limited
product liability insurance. There can be no assurance that the Company or its
strategic partners will be able to continue to maintain or obtain additional
insurance or, if available, that sufficient coverage can be acquired at a
reasonable cost. An inability to obtain sufficient insurance coverage at an
acceptable cost or otherwise protect against potential product liability claims
could prevent or inhibit the commercialization of pharmaceutical products
developed by the Company or its strategic partners. A product liability claim or
recall could have a material adverse effect on the Company's business, operating
results and financial condition.
 
ENVIRONMENTAL RISKS
 
     The Company's business involves the controlled use of hazardous materials,
chemicals and radioactive compounds. Although the Company believes that its
safety procedures for handling and disposing of such materials comply with the
standards prescribed by state and federal regulations, the risk of accidental
contamination or injury from these materials cannot be completely eliminated. In
the event of such an accident, the Company could be held liable for any damages
that result and any such liability could exceed the resources of the Company. In
addition, disposal of radioactive materials used by the Company in its research
efforts may only be made at approved facilities. Approval of a site in
California has been delayed indefinitely. The Company currently stores such
radioactive materials on site. The Company may incur substantial cost to comply
with environmental regulations. See "Business -- Environmental Regulation."
 
EFFECT OF ANTI-TAKEOVER PROVISIONS
 
   
     The Company has taken a number of actions that could have the effect of
discouraging a takeover attempt that might be beneficial to stockholders who
wish to receive a premium for their shares from a potential bidder. The Company
has adopted a Stockholder Rights Plan that would cause substantial dilution to a
person who attempts to acquire the Company on terms not approved by the
Company's Board of Directors. The Stockholder Rights Plan may therefore have the
effect of delaying or preventing any change in control and deterring any
prospective acquisition of the Company. In addition, the Company's Certificate
of Incorporation grants the Board of Directors the authority to issue up to
8,000,000 shares of Preferred Stock and to determine the price, rights,
preferences and privileges of those shares without any further vote or action by
the Company's stockholders. The rights of the holders of Common Stock will be
subject to, and may be adversely affected by, the rights of the holders of any
shares of Preferred Stock that may be issued in the future. While the Company
has no present intention to issue shares of Preferred Stock, such issuance,
while providing desirable flexibility in connection with possible acquisitions
and other corporate purposes, could have the effect of making it more difficult
or less attractive for a third party to acquire a majority of the outstanding
voting stock of the Company. Such Preferred Stock may also have other rights,
including economic rights senior to the Common Stock, and, as a result, the
issuance thereof could have a material adverse effect on the market value of the
Common Stock. Furthermore, the Company is subject to the anti-takeover
provisions of Section 203 of the Delaware General Corporation Law ("Section
203"), which prohibits the Company from
    
 
                                        9

<PAGE>   12
 
engaging in a "business combination" with an "interested stockholder" for a
period of three years after the date of the transaction in which the person
first becomes an "interested stockholder," unless the business combination is
approved in a prescribed manner. The application of Section 203 also could have
the effect of delaying or preventing a change of control of the Company.
 
OUTSTANDING OPTIONS; POSSIBLE HEDGING AND DILUTION
 
     In September 1997, the Company entered into an agreement with a financial
institution under which the Company sold to the financial institution a call
option, exercisable only at maturity, entitling the financial institution to
purchase from the Company up to 900,000 shares of the Company's Common Stock at
a certain strike price per share. The Company has the right to settle the call
option with cash or stock and, if exercised, the Company expects to settle the
call option by issuing up to 900,000 shares of the Company's Common Stock to the
financial institution. The financial institution has advised the Company that it
has engaged, and may continue to engage, in transactions, including buying and
selling shares of the Company's Common Stock, to offset its risk relating to the
call option, which could affect the market price of the Company's Common Stock.
Furthermore, should the Company settle the call option by issuing stock, new
investors will experience an immediate dilution at the time of issuance. Other
outstanding options and warrants will further dilute the Company's stock.
 
YEAR 2000 COMPLIANCE
 
     Many currently installed computer systems and software products are coded
to accept only two digit entries in the date code field. Beginning in the year
2000, these date code fields will need to accept four digit entries to
distinguish 21st century dates from 20th century dates. As a result, in less
than two years, computer systems and software used by many companies may need to
be upgraded to comply with such "Year 2000" requirements.
 
     Management has initiated an enterprise-wide program to prepare the
Company's computer systems and other electronic applications for the year 2000
(the "Year 2000 Program"). This Year 2000 Program, which is performed by a task
force assembled by the Company, consists of (i) an audit on all electronic and
computer systems in order to identify potential Year 2000 problems within the
Company, (ii) identification of third parties whose Year 2000 non-compliance
would have a material adverse effect on the Company's business, results of
operations or financial condition and requiring such third parties to confirm
that they are developing plans to address their own Year 2000 issues, and (iii)
a remedial phase to correct any discovered problems.
 
   
     The Company's Year 2000 Program has already identified several
manufacturing software systems that are not yet Year 2000 compliant. The Company
expects to complete its audit by the end of February 1998 and intends to
complete its third-party confirmations and begin its remedial phase by the end
of the third quarter in 1998. While the Company has begun evaluating potential
strategies for resolving Year 2000 problems, the dollar amount that the Company
will spend to remediate its Year 2000 issues remains uncertain, and management
has not yet assessed the Year 2000 compliance expenses and related potential
effect on the Company's operations. The Company expects to incur internal
personnel expenses as well as consulting and other expenses related to the
infrastructure and facilities enhancements necessary to prepare the Company's
systems for the year 2000.
    
 
   
     The Company anticipates its Year 2000 Program will be completed before
January 1, 2000. However, there can be no assurance that the Year 2000 Program,
or computer systems and applications of other companies on which the Company's
operations rely, will be timely converted, or that any such failure to convert
by another company would not have a material adverse effect on the Company's
systems. Moreover, a failure to correct any non-compliant manufacturing software
could disable the Company's manufacturing capacity, resulting in inventory and
product shortages and ultimately creating higher manufacturing costs for the
Company. See " -- Limited Manufacturing Experience."
    
 
                                       10

<PAGE>   13
 

                                     PART I
 

ITEM 1. BUSINESS.
 
     IDEC Pharmaceuticals is primarily engaged in the commercialization and
research and development of targeted therapies for the treatment of cancer and
autoimmune and inflammatory diseases. The Company's first commercial product,
Rituxan, and its most advanced product candidate are for treatment of B-cell
non-Hodgkin's lymphomas, which afflict approximately 250,000 patients in the
United States. The Company is also developing products for the treatment of
solid tumors, which afflict approximately 1,100,000 new patients each year in
the Unites States, and rheumatoid arthritis, which afflicts approximately
2,000,000 people in the United States.
 
BACKGROUND
 
     ANTIBODIES AND THE IMMUNE SYSTEM
 
     The immune system is composed of specialized cells, including B cells and T
cells, that function in the recognition, destruction and elimination of disease
causing foreign substances and of virally infected or malignant cells. The role
of these specialized cells is determined by receptors on the cell surface which
govern the interaction of the cell with foreign substances and with the rest of
the immune system. For example, each differentiated B cell of the immune system
has a different antibody anchored to its surface that serves as a receptor to
recognize foreign substances. This antibody then triggers the production of
additional antibodies which as free-floating molecules bind to and eliminate
these foreign substances. Each foreign substance is individually identifiable by
structures on its surface known as antigens, which serve as binding sites for
the specific antibodies. T cells play more diverse roles, including the
identification and destruction of virally infected or malignant cells.
 
     A variety of technologies have been developed to produce antibodies as
therapeutic agents. These include hybridoma technology and molecular biology
techniques such as gene cloning and expression, which can now be applied to the
generation, selection and production of hybrid monoclonal antibody varieties
known as chimeric and humanized antibodies, as well as strictly human
antibodies. Chimeric antibodies are constructed from portions of non-human
species (e.g., mouse) antibodies and human antibodies. In these applications,
the portion of the antibody responsible for antigen binding (the "variable
region") is taken from a non-human antibody and the remainder of the antibody
(the "constant region") is taken from a human antibody. Compared to mouse
("murine") monoclonal antibodies, chimeric antibodies generally exhibit lower
immunogenicity (the tendency to trigger an often adverse immune response such as
a human anti-mouse antibody, or "HAMA" response), are cleared more slowly from
the body, and function more naturally in the human immune system. Humanized
antibodies can be constructed by grafting several small pieces of a murine
antibody's variable region onto a constant region framework provided by a human
antibody. This process, known as "CDR grafting," reduces the amount of foreign
materials in the antibody, rendering it closer to a human antibody. However, the
construction of humanized antibodies by CDR grafting requires complex computer
modeling, and the properties of the resulting antibody are not completely
predictable and may, in fact, still trigger a HAMA response.
 
     B-CELL NON-HODGKIN'S LYMPHOMAS
 
     As with other cell types in the body, B cells and T cells may become
malignant and grow as immune system tumors, such as lymphomas. B-cell
non-Hodgkin's lymphomas are cancers of the immune system which currently afflict
approximately 250,000 patients in the United States. Treatment alternatives for
lymphoma patients include chemotherapy, radiation therapy, and more recently,
the Company's Rituxan that is indicated for use in relapsed or refractory,
low-grade or follicular, CD20 positive, B-cell non-Hodgkin's lymphoma. B-cell
non-Hodgkin's lymphomas are diverse with respect to prognosis and treatment, and
are generally classified into one of three groups (low, intermediate or
high-grade) based on histology and clinical features. These three groups are
further subdivided by the International Working Formulation ("IWF") into
subclasses A through J: low grade (A, B and C); intermediate grade (D, E, F and
G); and high grade (H, I and J). Low grade or follicular B-cell non-Hodgkin's
lymphoma is comprised of IWF subclasses A through D. The Company estimates that
approximately half of the 250,000 patients afflicted with B-cell non-Hodgkin's
 
                                       11

<PAGE>   14
 
lymphoma in the United States have low grade or follicular disease; of these
roughly 18,000 will have been diagnosed during the past 12 months. Patients with
low-grade lymphomas have a fairly long life expectancy from the time of
diagnosis (median survival 6.6 years), despite the fact that low-grade lymphomas
are almost always incurable. Intermediate-grade and high-grade lymphomas are
more rapidly growing forms of these cancers, which in a minority of cases can be
cured with early, aggressive chemotherapy. New diagnoses of non-Hodgkin's
lymphomas have increased approximately 5.9% annually over the past decade, with
55,400 new diagnoses estimated for 1998. The increase is due in part to the
aging of the population and to the increasing prevalence of lymphomas in the
AIDS patient population. In approximately 90% of the cases in the United States,
non-Hodgkin's lymphomas are of B-cell origin, the remainder is of T-cell origin.
 
     Owing to the fluid nature of the immune system, B-cell lymphomas are
usually widely disseminated and characterized by multiple tumors at various
sites throughout the body at first presentation. Treatment courses with
chemotherapy or radiation therapy often result in a limited number of remissions
for patients with B-cell lymphomas. The majority of patients in remission will
relapse and ultimately die either from their cancer or from complications of
standard therapy. Fewer patients achieve additional remissions following relapse
and those remissions are generally of shorter duration as the tumors become
increasingly resistant to subsequent courses of chemotherapy. Therapeutic
product development efforts for these cancers have focused on both improving
treatment results and minimizing the toxicities associated with standard
treatment regimens. Immunotherapies with low toxicity and demonstrated efficacy,
such as Rituxan, might be expected to reduce treatment and hospitalization costs
associated with side effects or opportunistic infections, which can result from
the use of chemotherapy and radiation therapy.
 
     AUTOIMMUNE AND INFLAMMATORY DISEASES
 
   
     Rheumatoid arthritis, systemic lupus erythematosus ("SLE"), psoriasis,
inflammatory bowel disease ("IBD") and multiple sclerosis ("MS") are autoimmune
and inflammatory diseases that require ongoing therapy and afflict more than
6,000,000 patients in the United States. Of these, approximately 2,000,000
people are afflicted with rheumatoid arthritis. Autoimmune disease occurs when
the patient's immune system goes awry, initiating a cascade of events which
results in an attack by the patient's immune system against otherwise healthy
tissue and often includes inflammation of the involved tissue. In rheumatoid
arthritis, the disease attacks the synovial lining of the patient's joints,
usually resulting in the destruction of the joints of the hands, hips and knees.
The patient's condition evolves from constantly painful joints to the disability
of deformed, misaligned joints. Autoimmune diseases such as rheumatoid arthritis
are typically treated with products such as steroids and nonsteroidal,
anti-inflammatory agents and with other therapies, all of which are limited for
several reasons, including their lack of specificity and ineffectiveness when
used chronically. Furthermore, steroids suppress the immune system and make the
patient susceptible to infections while nonsteroidal, anti-inflammatory agents
have been implicated in the formation of gastro-intestinal ulcerations.
    
 
     ANTIBODIES AND THE REGULATION OF IMMUNE SYSTEM CELLS
 
     Monoclonal antibodies may be used to bind to specific subsets of human
immune system cells and may act to deplete or to suppress the activity of the
targeted cells. Indeed, the high specificity of monoclonal antibodies enable
them to discriminately act against different types of B cells or T cells.
Depletion of diseased immune cells or suppression of disease-causing immune
activities may be possible by using antibodies that attach to specific
determinants on the surface of target immune system cells. In particular, the
individual B and T cells of the immune system express a broad variety of surface
determinants (cell surface markers). Such determinants not only differentiate
one cell type from another, but also differentiate individual cells from other
cells with specificity for different antigens. Monoclonal antibodies may also be
used to bind to molecules, such as cytokines, in the plasma which serve as
soluble mediators of immune system cell activity. By neutralizing these
molecules, monoclonal antibodies may be used to alter immune cell activity
and/or migration, for example, in inflammatory conditions.
 
IDEC PHARMACEUTICALS' TECHNOLOGY
 
     IDEC Pharmaceuticals is developing products for the management of immune
system cancers, solid tumors and autoimmune and inflammatory diseases. The
Company's antibody products bind to specific subsets of human immune system
cells, or to soluble mediators of immune cell activity, and act to deplete or to
alter the activity of these cells. The products are administered intravenously
and target cells or soluble
 
                                       12

<PAGE>   15
 
   
mediators located in easily accessible compartments of the body, specifically
the blood, the lymphatic fluid and the synovial fluid. For treatment of
non-Hodgkin's B-cell lymphomas, the Company's products target a cell surface
marker known as CD20 which is present only on B cells but not on B-cell
precursors. These products act to reduce total B-cell levels, including both
malignant and normal B cells. The depletion of normal B cells observed in
clinical experience to date has been only temporary, with regeneration occurring
within months. The Company believes that its recently launched product, Rituxan,
and the successful development of radioimmunotherapeutic agents, such as
IDEC-Y2B8, may provide therapeutic alternatives to complement and, in some
cases, replace chemotherapeutic agents in the treatment of B-cell non-Hodgkin's
lymphomas.
    
 
     Due to their specificity and affinity for cell surface receptors,
monoclonal antibodies are also an attractive means by which to treat autoimmune
diseases. Attachment of monoclonal antibodies to specific cell surface receptors
can be used to suppress aberrant and unwanted immune activity. Historically,
however, the use of monoclonal antibodies as an ongoing therapy has been limited
by the body's rejection of the mouse derived components of the antibodies.
Murine monoclonal antibodies, which are structurally different from human
antibodies, tend to trigger adverse immune reactions when used as therapies.
These reactions include a HAMA response in which the patient's immune system
produces antibodies against the therapeutic antibody, thus limiting its
effectiveness.
 
   
     The Company has developed a proprietary PRIMATIZED(R) antibody technology
designed to avoid HAMA responses and other immunogenicity problems by developing
monoclonal antibodies from primate rather than mouse B cells. These antibodies
are characterized by their strong similarity to human antibodies and by the
absence of mouse components. In March 1996, the Company received a Notice of
Allowance for a U.S. patent application claiming the Company's PRIMATIZED
antibodies. Underlying this proprietary technology is the Company's discovery
that macaque monkeys produce antibodies that are structurally indistinguishable
from human antibodies in their variable (antigen-binding) regions. Further, the
Company found that the macaque monkey can be immunized to make antibodies that
react with human, but not with macaque, antigens. Genetic engineering techniques
are then used to isolate the portions of the macaque antibody gene that encode
the variable region from a macaque B cell. This genetic material is combined
with constant region genetic material from a human B cell and inserted into a
host cell line which then expresses the desired antibody specific to the given
antigen. The result is a part human, part macaque PRIMATIZED antibody which
appears structurally to be so similar to human antibodies that it may be
accepted by the patient's immune system as "self." This development allows the
possibility of therapeutic intervention in chronic diseases or other conditions
that are not amenable to treatment with antibodies containing mouse components.
    
 
     The Company has also discovered a proprietary antigen formulation,
PROVAX(TM), which has shown the ability to induce cellular immunity, manifested
by cytotoxic T lymphocytes, in animals immunized with protein antigens. Cellular
immunity is a counterpart to antibody-based immunity and is responsible for the
direct destruction of virally infected and malignant cells. PROVAX is a
combination of defined chemical entities and may provide a practical means for
the development of effective immunotherapies that act through the induction of
both antibody and cell-mediated immunity. The Company believes such
immunotherapies may be useful for the treatment of certain cancers and viral
diseases. Preliminary studies also indicate that PROVAX can be safely
administered by injection to human subjects. The Company intends to make PROVAX
available through licenses and collaborations to interested partners for
development of immunotherapeutic vaccines.
 
     IDEC Pharmaceuticals has developed methods of engineering mammalian cell
cultures using proprietary gene expression technologies (its "vector
technologies") that rapidly and reproducibly select for stable cells, producing
high levels of desired proteins. These technologies allow the efficient
production of proteins at yields that may be significantly higher, and costs
that may be significantly lower, than current, competing cell culture methods.
IDEC Pharmaceuticals has successfully applied one of these technologies to the
commercial scale production of Rituxan.
 
                                       13

<PAGE>   16
 
PRODUCTS AND PRODUCTS UNDER DEVELOPMENT
 
     Rituxan and the Company's primary products under development address immune
system cancers, such as lymphomas, solid tumors, and autoimmune and inflammatory
diseases, such as rheumatoid arthritis. In addition, the Company has discovered
certain other products through the application of its technology platform. The
products in preclinical and clinical development by the Company include the
following.
 

<TABLE>
<S>                               <C>                        <C>                          <C>
                                  INDICATION                 STATUS(1)                    DEVELOPMENT/MARKETING
                                  -------------------------  -------------------------    -------------------------
IMMUNE SYSTEM CANCER PRODUCTS:
Rituxan.......................    Certain B-cell non-        U.S.: Approved               Genentech (U.S.
                                  Hodgkin's lymphomas                                     co-promotion)
                                                             European Union: MAA          Hoffmann-LaRoche
                                                             pending
                                                             Switzerland: Approved        Hoffmann-LaRoche
                                                             Japan: Phase II              Zenyaku
IDEC-Y2B8.....................    Certain B-cell non-        Phase III                    Hoffmann-LaRoche (option
                                  Hodgkin's lymphomas                                     to commercialize outside
                                  (radioimmunotherapy)                                    the U.S.)
IDEC-In2B8....................    Certain B-cell non-        Phase III                    Hoffmann-LaRoche (option
                                  Hodgkin's lymphomas                                     to commercialize outside
                                  (tumor imaging and                                      the U.S.)
                                  dosimetry)
9-AC..........................    Solid tumors               Phase I/II                   No current partner
AUTOIMMUNE AND INFLAMMATORY PRODUCTS:
PRIMATIZED IDEC-151...........    Rheumatoid arthritis       Phase II portion of Phase I/II SmithKline Beecham
                                                                                          (worldwide)
PRIMATIZED IDEC-CE9.1.........    Rheumatoid arthritis       Phase III - On Clinical      SmithKline Beecham
                                                             Hold                         (worldwide)
PRIMATIZED IDEC-CE9.1.........    Asthma                     Phase I - On Clinical        SmithKline Beecham
                                                             Hold                         (worldwide)
Humanized Anti-gp39               Various autoimmune         Phase I                      Eisai (Europe and Asia)
  (IDEC-131)..................    diseases, initially SLE
PRIMATIZED Anti-gp39..........    Various autoimmune         Lead compound selected       Eisai (Europe and Asia)
                                  diseases
PRIMATIZED Anti-B7............    Various autoimmune         Preclinical development      Mitsubishi (Asia)
                                  diseases, initially
                                  psoriasis
PRIMATIZED Anti-CD23..........    Various allergic           Lead compound selected       Seikagaku (Europe and
                                  conditions, initially                                   Asia)
                                  allergic asthma
Humanized and PRIMATIZED
  Anti-MIF....................    Various Inflammatory       Discovery                    No current partner
                                  conditions
OTHER PRODUCTS:
PROVAX (antigen                   Cancer therapeutic         Phase I(2)                   No current partner
    formulation)..............    vaccines
</TABLE>

 
- ---------------
 
(1) As used in this Prospectus, "Discovery" means that the research phase is
    ongoing and a lead compound has not yet been selected. "Lead compound
    selected" means agents have been identified that meet preselected criteria
    in assays for activity and potency. "Preclinical development" means lead
    compound undergoing testing required prior to submission of IND. "Phase I"
    means initial human studies designed to establish the safety, dose tolerance
    and pharmacokinetics of a compound. "Phase I/II" means initial human studies
    designed to establish the safety, dose tolerance and pharmacokinetics of a
    compound and which may be designed to show preliminary activity of a
    compound in patients with the targeted disease. "Phase II" means human
    studies designed to establish safety, optimal dosage and preliminary
    activity of a compound. "Phase III" means human studies designed to lead to
    accumulation of data sufficient to support a BLA, including data relating to
    efficacy. For a further description of "On Clinical Hold," see "-- Products
    and Products Under Development -- Autoimmune and Inflammatory
    Products -- PRIMATIZED IDEC-151 and IDEC-CE9.1.
 
(2) Although Phase I trials have been completed, the Company does not intend to
    pursue further development unless and until it enters into a partnering
    arrangement for such development.
 
                                       14

<PAGE>   17
 
     IMMUNE SYSTEM CANCER PRODUCTS
 
     IDEC Pharmaceuticals' objective with respect to treating non-Hodgkin's
B-cell lymphomas is to use its pan-B antibodies to target, bind to and
selectively eliminate both the patient's normal and malignant B cells.
 
     Rituxan. Rituxan is a genetically engineered, chimeric murine/human
monoclonal antibody designed to harness the patient's own immune mechanisms to
destroy tumor cells. Rituxan was approved by the FDA for treatment of certain
B-cell non-Hodgkin's lymphomas. Rituxan has also been approved in Switzerland
and other European approvals are pending. Laboratory studies performed by the
Company have shown that the antibody attaches to the CD20 antigen on B cells and
activates a group of proteins known as "complement," leading to normal and
malignant B-cell destruction. Additionally, the antibody, when bound to the CD20
antigen, recruits macrophages and natural killer cells to attack the B cell.
Through these and other mechanisms, the antibody utilizes the body's immune
defenses to lyse (rupture) and deplete B cells. B cells have the capacity to
regenerate from early precursor cells that do not express the CD20 determinant.
The depletion of normal B cells observed in clinical experience to date has been
only temporary, with normal B-cell regeneration typically occurring within six
to nine months. The capacity of a tumor to regrow after treatment with Rituxan
will depend on the number of malignant B cells, or malignant B-cell precursors
(if the malignancy first appeared within a precursor cell), remaining after
treatment.
 
   
     Rituxan is the first monoclonal antibody approved by the FDA for a cancer
therapy indication. Rituxan is unique in the treatment of non-Hodgkin's lymphoma
due to its specificity for the antigen CD20, which is expressed only on normal
and malignant B cells, but not on other tissues of the body, and mechanism of
action as compared to conventional lymphoma therapies. These properties of
Rituxan contribute to the agent's favorable side effect profile as compared to
chemotherapy and allows its use in clinical settings where chemotherapy is
either poorly tolerated or ineffective in inducing disease remissions. Rituxan
is easily administered in the outpatient setting by personnel trained in the use
of chemotherapies. A full course of Rituxan therapy consists of four intravenous
infusions given on days 1, 8, 15 and 22, whereas chemotherapy is given typically
in repeating cycles for up to four to eight months.
    
 
   
     Rituxan is indicated for single agent use in relapsed or refractory, low
grade or follicular, CD20 positive, B-cell non-Hodgkin's lymphomas, which
comprise about half of the prevalence of the disease in the United States.
Ongoing or completed Phase II studies suggest that Rituxan may also be useful in
combination with chemotherapy in low grade or follicular lymphomas, and as a
single agent, or in combination with various chemotherapies, in the treatment of
other forms of non-Hodgkin's lymphoma. In Phase III clinical trials, Rituxan
given as a single agent to patients with relapsed or refractory, low grade or
follicular, CD20 positive, B-cell non-Hodgkin's lymphoma, demonstrated tumor
shrinkage in 87% of patients. Fifty percent of evaluable patients (76 of 151
patients) achieved partial or complete responses to therapy, i.e., achieved
tumor shrinkage of greater than 50%. The median time to progression (time to
tumor regrowth following treatment) in these 76 responders had not been reached
at 12.5 months following initiation of therapy, despite the short duration (22
days) of the full course of therapy. Rituxan has been well tolerated in clinical
studies with side effects being primarily mild to moderate flu-like symptoms
that generally are limited to the period of infusion. As compared to
chemotherapy, Rituxan does not harm the bone marrow and therefore does not cause
the myelosuppression that is a source of much of chemotherapy-associated
morbidity and mortality. Also, Rituxan has been shown to induce meaningful
remissions of disease in poor prognosis patients such as the elderly, patients
failing autologous bone marrow transplants and/or anthracycline containing
therapies, and patients who have become refractory to chemotherapy.
    
 
   
     In 1996, the Company and Genentech completed a Phase III trial of Rituxan
at over 30 clinical sites including leading cancer centers in the United States
and Canada. In this Phase III open label, single arm testing of Rituxan as a
single agent therapeutic, each of the patients participating in the study
received four infusions of the antibody on an outpatient basis during a 22-day
period. Of the 166 patients entered into the study, 161 completed all four
courses of therapy. Of the 166 patients entered into the study, 151 patients
were evaluable for response rate analysis. The 15 patients not considered
evaluable, due to lack of therapy completion or protocol violations, are
included in the overall response rate as non-responders. Of 166 patients
entered, 80 responded (showed at least 50% reduction in tumor size) to treatment
with Rituxan, for an overall
    
 
                                       15

<PAGE>   18
 
response rate of 48%. Ten of these responses were complete responses (6%) and 70
were partial responses (42%). As of the most recent analysis, of the responding
patients, 47% were still in remission at over 12.5 months' median follow-up,
with the longest ongoing duration of response at 22.8 months.
 
     The following table shows the percentage change in tumor size in all 166
patients entered into the Phase III trial of Rituxan in B-cell non-Hodgkin's
lymphoma. Though all patients had progressive disease at the initiation of
treatment, 87% showed evidence of reduction in tumor bulk. Among the responders
(tumor shrinkage of at least 50%), the median tumor shrinkage was 90%.
 
     MAXIMUM PERCENTAGE CHANGE IN TUMOR SIZE AMONG ALL TREATED PATIENTS(1)
 
               [CHART DETAILING PERCENTAGE CHANGE IN TUMOR SIZE]
 
       (1) Tumor shrinkage measured radiographically for the 166 patients
           by sum of products of lesion perpendicular diameters. Data
           represents the greatest shrinkage achieved by each patient
           during the observation period. Subsequent tumor growth may
           have occurred and data for three patients are unavailable.
 
       (2) Includes two patients with increase in lesion size greater
       than 100%.
 
     Retrospective analysis of patient subgroups in the Phase III Rituxan trial
showed responses in patients with poor prognostic features such as age greater
than 60, extranodal disease, prior relapse from autologous bone marrow
transplant, or relapse or failure of anthracycline containing regimens.
 
     The most common adverse events associated with Rituxan, based on the
Company's clinical trial experience, were infusion-related, consisting mainly of
mild to moderate flu-like symptoms (e.g., fever, chills, rigors) that occurred
in the majority of patients during the first infusion. Other events which
occurred with less frequency included nausea, rashes, fatigue and headaches.
More serious events included hypotension, wheezing, sensation of tongue or
throat swelling and recurrence of cardiac events in patients with a history of
angina or arrhythmia. These symptoms were usually limited in duration to the
period of infusion and
 
                                       16

<PAGE>   19
 
decreased with subsequent infusions. These adverse events are generally more
mild and of a shorter duration than the adverse events associated with
chemotherapy.
 
     In addition to these findings, the Company observed the disappearance from
the patients' bone marrow of a chromosomal translocation marker (bcl-2)
associated with malignant cells, which was present prior to treatment. The tumor
marker gene reverted to negative in the peripheral blood of over 70% of the
patients who were positive at baseline, and in the bone marrow of over 50% of
patients who were positive at baseline. Researchers have previously reported
clearance of this marker from bone marrow with marrow transplantation regimens
incorporating ex-vivo marrow purging and only rarely with chemotherapy regimens.
However, the clinical significance of bcl-2 conversion has not yet been
determined.
 
   
     The completion of the Phase III clinical trial supported the submission to
the FDA in February 1997, by the Company and Genentech, of BLAs for Rituxan as a
single agent therapy for the treatment of relapsed or refractory, low grade or
follicular, CD20 positive, B-cell non-Hodgkin's lymphoma. Hoffmann-LaRoche also
submitted a MAA with the EMEA for marketing Rituxan (under the trade name
MabThera) in Europe. On November 26, 1997, IDEC Pharmaceuticals received
approval from the FDA to begin marketing Rituxan in the United States. On
November 28, 1997, Hoffmann-LaRoche received approval to begin marketing
MabThera in Switzerland. Approval to begin marketing in the 15 European Union
countries is not anticipated until mid-1998, at the earliest.
    
 
     In an effort to identify expanded applications for Rituxan, the Company, in
conjunction with Genentech, has authorized over 35 Rituxan post-marketing trials
to date. Several of these trials will explore the use of Rituxan in a variety of
investigational B-cell non-Hodgkins lymphoma clinical settings including: (i)
combination therapy with widely used chemotherapy regimens for both low grade
and intermediate/high grade disease; (ii) single agent therapy in newly
diagnosed, previously untreated low grade disease; (iii) integration into
autologous bone marrow transplant regimens both as an in-vivo purging agent
prior to bone marrow harvest and post-transplant as consolidation therapy; and
(iv) treatment of AIDS-related lymphoma. Additionally, clinical trials will be
initiated in other B-cell malignancies and pre-malignant conditions such as
chronic lymphocyte leukemia ("CLL"), multiple myeloma and lymphoproliferative
disorders associated with solid organ transplant therapies.
 
   
     Also, the Company and Genentech have committed to providing drug to a small
group of trials to be undertaken by National Cancer Institute ("NCI") funded
cooperative study groups. At least two of these trials will be large Phase III
studies designed to explore the utility of Rituxan in combination with standard
chemotherapy regimens. No assurance can be given that such trials will be
successful or that any of them will lead to a broadening of the usage of
Rituxan.
    
 
     IDEC-Y2B8 and IDEC-In2B8. Due to the sensitivity of B-cell tumors to
radiation, radiation therapy has historically played, and continues to play, an
important role in the management of B-cell lymphomas. Radiation therapy
currently consists of external beam radiation focused on certain areas of the
body with tumor burden. IDEC Pharmaceuticals is developing two antibody products
which are intended to deliver targeted immunotherapy by means of injectable
radiation to target sites expressing the CD20 determinant, such as lymphatic
B-cell tumors, targeted for later stage patients requiring more aggressive
treatment. In clinical testing, IDEC-In2B8 is first used to image the patient's
tumor and to ensure that normal organs are not exposed to undue radiation from
the subsequently administered therapeutic product. The low-energy gamma particle
emitted by IDEC-In2B8 is detectable outside the body, thereby allowing the
physician to determine the localization of the antibody in the tumor. The
companion therapeutic product, IDEC-Y2B8, provides targeted radiation therapy by
emitting a high-energy beta particle that is absorbed by surrounding tissue,
leading to tumor destruction. The Company's objective with these products is to
provide safer, more effective radiation therapy than is possible with external
beam radiation and to provide this radiation therapy in an outpatient setting.
 
     IDEC-Y2B8 is an anti-CD20 murine antibody that is securely bound to the
isotope yttrium-90. This radioisotope is well suited for therapeutic purposes
because of its energy, radius of activity and half-life. It emits only beta
radiation. Other radioisotopes, such as iodine-131, emit both beta and gamma
radiation and at certain therapeutic doses require that the patient be
hospitalized and isolated in a lead-shielded room for
 
                                       17

<PAGE>   20
 
several days. In contrast, the beta particle emitted by yttrium-90 is absorbed
by tissue immediately adjacent to the antibody. The Company believes that this
short penetrating radiation will permit the use of the product in outpatient
therapy, and has conducted its clinical trials in the outpatient setting.
 
     The Company completed a dose-escalating Phase I clinical trial with
IDEC-Y2B8 in early 1995. Single doses of IDEC-Y2B8 showed clinical activity
comparable to that of intensive, multiple dose, salvage chemotherapy, with
response durations exceeding those of the patients' most recent chemotherapy. In
August 1996, the Company initiated a clinical trial that incorporates both
IDEC-Y2B8 and Rituxan, and preliminary results of this trial were reported at
the December 1997 meeting of the American Society of Hematology ("ASH"). In this
open label, Phase I/II clinical trial, patients with advanced, relapsed B-cell
non-Hodgkin's lymphoma received pretreatment with Rituxan to maximize tumor
localization and efficacy of subsequently administered IDEC-Y2B8. Patients
received 250mg/m(2) of Rituxan plus an imaging dose of IDEC-In2B8 on day one.
During the following week, patient tumors were imaged using the low-energy gamma
radiation emitted by the indium isotope. On day eight, patients received a
second infusion of Rituxan at 250mg/m(2) followed by a therapeutic dose of
IDEC-Y2B8 at 0.2, 0.3 or 0.4 mCi/kg of body weight. Across all dose groups, an
82% response rate was seen in the subpopulation of B-cell non-Hodgkin's lymphoma
(with a total of 31 patients having been evaluated). At the dose group of 0.4
mCi/kg, a 100% overall response rate was seen (seven of seven patients) in this
patient population.
 
     The Company has initiated a Phase III trial of IDEC-Y2B8 for the proposed
treatment of B-cell non-Hodgkin's lymphoma. Accrual for this trial should be
completed in approximately one year. For this trial, 0.4 mCi/kg has been
selected as the standard dose, with patients having low platelet counts being
eligible for treatment at the lower dose of 0.3 mCi/kg.
 
     The Company expects that Rituxan and IDEC-Y2B8 will provide complementary
products for the management of non-Hodgkin's lymphomas. Because most lymphomas
are treated today in community-based group practices, Rituxan fits nicely into
the community practice, as no special equipment or extensive training is
required for its administration or for management of treatment related side
effects. Rituxan has shown activity even in patients refractory to chemotherapy
and is indicated for this use, so that it may provide a viable option for the
community-based oncologist prior to referral of the patient to the major medical
center for treatment with more aggressive therapies, potentially including
IDEC-Y2B8. By contrast, all radioimmunotherapies will be administered by the
nuclear medicine specialist or radiation oncologist at the major medical center
that is equipped for the handling, administration and disposal of radioisotopes.
Also, the nuclear medicine department, but not the community-based practice, has
the specialized equipment and governmental licenses that are required for use of
radioisotopes. Thus the Company believes that referral patterns will develop for
treatment of lymphoma patients with radioimmunotherapies at major medical
centers after the community-based oncologist has exhausted all other options,
such as Rituxan or chemotherapy, for the management of his or her patients. This
trend will be further reinforced by the observation made by the Company, and by
others working in the field, of the substantial clinical activity of
radioimmunotherapies in patients with late-stage disease that has become
refractory to chemotherapies. Thus, IDEC Pharmaceuticals is committed to the
development and commercialization of Rituxan and the investigational agent
IDEC-Y2B8 as complementary products which might be used throughout the course of
a patient's disease providing alternatives, for both the patient and the
healthcare professional, to conventional chemotherapies.
 
   
     9-Aminocamptothecin. In July 1997, IDEC Pharmaceuticals completed its
acquisition of worldwide rights to 9-AC from Pharmacia. This drug was acquired
as part of a consent decree issued by the Federal Trade Commission ("FTC")
regarding the merger of Pharmacia AB with The Upjohn Company. IDEC
Pharmaceuticals now holds exclusive rights to all licenses and technology
related to 9-AC and is proceeding with clinical development of the compound. In
preclinical and Phase I/II clinical studies conducted by Pharmacia and the NCI,
9-AC has shown broad-spectrum activity against a variety of solid tumors. A
semi-synthetic analogue of the plant-derived molecule camptothecin, 9-AC belongs
to a class of drugs known as camptothecins that interferes with DNA replication
by inhibiting a critical nuclear enzyme, topoisomerase I. During 1996, two
compounds from the camptothecin class were approved for marketing by the FDA:
Hycamptin(R) (SmithKline Beecham) for the treatment of ovarian cancer and
Camptosar(R) (Pharmacia) for the treatment of colorectal cancer. In October
1997, the Company announced that it had begun treating
    
 
                                       18

<PAGE>   21
 
   
patients as part of a Phase I/II clinical trial of 9-AC. The trial is aimed at
verifying the maximum tolerated dose of 9-AC, determined by other investigators
in earlier trials, and at seeking an initial indication to pursue for marketing
approval. The investigational study population includes patients with any one of
eight solid tumor types: non-small cell lung, colorectal, pancreatic, gastric,
bladder, prostate, head and neck, or kidney. The initial protocol of the Phase
I/II study, being managed at the University of Alabama, is an escalating dose
safety study of 9-AC in nine patients. Once the maximum tolerated dose is
confirmed, the Company expects that patients, up to a total of 14 individuals in
each of the targeted tumor types, will be enrolled in Phase IIA of the study.
The Company intends to involve additional centers in the Phase II portion of the
trial. If the investigators see at least one response in any tumor type,
additional patients with that cancer will be studied in Phase IIB of the trial
to determine an estimate of the response rate for that disease. Once the
investigators identify a meaningful response rate for one or more tumor types,
the Company intends to choose one of those indications to take into a
registration or pivotal study.
    
 
     AUTOIMMUNE AND INFLAMMATORY PRODUCTS
 
   
     IDEC Pharmaceuticals is developing a new class of antibodies, termed
PRIMATIZED antibodies, that are of part human, part macaque monkey, origin.
These antibodies are structurally similar to, and potentially indistinguishable
by a patient's immune system from, human antibodies. PRIMATIZED antibodies may
provide therapeutic intervention for diseases or conditions not amenable to
chronic treatment with mouse-derived antibodies. The Company's objective with
its PRIMATIZED antibodies is to provide therapies that can be used to control
autoimmune diseases characterized by overactive immune functions. The Company
has entered into research and development collaborations with SmithKline
Beecham, Mitsubishi, Seikagaku and Eisai, all of which utilize the Company's
PRIMATIZED technology and which target distinct, cell surface determinants or
soluble mediators. See "-- Strategic Alliances."
    
 
     PRIMATIZED IDEC-151 and IDEC-CE9.1. In June 1997, the Company and
SmithKline Beecham announced that they had suspended further enrollment and
treatment in the Phase III and supportive clinical trials of IDEC-CE9.1
(designated SB-210396 by SmithKline Beecham for its clinical development) for
the treatment of rheumatoid arthritis. This decision was based on observations
of lowered CD4 cell counts in a higher number of treated patients in the Phase
III study compared to the rate observed in the earlier Phase II trial. While
there have been no reports of side effects related to lower CD4 counts in the
Phase III trial, the companies decided to place a hold on clinical trials with
IDEC-CE9.1 pending a thorough review and analysis of the data. The Company
expects to receive the analysis of this information in February 1998.
 
     A blinded assessment of CD4 cell counts in the Phase III trial of
IDEC-CE9.1 showed that 35 out of 103 patients completing the first month of
treatment had reduced CD4 cell counts, compared to 10 of 136 measured at the
same point in the Phase II trial. Five of these ten patients in Phase II had a
reduction of CD4 counts for three months or longer. The duration of CD4 count
reduction in the Phase III trial will be assessed as part of the ongoing
follow-up. No efficacy assessment has been made to date in the Phase III trial,
but an evaluation will be made for patients who have completed the initial part
of the trial. The earlier Phase II study demonstrated significant clinical
improvement in the signs and symptoms of rheumatoid arthritis with IDEC-CE9.1
treatment. For example, according the American College of Rheumatology ACR-20
composite endpoint, 69%, 51% and 42% response rates were seen in the 140mg, 80mg
and 40mg dose groups, respectively, versus 19% in the placebo group in this
double-blinded, Phase II study.
 
     The reason for the observed discrepancy in frequency of CD4 depletion
between the Phase III trial and the earlier Phase II experience is uncertain.
Potential sources of this variation, including dose and schedule changes,
manufacturing changes and patient variables, will be investigated as part of a
comprehensive review of preclinical and clinical data. This assessment will
guide decisions regarding the further development of IDEC-CE9.1.
 
     In addition to the IDEC-CE9.1 antibody, a second generation anti-CD4
antibody, IDEC-151 (designated SB-217969 by SmithKline Beecham for its clinical
development), is currently in a Phase I/II trial for rheumatoid arthritis. This
antibody is similar in its CD4 binding properties to IDEC-CE9.1, but is
engineered with a human gamma 4 constant region with reduced cell depletion
potential. On December 2, 1997, the
 
                                       19

<PAGE>   22
 
Company and SmithKline Beecham announced results of the Phase I portion of this
trial for the treatment of rheumatoid arthritis. The findings in this single
dose, dose-escalating, placebo-controlled, double-blinded portion of the study
in 32 patients with moderate to severe rheumatoid arthritis, showed no depletion
in CD4 cells, no infusion-related adverse events, and longer coating action when
IDEC-151 was administered at high doses compared to the first generation
PRIMATIZED antibody, IDEC-CE9.1. Longer cell-coating action may be important for
enhanced clinical activity and may enable less frequent dosing as compared to
IDEC-CE9.1. During the first half of 1998, the Company and SmithKline Beecham
expect to determine the development courses to take with the two antibodies that
they have in joint development. One possible outcome is the decision to abandon
IDEC-CE9.1 in preference for IDEC-151, pending a successful outcome with the
latter antibody in the ongoing multi-dose portion of the Phase I/II trial.
 
     Humanized Anti-gp39 (IDEC-131) and PRIMATIZED Anti-gp39. In December 1995,
the Company entered into a research and development collaborative agreement with
Eisai. The collaboration focuses on developing humanized and PRIMATIZED
antibodies against the gp39 antigen. This antigen, also referred to as the CD40
ligand, is an essential immune system trigger for B-cell activation and antibody
production. Potential target indications include transplantation and
antibody-mediated autoimmune diseases such as idiopathic thrombocytopenic
purpura ("ITP") and SLE. The development of the Company's humanized anti-gp39
monoclonal antibody ("IDEC-131") is based on technology that the Company
licensed from Dartmouth College, where researchers have shown that the binding
of gp39 to its CD40 receptor on B cells is essential for proper immune system
function. These researchers generated anti-gp39 antibodies that blocked this
T-cell and B-cell interaction and halted disease progression in a variety of
animal models of disease characterized by abnormal or unwanted immune response.
Moreover, when researchers ended the animals' anti-gp39 treatments, the animals'
antibody-producing capacity returned to normal levels, but their disease
remained suppressed. Treatment with the anti-gp39 antibodies appeared to have
reset the animals' immune systems and restored a normal immune response. Under
the collaborative agreement, the Company and Eisai have agreed to develop a
humanized anti-gp39 antibody and launch additional efforts to develop a second
generation, PRIMATIZED anti-gp39 antibody. This effort has resulted in the
identification of the humanized anti-gp39 antibody lead candidate, IDEC-131,
which underwent preclinical testing, process development and manufacturing of
clinical trial material in early 1997. The Company filed an IND for IDEC-131 in
November 1997 and began a Phase I clinical study in SLE in February 1998.
 
     PRIMATIZED Anti-B7. In November 1993, the Company entered into a research
and development collaboration with Mitsubishi that focuses on the development of
PRIMATIZED antibodies directed at a B7 determinant. This B7 determinant appears
on the surface of antigen-presenting cells and is involved in the interaction of
these cells with T cells in triggering a cascade of immune system responses.
Antibodies directed at B7 determinants may block this cascade and, therefore,
may be useful in preventing unwanted immune responses in certain inflammatory
and chronic autoimmune conditions such as psoriasis, arthritis and MS.
Mitsubishi has actively shared in the development process, generating animal
models and participating in research with the Company. This effort has resulted
in the identification of a PRIMATIZED antibody lead candidate which is
undergoing preclinical testing, process development and manufacturing of
clinical material.
 
     PRIMATIZED Anti-CD23. In December 1994, the Company entered into a
collaboration with Seikagaku aimed at the development of PRIMATIZED anti-CD23
antibodies for the potential treatment of allergic rhinitis, asthma and other
allergic conditions. Antibodies against the CD23 receptor on certain white blood
cells inhibit the production of immune system molecules called immunoglobulin
class E, or IgE, which are known to trigger allergic conditions. At the same
time, anti-CD23 antibodies do not affect the production of the immunoglobulins
(the patient's own antibodies) responsible for granting protective immunity to
infectious agents. Thus, PRIMATIZED anti-CD23 antibodies may provide a unique
new approach to treating chronic illnesses such as allergic rhinitis and asthma.
This effort has resulted in the identification of a PRIMATIZED antibody lead
candidate which is expected to undergo preclinical testing, process development
and manufacturing of clinical material during 1998.
 
     Humanized and PRIMATIZED Anti-MIF. MIF (macrophage migration inhibitory
factor) is the body's natural counter-regulatory cytokine which serves to
override the anti-inflammatory activities of natural and administered steroids.
Inhibition of MIF may represent a novel approach to the management of a variety
of
 
                                       20

<PAGE>   23
 
   
acute and chronic inflammatory diseases, including steroid-resistant rheumatoid
arthritis and asthma. In September 1997, IDEC Pharmaceuticals licensed from
Cytokine Networks, Inc. ("CNI"), a privately-held biopharmaceutical company,
development rights to CNI's anti-MIF antibody technology. Under the terms of the
licensing and development agreement, the Company became the exclusive licensee
of CNI's rights to the anti-MIF antibody technology for therapeutic and
diagnostic applications. In return for these rights, the Company made a $3.0
million preferred equity investment in CNI, which will also receive product
development milestone payments and royalties on the sales by the Company of
approved products resulting from the collaboration.
    
 
STRATEGIC ALLIANCES
 
   
     The Company has entered into one or more strategic partnering arrangements
for each of its principal product development programs. Through these strategic
partners, the Company is funding a significant portion of its product
development costs and is capitalizing on the production, development,
regulatory, marketing and sales capabilities of its partners. Unless otherwise
indicated, the amounts shown below as potential payments include license fees,
product development milestone payments, research and development fees and, with
respect to Genentech, SmithKline Beecham and Zenyaku, equity investments, but do
not include potential royalties. The Company's entitlement to such payments
depends on achieving milestones related to development, clinical trials results
and regulatory approvals and other factors. These arrangements include:
    
 
   
     Genentech, Inc. In March 1995, the Company and Genentech entered into a
collaborative agreement for the clinical development and commercialization of
the Company's anti-CD20 monoclonal antibody, Rituxan, for the treatment of
B-cell non-Hodgkin's lymphomas. In November 1995, the Company, Zenyaku and
Genentech entered into a joint development, supply and license agreement
pursuant to which Zenyaku received exclusive rights to develop, market and sell
Rituxan in Japan and the Company will receive royalties on sales of Rituxan in
Japan. Concurrent with the collaborative agreement, the Company and Genentech
also entered into an expression technology license agreement for a proprietary
gene expression technology developed by the Company and a preferred stock
purchase agreement providing for certain equity investments in the Company by
Genentech. Under the terms of the Genentech agreements, the Company may receive
payments totaling $58.5 million, subject to the attainment of certain product
development milestone events, of which $48.5 million has been recognized through
December 31, 1997. In addition, the Company and Genentech are co-promoting
Rituxan in the United States. Genentech retained commercialization rights
throughout the rest of the world, except in Japan. Genentech has granted
Hoffmann-LaRoche marketing rights outside of the United States, and
Hoffmann-LaRoche has elected to market Rituximab under the trade name Mabthera.
The Company and Hoffmann-LaRoche are currently discussing an arrangement for
commercialization of Rituxan in Canada, but no assurance can be given that an
arrangement will be found which will be satisfactory to the Company,
Hoffmann-LaRoche and Genentech, which previously held co-promotion rights to
Canada along with IDEC Pharmaceuticals. The Company will receive royalties on
sales outside the United States and Canada. The collaborative agreement between
the Company and Genentech provides two independent mechanisms by which either
party may purchase or sell its rights in the co-promotion territory from/to the
other party. Upon the occurrence of certain events that constitute a change of
control of the Company, Genentech may elect to present an offer to the Company
to purchase the Company's co-promotion rights. The Company must then accept
Genentech's offer or purchase Genentech's co-promotion rights for an amount
scaled (using the profit sharing ratio between the parties) to Genentech's
offer. Under a second mechanism, after a specified period of commercial sales
and (i) upon a certain number of years of declining co-promotion profits or (ii)
if Genentech files for U.S. regulatory approval on a competitive product during
a limited period of time, either party may offer to purchase the other party's
co-promotion rights. The offeree may either accept the offer price or purchase
the offeror's co-promotion rights at the offer price scaled to the offeror's
share of co-promotion profits.
    
 
     SmithKline Beecham, p.1.c. In October 1992, the Company and SmithKline
Beecham entered into an exclusive worldwide collaborative research and license
agreement limited to the development and commercialization of therapeutic
products based on the Company's PRIMATIZED anti-CD4 antibodies. Under the terms
of this agreement, the Company may receive payments in excess of $60.0 million,
subject to the
 
                                       21

<PAGE>   24
 
   
attainment of certain product development milestone events, of which $32.6
million has been recognized through December 31, 1997. The Company will receive
funding for anti-CD4 related research and development programs, as well as
royalties and a share of co-promotion profits in the United States and Canada on
sales of products which may be commercialized as a result of the collaboration.
At any time, SmithKline Beecham may terminate this agreement by giving the
Company thirty days' written notice based on a reasonable determination that the
products do not justify continued development or marketing. In connection with
the collaboration, SmithKline Beecham purchased shares of the Company's Common
Stock and warrants exercisable into Common Stock.
    
 
   
     Mitsubishi Chemical Corporation. In November 1993, the Company entered into
a three-year collaborative agreement and an ongoing license agreement with
Mitsubishi for the development of a PRIMATIZED anti-B7 antibody. Under the terms
of the agreement, the Company may receive payments totaling $12.2 million to
fund research of the PRIMATIZED anti-B7 antibody, subject to the attainment of
certain product development milestone events, of which $7.2 million has been
recognized through December 31, 1997. Under the agreement, the Company has
granted Mitsubishi an exclusive license in Asia to make, use and sell PRIMATIZED
anti-B7 antibody products. The Company will receive royalties on sales by
Mitsubishi of the developed products. At any time, Mitsubishi may terminate this
agreement by giving the Company thirty days' written notice based on a
reasonable determination that the products do not justify continued development
or marketing or based on failure to reach milestones.
    
 
   
     Seikagaku Corporation. In December 1994, the Company and Seikagaku entered
into a collaborative development agreement and a license agreement aimed at the
development and commercialization of therapeutic products based on the Company's
PRIMATIZED anti-CD23 antibodies. Under the terms of these agreements, Seikagaku
may provide up to $26.0 million in milestone payments and support for research
and development, subject to the attainment of certain product development
milestone events, of which $14.5 million has been recognized through December
31, 1997. Under the agreement, Seikagaku has received exclusive rights in Europe
and Asia to all products emerging from the collaboration. The Company will
receive royalties on eventual product sales by Seikagaku. At any time, Seikagaku
may terminate this agreement by giving the Company sixty days' written notice
based on a reasonable determination that the products do not justify continued
development or marketing.
    
 
   
     Eisai Co., Ltd. In December 1995, the Company and Eisai entered into a
collaborative development agreement and a license agreement aimed at the
development and commercialization of humanized and PRIMATIZED anti-gp39
antibodies. Under the terms of these agreements, Eisai may provide up to $37.5
million in milestone payments and support for research and development, subject
to the attainment of certain product development milestone events and
satisfaction of other criteria to be agreed upon between the parties, of which
$15.6 million has been recognized through December 31, 1997. Eisai will receive
exclusive rights in Asia and Europe to develop and market resulting products
emerging from the collaboration, with the Company receiving royalties on
eventual product sales by Eisai. At any time, Eisai may terminate this agreement
by giving the Company 60 days' written notice based on a reasonable
determination that the products do not justify continued development or
marketing.
    
 
     Chugai Pharmaceutical Co., Ltd. In March 1996, the Company and Chugai
entered into a worldwide license agreement (co-exclusive with IDEC
Pharmaceuticals, Genentech and up to two additional companies) for the Company's
proprietary vector technology for high expression of recombinant proteins in
mammalian cells. As part of the agreement, Chugai paid an up-front licensing fee
of $4.5 million to the Company and will pay royalties on sales of Chugai
products manufactured using the technology.
 
     Boehringer Ingleheim GmbH. In December 1996, the Company and Boehringer
Ingleheim GmbH ("BI") entered into a worldwide license agreement (co-exclusive
with IDEC Pharmaceuticals, Genentech and up to two additional companies) for the
Company's proprietary gene expression technology (its "vector technology") for
high expression of recombinant proteins in mammalian cells. As part of the
agreement, BI paid an up-front licensing fee of $5.1 million to the Company and
will pay royalties on sales of BI products manufactured using the technology.
 
                                       22

<PAGE>   25
 
     Kirin Brewery Co., Ltd., Pharmaceutical Division. In December 1997, the
Company and Kirin Brewery Co., Ltd., Pharmaceutical Division ("Kirin") entered
into a worldwide license agreement (co-exclusive with IDEC Pharmaceuticals,
Genentech and up to two additional companies) for the Company's proprietary
vector technology for high expression of recombinant proteins in mammalian
cells. As part of the agreement, Kirin paid an up-front licensing fee of $6.3
million to the Company, which will be recognized in the first quarter of 1998,
and will pay royalties to the Company on sales of Kirin products manufactured
using the technology.
 
MANUFACTURING
 
     From its inception, the Company has focused on establishing and maintaining
a leadership position in cell culture techniques for antibody manufacturing.
Cell culture provides a method for manufacturing of clinical and commercial
grade protein products by reproducible techniques at various scales, up to many
kilograms of antibody. The Company's manufacturing facility is based on the
suspension culture of mammalian cells in stainless steel vessels. Suspension
culture fermentation provides greater flexibility and more rapid production of
the large amounts of antibodies required for pivotal trials than the bench-scale
systems that were previously utilized by the Company. During 1995, the Company
doubled the cell culture manufacturing capacity of its facility with the
installation of a second 2,750-liter production vessel that is supported by
existing upstream and downstream equipment. The Company's manufacturing facility
has been approved by the FDA only for the commercial manufacture of Rituxan and
may not be used for the commercial manufacture of other products. Additionally,
the Company is contractually required to manufacture Rituxan to capacity through
the end of 1999, and may not produce other products except in a separate
small-scale manufacturing area dedicated to the manufacture of clinical
materials (see "CMA" below). The Company estimates that, at full capacity, it
can produce within its facility enough Rituxan to treat approximately 25,000
patients per year at the approved dosage regime. See "-- Government Regulation."
 
     During 1997, the Company completed construction of a new clinical cell
culture manufacturing area ("CMA") within the Company's Torreyana facility. The
CMA should allow for the manufacture under cGMP regulations of proteins by the
Company to meet its current projected Phase I and Phase II requirements, but the
CMA will not allow for the clinical manufacture of the drug 9-AC.
 
   
     Because the Company's cell culture capacity is committed to the manufacture
of Rituxan for two years, it will not have the cell culture capacity to
manufacture commercial material for the Company's IDEC-Y2B8 and In2B8 products
during such period. The Company is currently accepting proposals for a qualified
commercial contractor to meet the long term manufacturing demands for IDEC-Y2B8
and In2B8. In addition, as the Company does not have expertise or facilities for
small molecule chemical manufacturing, the Company will need to establish a long
term manufacturing arrangement for 9-AC with an appropriate contract
manufacturer. The Company's 9-AC clinical materials requirements will be met
over the next two years by Pharmacia, as part of the product in-license
agreement. Additionally, as the Company does not have fill/finish expertise, the
Company will be dependent on outside contractors to meet its current and future
requirements for fill/finish. See "Risk Factors -- Limited Manufacturing
Experience."
    
 
     During 1998, the Company plans to manufacture Rituxan at its manufacturing
facility in San Diego, California. The Company anticipates that its facility in
San Diego should provide sufficient production capacity to meet clinical and
early commercial requirements of Rituxan. The Company is dependent upon
Genentech to fill/finish and meet long-term manufacturing demands for Rituxan
and SmithKline Beecham to fulfill all of the manufacturing requirements for
IDEC-CE9.1 and/or IDEC-151. Genentech is currently constructing additional
manufacturing capacity in part to satisfy long-term demands for Rituxan and
SmithKline Beecham has constructed a larger manufacturing plant for IDEC-CE9.1
and/or IDEC-151. The Company is considering the addition of another
manufacturing facility to meet its long-term requirements for additional
products under development.
 
     The Company has made its vector technology platform available for licensing
to a small number of other biopharmaceutical and pharmaceutical companies. In
March 1995, Genentech, one of the premier companies in recombinant DNA-based
production, became the first to license the Company's gene expression technology
for its own product development efforts. This technology has also been licensed
to Chugai, BI and Kirin.
 
                                       23

<PAGE>   26
 
SALES AND MARKETING
 
     During 1998, the Company will depend on the successful marketing and sales
of Rituxan for much of its anticipated revenue. Rituxan will be marketed and
sold in the United States pursuant to a co-promotion agreement with Genentech,
which currently has a sales and marketing staff of approximately 50
professionals that is largely dedicated to the commercialization of Rituxan. To
fulfill its duties under the co-promotion agreement, the Company has recently
created a marketing staff and a sales organization of 32 professionals with
experience primarily in the oncology therapeutic category, who will be dedicated
exclusively to the commercialization of Rituxan. The Company expects to add two
more employees to this staff in 1998. The Company will rely heavily on Genentech
to supply related marketing support services including customer service, order
entry, shipping and billing, customer reimbursement assistance, managed-care
sales support, medical information, and sales training. There can be no
assurance that the Company's sales and marketing staff will successfully
transition the Company into long-term profitability. Furthermore, there can be
no assurance that Genentech will successfully perform its role in the
co-promotion relationship.
 
     Commercialization of the Company's products is expensive and
time-consuming. The Company has adopted a strategy of pursuing collaborative
agreements with strategic partners that provide for co-promotion of certain of
the Company's products. To the extent that the Company elects to participate in
co-promotion efforts in the United States or Canada, and in those instances
where the Company retains exclusive marketing rights in specified territories,
the Company will need to maintain and expand its sales and marketing effort in
order to establish a successful direct sales capability in the targeted markets.
The Company will also need to build marketing support services including
customer service, order entry, shipping and billing, customer reimbursement
assistance, managed-care sales support, medical information and sales training.
There can be no assurance that the Company will be able to establish a
successful direct sales and marketing capability in any or all targeted markets
or that it will be successful in gaining market acceptance for its products. To
the extent that the Company has entered or in the future enters into
co-promotion or other licensing arrangements, any revenues received by the
Company will be dependent on the efforts of third parties and there can be no
assurance that such efforts will be successful. Failure to establish a sales
capability either in the United States or outside the United States may have a
material adverse effect on the Company. See "-- Sales and Marketing."
 
     Outside of the United States and Canada, the Company has adopted a strategy
to pursue collaborative arrangements with established pharmaceutical companies
for marketing, distribution and sale of its products. There can be no assurance
that any of these companies or their sublicensees will successfully market,
distribute or sell the Company's products or that the Company will be able to
establish and maintain successful co-promotion or distribution arrangements. See
"Risk Factors -- Patents and Proprietary Rights."
 
PATENTS AND PROPRIETARY TECHNOLOGY
 
     The biopharmaceutical field is characterized by a large number of patent
filings. A substantial number of patents have already been issued to other
biotechnology and biopharmaceutical companies. Particularly in the monoclonal
antibody field, competitors may have filed applications for or have been issued
patents and may obtain additional patents and proprietary rights relating to
products or processes competitive with or similar to those of the Company. To
date, no consistent policy has emerged regarding the breadth of claims allowed
in biopharmaceutical patents. Moreover, United States and foreign country patent
laws are distinct and the interpretations thereunder unique to each country.
Thus, patentability, validity and infringement issues for the same technology or
inventions may be resolved differently in different jurisdictions. There can be
no assurance that patents do not exist in the United States or in foreign
countries or that patents will not be issued that would have an adverse effect
on the Company's ability to market its products. Accordingly, the Company
expects that commercializing monoclonal antibody-based products may require
licensing and/or cross-licensing of patents with other companies in the field.
There can be no assurance that the licenses, which might be required for the
Company's processes or products, would be available on commercially acceptable
terms, if at all. The ability to license any such patents and the likelihood of
successfully contesting the scope or validity of such patents are uncertain and
the costs associated therewith may be significant. If the Company is
 
                                       24

<PAGE>   27
 
required to acquire rights to valid and enforceable patents but cannot do so at
a reasonable cost, the Company's ability to manufacture or market its products
would be materially adversely affected.
 
     IDEC Pharmaceuticals is the assignee of seven issued and 14 allowed U.S.
patents, 16 U.S. patent applications and numerous corresponding foreign patent
applications. Certain other patents and/or applications owned by third parties
have been exclusively licensed, as in the case of anti-gp39 core technology
licensed from Dartmouth College, or non-exclusively licensed by IDEC
Pharmaceuticals. The Company has filed trademark applications in the United
States, Canada and in certain international markets for the trademarks
"PRIMATIZED," "PROVAX," "Rituxan" and "IDEC Pharmaceuticals." "IDEC
Pharmaceuticals" and "PRIMATIZED" have been registered as trademarks in the
United States.
 
     The Company has allowed and pending U.S. patent applications and pending
foreign counterparts broadly directed to its pan-B antibody technology,
including Rituxan, and the radioimmunoconjugates, IDEC-Y2B8 and IDEC-In2B8. The
Company's radioimmunoconjugate products include a chelating agent covered by a
U.S. patent that is non-exclusively sublicensed to the Company. The Company has
been granted by the European Patent Office a patent covering Rituxan. Genentech,
IDEC Pharmaceuticals' collaborative partner for Rituxan, has secured an
exclusive license to a U.S. patent and counterpart foreign patent applications
assigned to Xoma Corporation ("Xoma"), that relate to chimeric antibodies
against the CD20 antigen. Genentech has granted IDEC Pharmaceuticals a
non-exclusive sublicense to make, have made, use and sell certain products,
including Rituxan, under such patents and patent applications. Genentech and the
Company will share any royalties due to Xoma in the Genentech/IDEC
Pharmaceuticals co-promotion territory.
 
     The Company has filed for worldwide patent protection on its PRIMATIZED
antibody technology. In August 1997, the Company received U.S. Patent No.
5,658,570 claiming the Company's PRIMATIZED antibodies. Three additional U.S.
patents claiming the PRIMATIZED antibody technology were allowed in 1997. These
patents and applications generically and specifically cover the Company's
PRIMATIZED antibody technology.
 
     PROVAX, the Company's antigen formulation, is the subject matter of two
issued U.S. patents, two allowed U.S. patents, one pending U.S. application and
pending foreign counterparts. In addition, U.S. and foreign patent applications
have been filed on aspects of the Company's proprietary high-yield gene
expression technology, including the Company's homologous recombination system.
The Company has been granted U.S. Patent No. 5,648,267 and has received a notice
of allowance on a U.S. patent claiming the high-yield gene expression
technology. In early 1998, the Company also received a Notice of Allowance for a
U.S. patent directed to its homologous recombination technology.
 
     In late 1997, the Company received Notices of Allowance for six U.S.
patents. The first is directed to a patent claiming the Company's anti-gp39
patent, IDEC-131, and the remaining five broadly claim the Company's anti-RSV
antibody technology. Foreign counterparts of these allowed patents are pending.
 
     The Company is aware of several third-party patents and patent applications
that, if successfully asserted against the Company, would affect the Company's
ability to make, use, offer to sell, sell and import its products. These
third-party patents and, patent applications include:
 
          (i) U.S. patent applications and foreign counterparts filed by
     Bristol-Myers Company that disclose antibodies to a B7 antigen;
 
          (ii) a U.S. patent assigned to Columbia University, which the Company
     believes has been exclusively licensed to Biogen, related to monoclonal
     antibodies to the 5C8 antigen found on T cells. The Company believes the
     5C8 antigen and gp39, the target for the Company's anti-gp39 antibodies and
     its collaboration with Eisai, may be the same protein expressed on the
     surface of T cells;
 
          (iii) a number of issued patents that relate to various aspects of
     radioimmunotherapy of cancer and to methods of treating patients with
     anti-CD4 antibodies; and
 
          (iv) three U.S. patents, assigned to Burroughs Wellcome, relating to
     therapeutic uses of CHO glycosylated antibodies.
 
                                       25

<PAGE>   28
 
     The owners, or licensees of the owners, of these patents may assert that
one or more of the Company's products infringe one or more claims of such
patents. Specifically, if legal action is commenced against the Company to
enforce any of these patents and the plaintiff in such action prevails, the
Company could be prevented from practicing the subject matter claimed in such
patents. In such event or under other appropriate circumstances, the Company may
attempt to obtain licenses to such patents. However, no assurance can be given
that any owner would license the patents to the Company, at all or on terms that
would permit commercialization of the Company's products using such technology.
An inability to commercialize such products would have a material adverse effect
on the Company's business, results of operations and financial condition.
 
     If the Company is required to enforce any of its patents, such enforcement
may require the use of substantial financial and human resources of the Company.
The Company may also have to participate in interference proceedings if declared
by the PTO to determine priority of invention, which typically take years to
resolve and could also result in substantial costs to the Company. Moreover,
should the Company need to defend against a patent lawsuit circumvent existing
patents, substantial delays and expense in product redesign and development or
significant legal expense and uncertainty in asserting non-infringement,
invalidity and/or unenforceability of any patent may also result. The Company
also relies upon unpatented trade secrets, and no assurance can be given that
others will not independently develop substantially equivalent proprietary
information and techniques or otherwise gain access to the Company's trade
secrets or disclose such technology, or that the Company can meaningfully
protect such rights.
 
     IDEC Pharmaceuticals requires its employees, consultants, outside
scientific collaborators and sponsored researchers and other advisers to execute
confidentiality agreements upon the commencement of employment or consulting
relationships with the Company. These agreements provide that all confidential
information developed or made known to the individual during the course of the
individual's relationship with IDEC Pharmaceuticals is to be kept confidential
and not disclosed to third parties except in specific circumstances. In the case
of employees of the Company, the agreement provides that all inventions
conceived by such employees shall be the exclusive property of the Company.
There can be no assurance, however, that these agreements will provide
meaningful protection or adequate remedies for the Company's trade secrets in
the event of unauthorized use or disclosure of such information.
 
COMPETITION
 
     The development of therapeutic agents for human disease is intensely
competitive. Many different approaches are being developed or have already been
adopted into routine use for the management of diseases targeted by the Company.
Competitive approaches to the Company's products include radioimmunotherapies
and antibody-drug and antibody-toxin conjugates for cancers, and
chemotherapeutic agents and various immunologically based agents for cancers and
autoimmune disorders. Ultimately, the Company believes that its products will be
competitive or complementary to existing products and other products still in
development. In some cases, the Company's products may be used along with other
agents in "combination therapies."
 
     Many of the Company's existing or potential competitors have substantially
greater financial, technical and human resources than the Company and may be
better equipped to develop, manufacture and market products. In addition, many
of these companies have extensive experience in preclinical testing and human
clinical trials. These companies may develop and introduce products and
processes competitive with or superior to those of the Company. The Company is
aware that certain other companies are in the process of clinical testing of
potentially competitive biotechnology-based products. If approved for the same
indications for which the Company is developing products, such products may make
it more difficult for the Company to obtain approval of its own products or
reduce the potential market shares for the Company's products.
 
     The Company's competition will be determined in part by the potential
indications for which the Company's antibodies are developed and ultimately
approved by regulatory authorities. For certain of the Company's potential
products, an important factor in competition may be the timing of market
introduction versus that of competitive products. Accordingly, the relative
speed with which the Company develops its products, completes the required
approval processes and generates and markets commercial product quantities
 
                                       26

<PAGE>   29
 
are expected to be important competitive factors. The Company expects that
competition among products approved for sale will be based, among other factors,
on product activity, safety, reliability, availability, price, patent position
and new usage and purchasing patterns established by managed care and other
group purchasing organizations.
 
     The Company's competitive position also depends upon its ability to attract
and retain qualified personnel, obtain patent protection or otherwise develop
proprietary products or processes, secure sufficient capital resources to
complete product development and regulatory processes, to build a marketing and
sales organization, and to build or obtain large-scale manufacturing facilities,
if required, beyond its facility in San Diego.
 
GOVERNMENT REGULATION
 
     The testing, manufacturing, labeling, advertising, promotion, export and
marketing, among other things, of the Company's product and proposed products
are subject to extensive regulation by governmental authorities in the United
States and other countries. In the United States, pharmaceutical products are
regulated by the FDA under the Federal Food, Drug, and Cosmetic Act and other
laws, including, in the case of biologics, the Public Health Service Act. At the
present time, with the exception of 9-AC, the Company believes that its products
will be regulated by the FDA as biologics. Biologics require the submission of a
BLA and approval by the FDA prior to being marketed in the United States. 9-AC,
which the Company believes will be regulated by the FDA as a drug, will require
the submission of an NDA and approval by the FDA prior to being marketed in the
United States. The regulatory approval process for an NDA is similar to the
approval process for a BLA. Manufacturers of biologics and drugs may also be
subject to state regulation.
 
     The steps required before a product may be approved for marketing in the
United States generally include (i) preclinical laboratory tests and animal
tests, (ii) the submission to the FDA of an IND for human clinical testing,
which must become effective before human clinical trials may commence, (iii)
adequate and well-controlled human clinical trials to establish the safety and
efficacy of the product, (iv) the submission to the FDA of a BLA or NDA, (v) FDA
review of the the BLA or NDA, and (vi) satisfactory completion of an FDA
inspection of the manufacturing facility or facilities at which the product is
made to assess compliance with cGMP. The testing and approval process requires
substantial time, effort, and financial resources and there can be no assurance
that any approval will be granted on a timely basis, if at all.
 
   
     Preclinical tests include laboratory evaluation of the product, as well as
animal studies to assess the potential safety and efficacy of the product. The
results of the preclinical tests, together with manufacturing information and
analytical data, are submitted to the FDA as part of an IND, which must become
effective before human clinical trials may be commenced. The IND will
automatically become effective thirty days after receipt by the FDA, unless the
FDA before that time raises concerns or questions about the conduct of the
trials as outlined in the IND. In such a case, the IND sponsor and the FDA must
resolve any outstanding concerns before clinical trials can proceed. There can
be no assurance that submission of an IND will result in FDA authorization to
commence clinical trials.
    
 
     Clinical trials involve the administration of the investigational product
to healthy volunteers or patients under the supervision of qualified principal
investigators. Further, each clinical study must be reviewed and approved by an
independent Institutional Review Board.
 
     Clinical trials typically are conducted in three sequential phases, but the
phases may overlap. In Phase I, the initial introduction of the drug into human
subjects, the drug is usually tested for safety (adverse effects), dosage
tolerance, absorption, metabolism, distribution, excretion and pharmacodynamics.
Phase II usually involves studies in a limited patient population to (i)
evaluate preliminarily the efficacy of the drug for specific, targeted
indications, (ii) determine dosage tolerance and optimal dosage and (iii)
identify possible adverse effects and safety risks. Phase III trials generally
further evaluate clinical efficacy and test further for safety within an
expanded patient population.
 
     In the case of products for severe or life-threatening diseases, the
initial human testing is sometimes done in patients rather than in healthy
volunteers. Since these patients are already afflicted with the target disease,
 
                                       27

<PAGE>   30
 
it is possible that such studies may provide evidence of efficacy traditionally
obtained in Phase II trials. These trials are frequently referred to as "Phase
I/II" trials. There can be no assurance that Phase I, Phase II or Phase III
testing will be completed successfully within any specific time period, if at
all, with respect to any of the Company's product candidates. Furthermore, the
FDA may suspend clinical trials at any time on various grounds, including a
finding that the subjects or patients are being exposed to an unacceptable
health risk.
 
     The results of the preclinical studies and clinical studies, together with
detailed information on the manufacture and composition of the product, are
submitted to the FDA in the form of a or BLA or NDA requesting approval to
market the product. Before approving a BLA or NDA, the FDA will inspect the
facilities at which the product is manufactured, and will not approve the
product unless cGMP compliance is satisfactory. The FDA may deny a BLA or NDA if
applicable regulatory criteria are not satisfied, require additional testing or
information, and/or require postmarketing testing and surveillance to monitor
the safety or efficacy of a product. There can be no assurance that FDA approval
of any BLA or NDA submitted by the Company will be granted on a timely basis or
at all. Also, if regulatory approval of a product is granted, such approval may
entail limitations on the indicated uses for which it may be marketed.
 
     As a general matter, data regarding, for example, partial tumor shrinkage,
can be developed in less time than survival data or recurrence data in clinical
trials of cancer therapies. In 1996, the FDA adopted a policy under which BLAs
or NDAs for cancer therapies may be submitted and considered for approval on the
basis of data from clinical trials showing, for example, partial tumor
shrinkage. Additionally, in November 1997, the Federal Food, Drug, and Cosmetic
Act was amended to codify certain FDA programs intended to expedite approval of
new drugs and biologics for the treatment of serious and life-threatening
diseases (the "FDCA Amendment"). In the past, the FDA has deemed cancer a
serious and life-threatening disease. It may therefore be possible under the
statutory amendments and the FDA's policy to submit a BLA or NDA for cancer
therapies on the basis of, for example, partial tumor shrinkage earlier than for
certain other types of drugs or biologics. There can be no assurance, however,
that the statutory amendments and the FDA's policy will be deemed to apply to
IDEC-Y2B8, 9-AC or any of the Company's other products, or that, if applicable,
the approval process will, in fact, be accelerated. Moreover, the accelerated
approval process does not necessarily increase the likelihood that any of the
Company's product candidates will be approved by the FDA.
 
     Additionally, the FDCA Amendment clarified that the FDA may, in certain
circumstances, approve a new drug or biologic on the basis of data from one
clinical study together with confirmatory scientific evidence obtained before or
after approval, rather than on the basis of data from two or more clinical
studies, as is ordinarily the case. It may therefore be possible, with the FDA's
concurrence, to submit a BLA or NDA for FDA approval on the basis of data from
one clinical study. There can be no assurance, however, that the FDA will apply
the statutory amendment to any BLA or NDA for IDEC-Y2B8, 9-AC or any of the
Company's other products, or that the FDA would approve such a BLA or NDA.
 
     Both before and after approval is obtained, violations of regulatory
requirements, including the preclinical and clinical testing process, the BLA or
NDA review process, or thereafter (including after approval) may result in
various adverse consequences, including the FDA's delay in approving or refusal
to approve a product, withdrawal of an approved product from the market, and/or
the imposition of criminal penalties against the manufacturer and/or BLA or NDA
holder. For example, BLA and NDA holders are required to report certain adverse
reactions to the FDA, and to comply with certain requirements concerning
advertising and promotional labeling for their products. Also, quality control
and manufacturing procedures must continue to conform to cGMP regulations after
approval, and the FDA periodically inspects manufacturing facilities to assess
compliance with cGMP. Accordingly, manufacturers must continue to expend time,
monies and effort in the area of production and quality control to maintain cGMP
compliance. In addition, discovery of problems may result in restrictions on a
product, manufacturer or BLA or NDA holder, including withdrawal of the product
from the market. Also, new government requirements may be established that could
delay or prevent regulatory approval of the Company's products under
development.
 
     The Company will also be subject to a variety of foreign regulations
governing clinical trials and sales of its products. Whether or not FDA approval
has been obtained, approval of a product by the comparable
 
                                       28

<PAGE>   31
 
regulatory authorities of foreign countries must be obtained prior to the
commencement of marketing of the product in those countries. The approval
process varies from country to country and the time may be longer or shorter
than that required for FDA approval. At least initially, the Company intends, to
the extent possible, to rely on foreign licensees to obtain regulatory approval
for marketing its products in foreign countries.
 
     Orphan Drug Designation.  Under the Orphan Drug Act, the FDA may grant
orphan drug designation to drugs intended to treat a "rare disease or
condition," which generally is a disease or condition that affects fewer than
200,000 individuals in the United States. Orphan drug designation must be
requested before submitting a BLA or NDA. After the FDA grants orphan drug
designation, the generic identity of the therapeutic agent and its potential
orphan use are publicly disclosed by the FDA. Orphan drug designation does not
convey any advantage in, or shorten the duration of, the regulatory review and
approval process. If a product which has an orphan drug designation subsequently
receives FDA approval for the indication for which it has such designation, the
product is entitled to orphan exclusivity, i.e., the FDA may not approve any
other applications to market the same drug for the same indication, except in
certain very limited circumstances, for a period of seven years.
 
   
     In 1994, the Company obtained orphan drug designation for Rituxan,
IDEC-Y2B8 and IDEC-In2B8 from the FDA to treat certain B-cell non-Hodgkin's
lymphomas (as defined on page 1). In connection with its approval by the FDA,
Rituxan has received orphan drug exclusivity in the United States. However,
there can be no assurance that IDEC-Y2B8 or IDEC-In2B8 will receive orphan drug
exclusivity for the B-cell non-Hodgkin's lymphoma indication, and it is possible
that competitors of the Company could obtain approval, and attendant orphan drug
exclusivity, for IDEC-Y2B8 or IDEC-In2B8 for the B-cell non-Hodgkin's lymphoma
indication, thus precluding the Company from marketing IDEC-Y2B8 or IDEC-In2B8
for that indication in the United States. In addition, even if the Company does
obtain orphan exclusivity for any of its compounds for B-cell non-Hodgkin's
lymphoma, there can be no assurance that competitors will not receive approval
of other, different drugs or biologics for B-cell non-Hodgkin's lymphoma.
Although obtaining FDA approval to market a product with orphan drug exclusivity
can be advantageous, there can be no assurance that the scope of protection or
the level of marketing exclusivity that is currently afforded by orphan drug
designation will remain in effect in the future.
    
 
PHARMACEUTICAL PRICING AND REIMBURSEMENT
 
     The future revenues and profitability of biopharmaceutical companies as
well as the availability of capital may be affected by the continuing efforts of
government and third party payors to contain or reduce costs of health care
through various means. In the United States, there have been, and the Company
expects that there will continue to be, a number of federal and state proposals
to implement governmental control on pharmaceutical pricing. While the Company
cannot predict whether any such legislative or regulatory proposals will be
adopted, the adoption of such proposals could have a material adverse effect on
the Company's business, financial condition or prospects. In addition, the
Company's ability to commercialize its products successfully will depend in part
on the extent which appropriate reimbursement levels for the cost of such
products and related treatment are obtained from governmental authorities,
private health insurers and other organizations, such as HMOs. Third party
payors are increasingly challenging the prices charged for medical products and
services. Also, the trend toward managed health care in the United States and
the concurrent growth of organizations such as HMOs, which could control or
significantly influence the purchase of health care services and products, as
well as legislative proposals to reform health care or reduce government
insurance programs may all result in lower prices for the Company's products.
The cost containment measures that health care payors and providers are
instituting and the effect of any health care reform could adversely affect the
Company's ability to sell its products and may have a material adverse effect on
the Company.
 
EMPLOYEES
 
     As of December 31, 1997, the Company employed 339 persons. The Company has
128 employees in research and development and 139 in manufacturing. In addition,
the Company retains approximately 100
 
                                       29

<PAGE>   32
 
independent contractors. None of the Company's employees are represented by a
labor union or bound by a collective bargaining agreement. Management believes
that its overall relations with its employees are good.
 
ENVIRONMENTAL REGULATION
 
     The Company's business involves the controlled use of hazardous materials,
chemicals and various radioactive compounds. Although the Company believes that
its safety procedures for handling and disposing of such materials comply with
the standards prescribed by state and federal regulations, the risk of
accidental contamination or injury from these materials cannot be completely
eliminated. In the event of such an accident, the Company could be held liable
for any damages that result and any such liability could exceed the resources of
the Company. The Company may incur substantial cost to comply with environmental
regulations. The Company anticipates no material capital expenditures to be
incurred for environmental compliance in fiscal year 1998. In addition, disposal
of radioactive materials used by the Company in its research efforts may only be
made at approved facilities. Approval of a site in California has been delayed
indefinitely. The Company currently stores such radioactive materials on site.
 

ITEM 2. PROPERTIES.
 
     IDEC Pharmaceuticals currently leases approximately 118,000 square feet of
administrative, laboratory, manufacturing and warehouse space at two locations
in San Diego, California. The Company's principal executive offices, primary
research facilities and manufacturing plant are located 11011 Torreyana Road in
San Diego, California. This facility is leased pursuant to a 15-year operating
lease which commenced in 1993. The Company has the option to extend the term of
the lease for two additional periods of five years each. In August 1996, the
Company entered into a seven-year operating lease for additional administrative
and warehouse space at 3030 Callan Road in San Diego, California. The Company
has the option to extend the term of the Callan Road lease for two additional
years.
 

ITEM 3. LEGAL PROCEEDINGS.
 
     (a) The Company is not a party to any material legal proceedings.
 
     (b) No material legal proceedings were terminated in the fourth quarter of
1997.
 

ITEM 4. SUBMISSION OF MATTERS TO A VOTE OF SECURITY HOLDERS.
 
     No matters were submitted to a vote of the Company's stockholders during
the last quarter of the year ended December 31, 1997.
 
                                       30

<PAGE>   33
 

                                    PART II
 

ITEM 5. MARKET FOR REGISTRANT'S COMMON EQUITY AND RELATED STOCKHOLDER MATTERS.
 
     (a) Market Information
 
     The Company's common stock trades on the Nasdaq National Market tier of The
Nasdaq Stock Market under the symbol "IDPH." The following table sets forth the
high and low sales price for the Company's Common Stock as reported by the
Nasdaq National Market for the years ended December 31, 1997 and 1996.
 

<TABLE>
<CAPTION>
                                                        COMMON STOCK PRICE
                                                        -------------------
                                                         HIGH         LOW
                                                        -------      ------
<S>                                                     <C>          <C>
Year ended December 31, 1997
  First Quarter.....................................      $30 3/4     $19 7/8
  Second Quarter....................................       27 1/8      15 3/4
  Third Quarter.....................................       42 7/16     23 3/8
  Fourth Quarter....................................       46 1/4      30 3/4
Year ended December 31, 1996
  First Quarter.....................................      $23 1/8     $15 7/8
  Second Quarter....................................       32 5/8      21
  Third Quarter.....................................       27 3/8      13 7/8
  Fourth Quarter....................................       26 3/8      18 1/8
</TABLE>

 
     (b) Holders
 
     As of January 30, 1998 there were approximately 425 stockholders of record
of the Company's Common Stock.
 
     (c) Dividends
 
     The Company has not paid dividends since its inception. The Company
currently intends to retain all earnings, if any, for use in the expansion of
its business and therefore does not anticipate paying any dividends in the
foreseeable future.
 
     (d) Recent Sales of Unregistered Securities.
 
     None
 
                                       31

<PAGE>   34
 

ITEM 6. SELECTED FINANCIAL DATA.
 
     The selected consolidated financial data presented below under the captions
"Consolidated Statement of Operations Data" and "Consolidated Balance Sheet
Data" for, and as of the end of, each of the years in the five-year period ended
December 31, 1997, are derived from the consolidated financial statements of the
Company, which consolidated financial statements have been audited by KPMG Peat
Marwick LLP, independent certified public accountants. The consolidated
financial statements as of December 31, 1996 and 1997, and for each of the years
in the three-year period ended December 31, 1997, and the report thereon, are
included elsewhere in this Form 10-K. The information set forth below is not
necessarily indicative of the results of future operations and should be read in
conjunction with the Consolidated Financial Statements and related Notes thereto
that are included in this Prospectus and with "Management's Discussion and
Analysis of Financial Condition and Results of Operations."
 

<TABLE>
<CAPTION>
                                                             YEARS ENDED DECEMBER 31,
                                                ---------------------------------------------------
                                                  1993       1994       1995      1996       1997
                                                --------   --------   --------   -------   --------
                                                     (IN THOUSANDS, EXCEPT PER SHARE AMOUNTS)
<S>                                             <C>        <C>        <C>        <C>       <C>
CONSOLIDATED STATEMENT OF OPERATIONS DATA:
Revenues:
  Revenues from unconsolidated joint
     business.................................  $     --   $     --   $     --   $    --   $  9,266
  Contract revenues...........................     4,329      5,143     12,136    15,759     11,840
  License fees................................     8,385      2,300     11,500    14,250     23,500
                                                --------   --------   --------   -------   --------
          Total revenues......................    12,714      7,443     23,636    30,009     44,606
Operating expenses:
  Manufacturing costs.........................        --         --         --        --     18,875
  Research and development....................    18,723     21,191     22,488    28,147     32,407
  Selling, general and administrative.........     4,262      4,768      6,112     7,298     11,320
  Acquired technology rights..................        --         --     11,437        --         --
                                                --------   --------   --------   -------   --------
          Total operating expenses............    22,985     25,959     40,037    35,445     62,602
                                                --------   --------   --------   -------   --------
Loss from operations..........................   (10,271)   (18,516)   (16,401)   (5,436)   (17,996)
Interest income (expense), net................     1,174        485       (891)      481      2,572
Other income (expense)........................       215         --         --        --       (114)
Convertible preferred stock dividends.........        --         --         --      (696)        --
                                                --------   --------   --------   -------   --------
Net loss applicable to common stock...........  $ (8,882)  $(18,031)  $(17,292)  $(5,651)  $(15,538)
                                                ========   ========   ========   =======   ========
Net loss per share............................  $   (.96)  $  (1.65)  $  (1.18)  $  (.34)  $   (.83)
Shares used in computing net loss per
  common share................................     9,265     10,931     14,650    16,573     18,739
</TABLE>

 

<TABLE>
<CAPTION>
                                                                    DECEMBER 31,
                                                  -------------------------------------------------
                                                   1993      1994      1995       1996       1997
                                                  -------   -------   -------   --------   --------
                                                      (IN THOUSANDS, EXCEPT PER SHARE AMOUNTS)
<S>                                               <C>       <C>       <C>       <C>        <C>
CONSOLIDATED BALANCE SHEET DATA:
Cash, cash equivalents and securities
  available-for-sale............................  $26,503   $20,601   $24,010   $ 78,727   $ 69,657
Total assets....................................   50,728    45,494    47,626    113,029    106,013
Notes payable...................................    4,697    11,062     9,846      8,845      7,794
Total stockholders' equity......................   35,674    27,896    31,169     92,614     80,679
</TABLE>

 
                                       32

<PAGE>   35
 

ITEM 7. MANAGEMENT'S DISCUSSION AND ANALYSIS OF FINANCIAL CONDITION AND RESULTS
OF OPERATIONS.
 
   
     The following discussion should be read in conjunction with the
Consolidated Financial Statements and related Notes thereto of IDEC
Pharmaceuticals appearing elsewhere in this Form 10-K.
    
 
OVERVIEW
 
     IDEC Pharmaceuticals is primarily engaged in the commercialization and
research and development of targeted therapies for the treatment of cancer and
autoimmune and inflammatory diseases. In November 1997, the Company received
approval from the FDA to market its first product, Rituxan, in the United States
and Hoffmann-LaRoche, the Company's European marketing partner, received
marketing clearance for Rituxan from the Swiss regulatory body, the Office
Intercantonal de Controle de Medicaments. Rituxan is being co-promoted in the
United States under a joint business arrangement with Genentech, with the
Company receiving a share of the pretax co-promotion operating results. Under
the terms of separate agreements with Genentech, commercialization of Rituxan
outside the United States will be the responsibility of Hoffmann-LaRoche, except
in Japan where Zenyaku will be responsible for product development, marketing
and sales. The Company will receive royalties on Rituxan sales outside the
United States.
 
     Revenues for the Company consists of revenues from the unconsolidated joint
business with Genentech, contract revenues and license fees. To date a
substantial portion of the Company's revenues have been derived from contract
revenues and license fees and the Company anticipates that revenues from
unconsolidated joint business will comprise an increasing portion of total
revenues in the future resulting from the commercialization of Rituxan.
 
   
     Revenues from unconsolidated joint business consists of the Company's share
of the pretax operating results generated from its joint business arrangement
with Genentech, revenue from bulk Rituxan sales to Genentech and reimbursement
from Genentech of the Company's sales force and development expenses. Revenues
also include royalty income from Hoffmann-LaRoche and Zenyaku on sales of
Rituxan outside the United States. Under the joint business arrangement, all
U.S. sales of Rituxan and associated expenses will be recognized by Genentech
with the Company recording its share of the pretax operating results on a
quarterly basis, as defined in the Company's collaborative agreement with
Genentech. "Pretax operating results" under the joint business arrangement are
derived by taking the net U.S. sales of Rituxan to third-party customers less
costs of sales, third-party royalty expenses, distribution, selling and
marketing expenses and joint development expenses by the Company and Genentech.
    
 
     Contract revenues consist of non-refundable research and development
funding under collaborative agreements with the Company's various strategic
partners and other funding under contractual arrangements with other parties.
Contract research and development funding generally compensates the Company for
discovery, preclinical and clinical expenses related to the collaborative
development programs for certain products of the Company.
 
     License fees consist of non-refundable fees from product development
milestone payments, the sale of license rights to the Company's propriety gene
expression technology and non-refundable fees from the sale of product rights
under collaborative development and license agreements with the Company's
strategic partners.
 
     The Company is obligated to manufacture and supply bulk Rituxan to
Genentech through the end of 1999 with an option to continue supplying Rituxan
thereafter. The cost of bulk Rituxan sold to Genentech is recorded as
manufacturing cost in the Company's consolidated statements of operations. Under
the Company's collaborative agreement with Genentech, the sales price of bulk
Rituxan sold to Genentech is capped at a price which is currently less than the
Company's cost to manufacture bulk Rituxan. See "Risk Factors -- Limited Sales
and Marketing Experience."
 
     The Company has incurred increasing annual operating expenses and, with the
commercialization of Rituxan, the Company expects such trends to continue. The
Company has incurred annual operating losses since its inception in 1985, and
the transition of the Company to profitability will be dependent upon the
commercial success of Rituxan. As of December 31, 1997, the Company had an
accumulated deficit of $99.4 million. See "Risk Factors -- History of Operating
Losses; Accumulated Deficit."
 
                                       33

<PAGE>   36
 
RESULTS OF OPERATIONS
 
     YEARS ENDED DECEMBER 31, 1997 AND 1996
 
     Revenues from Unconsolidated Joint Business. The Company earned revenues
from unconsolidated joint business for the first time in 1997. Revenues from
unconsolidated joint business totaled $9.3 million in 1997 and consists of $10.6
million of bulk Rituxan sales to Genentech, $3.0 million in reimbursement for
the Company's sales force and development expenses for Rituxan from Genentech
and the Company's share of the joint business operating loss equaling $4.3
million. During 1997, the joint business recorded an operating loss due to
significant shared expenses related to the product launch of Rituxan in the
United States in December 1997. Rituxan sales to third-party customers recorded
by Genentech totaled $5.5 million, which amounted to net sales of $5.1 million
after returns and allowances. The $5.1 million of net sales of Rituxan were
driven in part by pre-existing demand for Rituxan upon launch in December 1997.
The Company anticipates that revenues from unconsolidated joint business will
continue to increase in the near term due to the commercialization of Rituxan.
 
   
     Contract Revenues. Contract revenues totaled $11.8 million in 1997 compared
to $15.8 million in 1996. The decrease in contract revenues in 1997 was
primarily due to the completion of funding in 1996 under the Company's
collaborative development agreement with Mitsubishi.
    
 
     License Fees. License fees totaled $23.5 million in 1997 compared to $14.3
million in 1996. The increase in license fees in 1997 was primarily due to a
$15.0 million product development milestone payment received from Genentech upon
FDA approval of Rituxan. License fee revenues can vary significantly from year
to year based upon the consummation of new corporate alliances and the
achievement of product development milestone events. The Company continues to
pursue other collaborative and license arrangements; however, no assurance can
be given that discussions in this regard will result in any such arrangements or
that the Company will receive significant revenues from any such collaborative
or license arrangements.
 
     Manufacturing Costs. The Company incurred manufacturing costs for the first
time in 1997. Manufacturing costs totaled $18.9 million in 1997 and consisted of
manufacturing costs related to production of bulk Rituxan sold to Genentech and
includes costs of approximately $2.0 million incurred for the start-up of the
Company's manufacturing facility. The Company expects to continue incurring
substantial additional manufacturing costs as the Company continues to
manufacture bulk Rituxan.
 
   
     Research and Development. Research and development expenses totaled $32.4
million in 1997 compared to $28.1 million in 1996. The increase in research and
development expenses in 1997 was primarily due to a $3.0 million up-front
licensing fee to Pharmacia for exclusive rights to 9-AC, a broad spectrum
anti-cancer agent, a license fee payment for anti-MIF antibody technology
rights, contract manufacturing expenses for IDEC-Y2B8 in preparation for a Phase
III trial in 1998 and higher facility expenses. Research and development
expenses in 1997 were partially offset by the utilization of the Company's
manufacturing facility for bulk production of Rituxan inventory in 1997 compared
to research and development manufacturing production in 1996 of clinical
material used for clinical trials. The Company expects to continue incurring
substantial additional research and development expenses in the future, due to
expansion of research and development programs; technology inlicensing and
regulatory-related expenses; preclinical and clinical testing of the Company's
various products under development; and production scale-up and manufacturing of
products used in clinical trials.
    
 
     Selling, General and Administrative. Selling, general and administrative
expenses totaled $11.3 million in 1997 compared to $7.3 million in 1996. The
increase in selling, general and administrative expenses in 1997 was primarily
due to the creation of a sales and marketing infrastructure, expenses resulting
from the commercial launch of Rituxan and higher personnel expenses to support
expanded manufacturing operations. Selling, general and administrative expenses
necessary to support expanded manufacturing capacity, expanded clinical trials,
research and development and the potential expansion of the sales and marketing
organization are expected to increase in the foreseeable future.
 
     Interest Income/Expense. Net interest income totaled $2.6 million in 1997
compared to $.5 million in 1996. The increase in net interest income in 1997 was
due to higher average balances in cash, cash equivalents
 
                                       34

<PAGE>   37
 
and securities available-for-sale, a decrease in noncash interest charges for
common stock warrants issued in connection with certain debt financings and a
decrease in interest expense due to lower balances in notes payable.
 
     Income Taxes. IDEC Pharmaceuticals has incurred losses on an annualized
basis since inception; therefore, no provision for income taxes has been
recorded. The Company's net operating loss carryforwards available to offset
future taxable income at December 31, 1997 are approximately $82.0 million for
federal income tax purposes and expire between 1999 and 2012. The future
utilization of net operating loss carryforwards may be limited under the
Internal Revenue Code ("IRC") due to an IRC defined ownership change that
occurred during 1991. However, the Company believes that such limitations will
not have a material impact upon the utilization of the net operating loss
carryforwards.
 
     YEARS ENDED DECEMBER 31, 1996 AND 1995
 
     Contract Revenues. Contract revenues totaled $15.8 million in 1996 compared
to $12.1 million in 1995. The increase in contract revenues in 1996 was
primarily due to revenue from a collaboration entered into with Eisai in
December 1995, revenue from a one-time contract manufacturing and cell line
development arrangement with OraVax, Inc. and ongoing efforts under existing
collaborative agreements with Genentech and Seikagaku, offset by decreased
revenues from SmithKline Beecham as a result of the planned transfer of clinical
development of IDEC-CE9.1 to SmithKline Beecham in late 1995.
 
     License Fees. License fees totaled $14.3 million in 1996 compared to $11.5
million in 1995. License fees in 1996 include $4.5 million received for the
license to Chugai of the Company's gene expression technology, $4.0 million
received from SmithKline Beecham for the initiation of a Phase III trial by
SmithKline Beecham of IDEC-CE9.1, $4.0 million from Genentech for the expansion
of its collaboration with the Company and for the achievement of a product
development milestone event for Rituxan and license fee revenues received from
Seikagaku and Eisai also for the achievement of product development milestone
events.
 
   
     Research and Development. Research and development expenses totaled $28.1
million in 1996 compared to $22.5 million in 1995. The increase in research and
development expenses in 1996 was primarily due to a $1.3 million expense for
access to certain patent rights related to Rituxan, increased personnel expenses
related to the completion of the Phase III trial, preparation of the Biologics
License Application and the preparation for building of Rituxan commercial
inventory.
    
 
   
     Selling, General and Administrative. Selling, general and administrative
expenses totaled $7.3 million in 1996 compared to $6.1 million in 1995. Selling,
general and administrative expenses increased in 1996 due to higher personnel
expenses to support expanded manufacturing operations, completion of the Phase
III trial and preparation of the Biologics License Applications for Rituxan.
    
 
     Acquired Technology Rights. In March 1995, the Company issued 1,000,000
shares of its Common Stock and 69,375 shares of its 10% Series B Nonvoting
Cumulative Convertible Preferred Stock for the repurchase of all Merrill
Lynch/Morgan Stanley, L.P. rights in the Company's lymphoma products. In the
first quarter of 1995, the Company recorded a non-cash charge of $11.4 million,
representing the purchase of the acquired technology rights.
 
     Interest Income/Expense. Net interest income totaled $.5 million in 1996
compared to net interest expense of $.9 million in 1995. The increase in net
interest income in 1996 from net interest expense in 1995 was due to higher
balances in cash, cash equivalents and securities available-for-sale, offset by
an increase in interest expense resulting from increases in notes payable used
to finance certain capital purchases and an increase in non-cash interest
charges for certain common stock warrants issued in connection with certain debt
financings.
 
LIQUIDITY AND CAPITAL RESOURCES
 
     The Company has financed its operating and capital expenditures since
inception principally through the sale of equity securities, contract revenues,
license fees, lease financing transactions and interest income. The Company
expects to finance its current and planned operating requirements principally
through cash on hand,
 
                                       35

<PAGE>   38
 
funds from its joint business arrangement with Genentech and with funds from
existing collaborative agreements and contracts which the Company believes will
be sufficient to meet its near-term operating requirements. The Company believes
that its cash, cash equivalents and securities available-for-sale, together with
cash generated from its existing agreements, contracts and joint business
arrangement, will be sufficient to finance the Company's currently anticipated
needs for operating and capital expenditures for the foreseeable future.
Existing agreements and contracts, however, could be canceled by the contracting
parties. In addition, the Company may, from time to time, seek additional
funding through a combination of new collaborative agreements, strategic
alliances and additional equity and debt financings or from other sources. There
can be no assurance that such additional funds can be obtained through these
sources on acceptable terms, if at all. If adequate funds are not available from
the joint business arrangement, operations or additional sources of financing,
the Company's business could be materially and adversely affected.
 
   
     The Company's working capital and capital requirements will depend upon
numerous factors, including: the progress of the Company's preclinical and
clinical testing; fluctuating or increasing manufacturing requirements, research
and development programs; timing and expense of obtaining regulatory approvals;
levels of resources that the Company devotes to the development of
manufacturing, sales and marketing capabilities; technological advances; status
of competitors; and the ability of the Company to establish collaborative
arrangements with other organizations.
    
 
     Until required for operations, the Company's policy under established
guidelines is to keep its cash reserves in bank deposits, certificates of
deposit, commercial paper, corporate notes, United States government instruments
and other readily marketable debt instruments, all of which are investment-grade
quality.
 
   
     At December 31, 1997, the Company had $69.7 million in cash, cash
equivalents and securities available-for-sale compared to cash, cash equivalents
and securities available-for-sale of $78.7 million at December 31, 1996. Sources
of cash, cash equivalents and securities available-for-sale during 1997 include
$3.5 million from the issuance of common stock under employee stock option and
employee stock purchase plans and $3.0 million from funding under a loan to
finance equipment purchases. Uses of cash, cash equivalents and securities
available-for-sale during 1997 include $2.8 million used in operations, $5.9
million used to purchase capital equipment, a $3.0 million preferred equity
investment in CNI and $4.1 million used to pay notes payable.
    
 
     In September 1997, the Company entered into an agreement with a financial
institution under which the Company purchased in a private transaction a capped
call option, exercisable only at maturity, representing the Company's right to
purchase from the financial institution up to 600,000 shares of the Company's
Common Stock. The Company has the right to settle the capped call option by
receiving cash or stock. The capped call option which the Company purchased is
expected to be settled, if exercised, with cash paid to the Company in an amount
equal to the difference between the strike price and the market price, subject
to caps which will limit the total amount of cash the Company could receive.
 
     Simultaneously, with its purchase of the capped call option, the Company
sold to the same financial institution a call option, exercisable only at
maturity, entitling the financial institution to purchase from the Company up to
900,000 shares of the Company's Common Stock at a certain strike price per
share. The Company has the right to settle the call option with cash or stock
and, if exercised, the Company expects to settle the call option by issuing up
to 900,000 shares of the Company's Common Stock to the financial institution.
The financial institution has advised the Company that it has engaged, and may
continue to engage, in transactions, including buying and selling shares of the
Company's Common Stock, to offset its risk relating to the call option, which
could affect the market price of the Company's Common Stock.
 
     In September 1997, the Company and CNI entered into a development and
license agreement for the development of inflammatory and autoimmune disease
products based upon CNI's anti-MIF antibody technology and a stock purchase
agreement providing for certain equity investments in CNI by the Company. Under
the terms of these agreements, the Company may make payments totaling up to
$10.5 million, subject to the attainment of certain product development
milestone events. Additionally, the Company will pay CNI royalties on sales by
the Company of any products emerging from the collaboration. In 1997 the Company
made a $3.0 million preferred equity investment in CNI.
 
                                       36

<PAGE>   39
 
   
     Under the terms of the 9-AC asset transfer agreement, the Company may make
payments to Pharmacia totaling up to $16.0 million, subject to the attainment of
certain product development milestone events. No royalties are payable to
Pharmacia on sales by the Company of any commercialized products emerging from
the agreement. The Company anticipates achieving a product development milestone
event in 1999 that would result in the Company making a $6.0 million payment to
Pharmacia.
    
 
     In August 1995, the Company completed receipt of funding under a $10.0
million lease financing agreement to finance both equipment and facility
improvements. Terms of the financing agreement require final principal payments
of $1.1 million and $.4 million in July 1998 and January 1999, respectively.
 
NEW ACCOUNTING STANDARDS
 
   
     In June 1997, the Financial Accounting Standards Board ("FASB") issued
Statement of Financial Accounting Standards No. 130 "Reporting Comprehensive
Income" ("Statement No. 130"). Statement No. 130 establishes standards for
reporting and display of comprehensive income and its components (revenue,
expenses, gains and losses) in a full set of general-purposes financial
statements. Statement No. 130 shall be effective for fiscal years beginning
after December 15, 1997 and requires reclassification of earlier periods
presented. The Company does not believe the adoption of Statement No. 130 will
have a significant impact on the Company's results of operations or financial
position for the year ending December 31, 1998.
    
 
   
     In June 1997, the FASB issued Statement of Financial Accounting Standards
No. 131, "Disclosures about Segments of an Enterprise and Related Information"
("Statement No. 131"), effective for fiscal years beginning after December 15,
1997. Statement No. 131 establishes standards for reporting information about
operating segments in annual financial statements and selected information about
operating segments in interim financial reports issued to stockholders. The
Company does not believe the adoption of Statement No. 131 will have a
significant impact on the Company's consolidated financial statement
disclosures.
    
 
YEAR 2000 COMPLIANCE
 
     Many currently installed computer systems and software products are coded
to accept only two digit entries in the date code field. Beginning in the year
2000, these date code fields will need to accept four digit entries to
distinguish 21st century dates from 20th century dates. As a result, in less
than two years, computer systems and/or software used by many companies may need
to be upgraded to comply with such "Year 2000" requirements.
 
   
     Management has initiated its Year 2000 Program, which has already
identified several manufacturing software systems that are not yet Year 2000
compliant. The Company expects to complete its audit by the end of February and
intends to complete its third-party confirmations and begin its remedial phase
by the end of the third quarter of 1998. While the Company has begun evaluating
potential strategies for resolving Year 2000 problems, the dollar amount that
the Company will spend to remediate its Year 2000 issues remains uncertain, and
management has not yet assessed the Year 2000 compliance expenses and related
potential effect on the Company's operations. The Company expects to incur
internal personnel expenses as well as consulting and other expenses related to
the infrastructure and facilities enhancements necessary to prepare the
Company's systems for the year 2000.
    
 
     The Company anticipates its Year 2000 Program will be completed before
January 1, 2000. However, there can be no assurance that the Year 2000 Program,
or computer systems and applications of other companies on which the Company's
operations rely, will be timely converted, or that any such failure to convert
by another company would not have a material adverse effect on the Company's
systems. Moreover, a failure to correct any non-compliant manufacturing software
could disable the Company's manufacturing capacity, resulting in inventory and
product shortages and ultimately creating higher manufacturing costs for the
Company. See "Risk Factors -- Limited Manufacturing Experience."
 

I
TEM 7A. QUANTITATIVE AND QUALITATIVE DISCLOSURES ABOUT MARKET RISK.
 
     The information required by this item is omitted because it is not
required.
 
                                       37

<PAGE>   40
 

ITEM 8. CONSOLIDATED FINANCIAL STATEMENTS AND SUPPLEMENTARY DATA:
 
                IDEC PHARMACEUTICALS CORPORATION AND SUBSIDIARY
 
                          CONSOLIDATED BALANCE SHEETS
                                 (IN THOUSANDS)
 

<TABLE>
<CAPTION>
                                                                 DECEMBER 31,
                                                              -------------------
                                                                1996       1997
                                                              --------   --------
<S>                                                           <C>        <C>
ASSETS
Current assets:
  Cash and cash equivalents.................................  $ 25,337   $ 34,847
  Securities available-for-sale.............................    53,390     34,810
  Contract revenue receivables, net.........................     3,635      3,971
  Due from related party, net...............................       732          -
  Inventories...............................................     4,384      4,134
  Prepaid expenses and other current assets.................     3,337      1,431
                                                              --------   --------
     Total current assets...................................    90,815     79,193
Property and equipment, net.................................    21,453     23,449
Investment and other assets.................................       761      3,371
                                                              --------   --------
                                                              $113,029   $106,013
                                                              ========   ========
 
LIABILITIES AND STOCKHOLDERS' EQUITY
Current liabilities:
  Current portion of notes payable..........................  $  3,830   $  3,908
  Accounts payable..........................................     3,106      1,626
  Accrued expenses..........................................     5,951      6,382
  Due to related party, net.................................         -        870
  Deferred revenue..........................................         -      6,646
                                                              --------   --------
     Total current liabilities..............................    12,887     19,432
                                                              --------   --------
Notes payable, less current portion.........................     5,015      3,886

Deferred rent...............................................     1,513      2,016
Due to related party, noncurrent............................     1,000          -
Commitments
Stockholders' equity:
  Convertible preferred stock, $.001 par value, 8,000 shares
     authorized; 330 shares and 245 shares issued and
     outstanding at December 31, 1996 and 1997,
     respectively; $26,938 and $19,225 liquidation value at
     December 31, 1996 and 1997, respectively...............         -          -
  Common stock, $.001 par value, 50,000 shares authorized;
     18,059 shares and 19,356 shares issued and outstanding
     at December 31, 1996 and 1997, respectively............        18         19
  Additional paid-in capital................................   176,448    179,956
  Unrealized gains (losses) on securities
     available-for-sale.....................................       (37)        57
  Accumulated deficit.......................................   (83,815)   (99,353)
                                                              --------   --------
     Total stockholders' equity.............................    92,614     80,679
                                                              --------   --------
                                                              $113,029   $106,013
                                                              ========   ========
</TABLE>

 
          See accompanying notes to consolidated financial statements.
 
                                       38

<PAGE>   41
 
                IDEC PHARMACEUTICALS CORPORATION AND SUBSIDIARY
 
                     CONSOLIDATED STATEMENTS OF OPERATIONS
                     (IN THOUSANDS, EXCEPT PER SHARE DATA)
 
   

<TABLE>
<CAPTION>
                                                                 YEARS ENDED DECEMBER 31,
                                                              -------------------------------
                                                                1995       1996        1997
                                                              --------    -------    --------
<S>                                                           <C>         <C>        <C>
Revenues:
  Revenues from unconsolidated joint business...............  $     --    $    --    $  9,266
  Contract revenues.........................................    12,136     15,759      11,840
  License fees..............................................    11,500     14,250      23,500
                                                              --------    -------    --------
          Total revenues (including related party revenues
            of $5,500 and $27,373 in 1996 and 1997,
            respectively)...................................    23,636     30,009      44,606
Operating expenses:
  Manufacturing costs.......................................        --         --      18,875
  Research and development..................................    22,488     28,147      32,407
  Selling, general and administrative.......................     6,112      7,298      11,320
  Acquired technology rights................................    11,437         --          --
                                                              --------    -------    --------
          Total operating expenses..........................    40,037     35,445      62,602
                                                              --------    -------    --------
Loss from operations........................................   (16,401)    (5,436)    (17,996)
                                                              --------    -------    --------
Other income (expense):
  Interest income...........................................     1,387      3,178       3,489
  Interest expense..........................................    (2,278)    (2,697)       (917)
  Other.....................................................        --         --        (114)
                                                              --------    -------    --------
          Total other income (expense)......................      (891)       481       2,458
                                                              --------    -------    --------
Net loss....................................................   (17,292)    (4,955)    (15,538)
Convertible preferred stock dividends.......................        --       (696)         --
                                                              --------    -------    --------
Net loss applicable to common stock.........................  $(17,292)   $(5,651)   $(15,538)
                                                              ========    =======    ========
Net loss per common share...................................  $  (1.18)   $ (0.34)   $  (0.83)
Shares used in computing net loss per common share..........    14,650     16,573      18,739
</TABLE>

    
 
          See accompanying notes to consolidated financial statements.
 
                                       39

<PAGE>   42
 
                IDEC PHARMACEUTICALS CORPORATION AND SUBSIDIARY
 
                CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY
                                 (IN THOUSANDS)
 

<TABLE>
<CAPTION>
                               CONVERTIBLE
                             PREFERRED STOCK    COMMON STOCK    ADDITIONAL      UNREALIZED GAINS                        TOTAL
                             ---------------   --------------    PAID-IN     (LOSSES) ON SECURITIES   ACCUMULATED   STOCKHOLDERS'
                             SHARES   AMOUNT   SHARES  AMOUNT    CAPITAL       AVAILABLE-FOR-SALE       DEFICIT        EQUITY
                             ------   ------   ------  ------   ----------   ----------------------   -----------   -------------
<S>                          <C>      <C>      <C>     <C>      <C>          <C>                      <C>           <C>
Balance at December 31,
  1994.....................    --      $ --    13,728   $14      $ 89,464             $(14)            $(61,568)      $ 27,896
Issuance of common stock
  under stock option and
  employee stock purchase
  plans....................    --        --       230    --           953               --                   --            953
Issuance of series A-1 and
  A-2 convertible preferred
  stock pursuant to terms
  of a collaborative
  agreement................   138        --        --    --         7,149               --                   --          7,149
Issuance of common stock
  and series B convertible
  preferred stock to
  acquire technology
  rights...................    69        --     1,000     1        11,436               --                   --         11,437
Issuance of common stock
  for services.............    --        --       103    --           322               --                   --            322
Amortization of fair value
  change in common stock
  warrants.................    --        --        --    --           680               --                   --            680
Change in unrealized gains
  (losses) on securities
  available-for-sale.......    --        --        --    --            --               24                   --             24
Net loss...................    --        --        --    --            --               --              (17,292)       (17,292)
                              ---      ----    ------   ---      --------             ----             --------       --------
Balance at December 31,
  1995.....................   207        --    15,061    15       110,004               10              (78,860)        31,169
Issuance of common stock
  under stock option and
  employee stock purchase
  plans....................    --        --       342    --         1,304               --                   --          1,304
Issuance of common stock in
  public offering..........    --        --     2,070     2        46,275               --                   --         46,277
Issuance of common stock
  for services.............    --        --        17    --           359               --                   --            359
Issuance of common stock
  from exercise of stock
  warrants.................    --        --       569     1         4,754               --                   --          4,755
Issuance of series A-3 and
  series A-6 convertible
  preferred stock pursuant
  to terms of a
  collaborative
  agreement................   123        --        --    --        12,500               --                   --         12,500
Amortization of fair value
  change in common stock
  warrants.................    --        --        --    --         1,252               --                   --          1,252
Change in unrealized gains
  (losses) on securities
  available-for-sale.......    --        --        --    --            --              (47)                  --            (47)
Net loss...................    --        --        --    --            --               --               (4,955)        (4,955)
                              ---      ----    ------   ---      --------             ----             --------       --------
Balance at December 31,
  1996.....................   330        --    18,059    18       176,448              (37)             (83,815)        92,614
Issuance of common stock
  under stock option and
  employee stock purchase
  plans....................    --        --       670     1         3,508               --                   --          3,509
Issuance of common stock
  from exercise of stock
  warrants.................    --        --       105    --            --               --                   --             --
Issuance of common stock
  from conversion of series
  A-1 and B convertible
  preferred stock..........   (85)       --       522    --            --               --                   --             --
Change in unrealized gains
  (losses) on securities
  available-for-sale.......    --        --        --    --            --               94                   --             94
Net loss...................    --        --        --    --            --               --              (15,538)       (15,538)
                              ---      ----    ------   ---      --------             ----             --------       --------
Balance at December 31,
  1997.....................   245      $ --    19,356   $19      $179,956             $ 57             $(99,353)      $ 80,679
                              ===      ====    ======   ===      ========             ====             ========       ========
</TABLE>

 
          See accompanying notes to consolidated financial statements.
 
                                       40

<PAGE>   43
 
                IDEC PHARMACEUTICALS CORPORATION AND SUBSIDIARY
 
                     CONSOLIDATED STATEMENTS OF CASH FLOWS
                                 (IN THOUSANDS)
 

<TABLE>
<CAPTION>
                                                                 YEARS ENDED DECEMBER 31,
                                                             --------------------------------
                                                               1995        1996        1997
                                                             --------    --------    --------
<S>                                                          <C>         <C>         <C>
Cash flows from operating activities:
  Net loss.................................................  $(17,292)   $ (4,955)   $(15,538)
  Adjustments to reconcile net loss to net cash used in
     operating activities:
     Depreciation and amortization.........................     2,401       2,643       4,010
     Deferred rent.........................................       450         390         503
     Other non-cash expenses...............................        --        (104)       (131)
     Gains (losses) on sales of securities
       available-for-sale..................................         5          --         (12)
     Acquired technology rights............................    11,437          --          --
     Issuance of common stock for services.................       322         359          --
     Amortization of fair value change in common stock
       warrants............................................       680       1,252          --
     Change in assets and liabilities:
       Contract revenue receivables, net...................      (621)     (3,712)       (336)
       Due from related party, net.........................        --        (732)        732
       Inventories.........................................        --      (4,384)        250
       Prepaid expenses and other assets...................       403         890       2,296
       Accounts payable, accrued expenses and other
          liabilities......................................     1,650       3,570      (1,049)
       Due to related party................................        --       1,000        (130)
       Deferred revenue....................................    (2,024)         --       6,646
                                                             --------    --------    --------
          Net cash used in operating activities............    (2,589)     (3,783)     (2,759)
                                                             --------    --------    --------
Cash flows from investing activities:
  Purchase of marketable securities and securities
     available-for-sale....................................    (8,218)    (72,771)    (39,538)
  Sales and maturities of marketable securities and
     securities available-for-sale.........................    10,715      25,265      58,224
  Purchase of property and equipment.......................    (1,315)     (6,301)     (5,875)
  Investment in Cytokine Networks, Inc.....................        --          --      (3,000)
                                                             --------    --------    --------
          Net cash provided by (used in) investing
            activities.....................................     1,182     (53,807)      9,811
                                                             --------    --------    --------
Cash flows from financing activities:
  Proceeds from notes payable..............................     2,500       2,475       3,003
  Payments on notes payable................................    (4,058)     (3,440)     (4,054)
  Proceeds from issuance of common stock, net..............       953      52,564       3,509
  Proceeds from issuance of convertible preferred stock,
     net...................................................     7,149      12,500          --
                                                             --------    --------    --------
          Net cash provided by financing activities........     6,544      64,099       2,458
                                                             --------    --------    --------
Net increase in cash and cash equivalents..................     5,137       6,509       9,510
Cash and cash equivalents, beginning of year...............    13,691      18,828      25,337
                                                             --------    --------    --------
Cash and cash equivalents, end of year.....................  $ 18,828    $ 25,337    $ 34,847
                                                             ========    ========    ========
Supplemental disclosure of cash flow information --
  Cash paid during the year for interest...................  $  1,518    $  1,469    $    952
</TABLE>

 
          See accompanying notes to consolidated financial statements.
                                       41

<PAGE>   44
 
                IDEC PHARMACEUTICALS CORPORATION AND SUBSIDIARY
 
                   NOTES TO CONSOLIDATED FINANCIAL STATEMENTS
 
NOTE 1: ORGANIZATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES
 
     Business: IDEC Pharmaceuticals Corporation (the "Company") is primarily
engaged in the commercialization and research and development of targeted
therapies for the treatment of cancer and autoimmune and inflammatory diseases.
 
     Principles of Consolidation: The consolidated financial statements include
the financial statements of IDEC Pharmaceuticals Corporation and its wholly
owned subsidiary IDEC Seiyaku. All significant intercompany balances and
transactions have been eliminated in consolidation.
 
     Cash and Cash Equivalents: For the purposes of financial statement
presentation, the Company considers all highly liquid investments in debt
securities with original maturities of three months or less to be cash
equivalents.
 
     Securities Available-for-Sale: Securities available-for-sale are carried at
fair value, with unrealized gains and losses, net of tax, reported as a separate
component of stockholders' equity. The cost of securities sold is based on the
specific identification method.
 
     Inventories: Inventories are stated at the lower of cost or market. Cost is
determined in a manner which approximates the first-in, first-out ("FIFO")
method. Inventories at December 31, 1997 and 1996 consists of the following
(table in thousands):
 

<TABLE>
<CAPTION>
                                                      1996      1997
                                                     ------    ------
<S>                                                  <C>       <C>
Raw materials......................................  $  366    $1,204
Work in process....................................      --       486
Finished goods.....................................   4,018     2,444
                                                     ------    ------
                                                     $4,384    $4,134
                                                     ======    ======
</TABLE>

 
     Property and Equipment: Property and equipment are stated at cost.
Depreciation of property and equipment is calculated using the straight-line
method over the estimated useful lives of the assets, generally ranging from
three to seven years. Amortization of leasehold improvements is calculated using
the straight-line method over the shorter of the lease term or the estimated
useful lives of the assets.
 
     Fair Value of Financial Instruments: The carrying amount of cash and cash
equivalents, securities available-for-sale, contract revenue receivables,
accounts payable, accrued expenses and notes payable are considered to be
representative of their respective fair values because of the short-term nature
of those investments. A reasonable estimate of fair value is not practicable for
the liability, due to related party, at December 31, 1997, because of the
inherent difficulty of evaluating the timing of the payments.
 
     Research and Development: All research and development expenses, including
purchased research and development, are expensed in the period incurred.
Clinical grant expenses are fully accrued upon patient enrollment.
 
     Revenues from Unconsolidated Joint Business: Revenues from unconsolidated
joint business consists of the Company's share of the pretax operating results
generated from its joint business arrangement with Genentech, Inc.
("Genentech"), revenue from bulk Rituxan sales to Genentech, reimbursement from
Genentech of the Company's sales force and development expenses and royalty
income from F. Hoffmann-La Roche Ltd. ("Hoffmann-La Roche") and Zenyaku Kogyo
Co., Ltd. ("Zenyaku") on sales of Rituxan outside the United States and Canada.
Revenue from bulk Rituxan sales is recognized when accepted by Genentech. Under
the joint business arrangement, all U.S. sales of Rituxan and associated
expenses will be recorded in the books and accounts of Genentech with the
Company recording it's share of the pretax operating results on a quarterly
basis, as defined in the Company's collaborative agreement with Genentech (Note
7). Pretax operating results under the joint business arrangement are derived by
taking the net U.S. sales of Rituxan to
 
                                       42

<PAGE>   45
                IDEC PHARMACEUTICALS CORPORATION AND SUBSIDIARY
 
             NOTES TO CONSOLIDATED FINANCIAL STATEMENTS (CONTINUED)
 
third-party customers less cost of sales, third party royalty expenses,
distribution, selling and marketing expenses and joint development expenses by
the Company and Genentech.
 
     Contract Revenues: Contract revenues consist of non-refundable research and
development funding under collaborative agreements with the Company's various
strategic partners and other funding under contractual arrangements with other
parties. Contract research and development funding generally compensates the
Company for discovery, preclinical and clinical expenses related to the
collaborative development programs for certain products of the Company and is
recognized at the time research and development activities are performed under
the terms of the collaborative agreements. Contract revenues earned in excess of
contract payments received are classified as contract revenue receivables.
 
     License Fees: License fees consist of non-refundable fees from product
development milestone payments, the sale of license rights to the Company's
propriety gene expression technology and non-refundable fees from the sale of
product rights under collaborative development and license agreements with the
Company's strategic partners. Revenues from product development milestone
payments are recognized when the results or events stipulated in the agreement
have been achieved. License fee payments received in excess of amounts earned
are classified as deferred revenue.
 
     Manufacturing Costs: Manufacturing costs consist of manufacturing costs
related to the production of bulk Rituxan sold to Genentech.
 
     Stock Based Compensation: The Company's stock option and purchase plans are
accounted for under Accounting Principles Board Opinion No. 25, "Accounting for
Stock Issued to Employees" ("APB Opinion No. 25"), and the Company makes pro
forma footnote disclosures of the Company's operating results as if the Company
had adopted the fair value method under Financial Accounting standards Board
Statement No. 123, "Accounting for Stock-Based Compensation" ("Statement No.
123").
 
     Income Taxes: Income taxes are accounted for under the asset and liability
method where deferred tax assets and liabilities are recognized for the future
tax consequences attributable to differences between the financial statement
carrying amounts of existing assets and liabilities and their respective tax
bases and net operating loss and tax credit carryforwards. Deferred tax assets
and liabilities are measured using enacted tax rates expected to apply to
taxable income in the years in which those temporary differences are expected to
be recovered or settled. The effect on deferred tax assets and liabilities of a
change in tax rates is recognized in income in the period that includes the
enactment date.
 
     Net Loss Per Common Share: In December 1997, the Company adopted Statement
of Financial Accounting Standards No. 128 "Earnings per Share" ("Statement No.
128"). Statement No. 128 supersedes Accounting Principles Board Opinion No. 15
("APB No. 15") and replaces "primary" and "fully diluted" earnings per share
("EPS") under APB No. 15 with "basic" and "diluted" EPS. Unlike primary EPS,
basic EPS excludes the dilutive effects of options, warrants and other
convertible securities. Diluted EPS reflects the potential dilution of
securities that could share in the earnings of the Company, similar to fully
diluted EPS. The adoption of Statement No. 128 did not have a material effect on
the Company's net loss per common share for the prior years presented. Options,
warrants and other convertible securities totaling 2,855,000 shares, 4,538,000
shares and 4,181,000 shares were excluded from the computations of net loss per
common share for the years ended December 31, 1995, 1996 and 1997, respectively,
as their effect is antidilutive.
 
     Use of Estimates: Management of the Company has made a number of estimates
and assumptions relating to the reporting of assets and liabilities and the
disclosure of contingent assets and liabilities at the date of the consolidated
financial statements and the reported amounts of revenues and expenses during
the reporting periods to prepare these consolidated financial statements in
conformity with generally accepted accounting principles. Actual results could
differ from these estimates.
 
                                       43

<PAGE>   46
                IDEC PHARMACEUTICALS CORPORATION AND SUBSIDIARY
 
             NOTES TO CONSOLIDATED FINANCIAL STATEMENTS (CONTINUED)
 
     Reclassifications: The prior year balances in preferred stock, common stock
and additional paid-in capital have been reclassified to effect the change in
par value to $.001 per share resulting from stockholder approval in May 1997, of
a change in the state of incorporation of the Company from the State of
California to the State of Delaware. Certain other balances in 1996 and 1995
have been reclassified to conform with the presentation in 1997.
 
NOTE 2: SECURITIES AVAILABLE-FOR-SALE
 
     Securities available-for-sale at December 31, 1996 and 1997 consist of the
following (tables in thousands):
 

<TABLE>
<CAPTION>
                                                                          1996
                                                    ------------------------------------------------
                                                                   GROSS         GROSS
                                                    AMORTIZED    UNREALIZED    UNREALIZED    MARKET
                                                      COSTS        GAINS         LOSSES       VALUE
                                                    ---------    ----------    ----------    -------
<S>                                                 <C>          <C>           <C>           <C>
Corporate securities..............................   $40,227        $  3          $(38)      $40,192
Commercial paper..................................     9,979          --            --         9,979
Certificates of deposit...........................     1,499          --            --         1,499
U.S. government agencies..........................     1,722          --            (2)        1,720
                                                     -------        ----          ----       -------
                                                     $53,427        $  3          $(40)      $53,390
                                                     =======        ====          ====       =======
</TABLE>

 

<TABLE>
<CAPTION>
                                                                          1997
                                                    ------------------------------------------------
                                                                   GROSS         GROSS
                                                    AMORTIZED    UNREALIZED    UNREALIZED    MARKET
                                                      COSTS        GAINS         LOSSES       VALUE
                                                    ---------    ----------    ----------    -------
<S>                                                 <C>          <C>           <C>           <C>
Corporate securities..............................   $13,672        $  3          $(18)      $13,657
Commercial paper..................................     4,707          44            --         4,751
Certificates of deposit...........................     5,699          --            --         5,699
U.S. government agencies..........................    10,675          29            (1)       10,703
                                                     -------        ----          ----       -------
                                                     $34,753        $ 76          $(19)      $34,810
                                                     =======        ====          ====       =======
</TABLE>

 
     The net unrealized holding gain (loss) on securities available-for-sale
included as a separate component of stockholders' equity at December 31, 1996
and 1997 totaled $(37,000) and $57,000, respectively. The gross realized gains
on sales of securities available-for-sale for the year ended December 31, 1997
totaled $12,000.
 
     The amortized cost and estimated fair value of securities
available-for-sale at December 31, 1997, by contractual maturity are shown below
(table in thousands):
 

<TABLE>
<CAPTION>
                                                         AMORTIZED    ESTIMATED
                                                           COST       FAIR VALUE
                                                         ---------    ----------
<S>                                                      <C>          <C>
Due in one year or less................................   $30,105      $30,170
Due after one year through two years...................     2,648        2,640
Due after ten years....................................     2,000        2,000
                                                          -------      -------
                                                          $34,753      $34,810
                                                          =======      =======
</TABLE>

 
                                       44

<PAGE>   47
                IDEC PHARMACEUTICALS CORPORATION AND SUBSIDIARY
 
             NOTES TO CONSOLIDATED FINANCIAL STATEMENTS (CONTINUED)
 
NOTE 3: PROPERTY AND EQUIPMENT
 
     Property and equipment at December 31, 1996 and 1997 consists of the
following (table in thousands):
 

<TABLE>
<CAPTION>
                                                            1996       1997
                                                           -------    -------
<S>                                                        <C>        <C>
Furniture and fixtures...................................  $ 1,158    $ 1,226
Machinery and equipment..................................   11,061     13,118
Leasehold improvements...................................   16,359     18,922
Construction in progress.................................    1,480      2,667
                                                           -------    -------
                                                            30,058     35,933
Accumulated depreciation and amortization................   (8,605)   (12,484)
                                                           -------    -------
                                                           $21,453    $23,449
                                                           =======    =======
</TABLE>

 
NOTE 4: NOTES PAYABLE
 
     Notes payable at December 31, 1996 and 1997, consist of the following
(table in thousands):
 

<TABLE>
<CAPTION>
                                                               1996       1997
                                                              -------    -------
<S>                                                           <C>        <C>
Prime plus 1% note (9.5% at December 31, 1997), due in
  monthly installments with a final payment of $750 due at
  maturity in 1998, secured by equipment, lease deed of
  trust, and a patent and trademark collateral assignment...   $2,710    $ 1,361
17.74% note, due in monthly installments with a final
  payment of $375 due at maturity in 1998, secured by
  equipment, lease deed of trust, and a patent and trademark
  collateral assignment.....................................    1,355        682
17.53% note, due in monthly installments with a final
  payment of $375 due at maturity in 1999, secured by
  equipment, lease deed of trust, and a patent and trademark
  collateral assignment.....................................    1,745      1,149
 9.32% to 10.62% capital lease obligations, due in monthly
  installments, maturing 2000...............................    2,263      1,831
 8.94% note, due in monthly installments, maturing 2001,
  secured by equipment......................................       --      2,771
Other notes, due in monthly installments, maturing through
  1997, secured by equipment................................      772         --
                                                              -------    -------
                                                                8,845      7,794
Current portion.............................................   (3,830)    (3,908)
                                                              -------    -------
                                                              $ 5,015    $ 3,886
                                                              =======    =======
</TABLE>

 
     Machinery and equipment recorded under capital leases was $2,698,000, net
of accumulated depreciation of $1,188,000 at December 31, 1997.
 
     The aggregate maturities of notes payable for each of the three years
subsequent to December 31, 1997, are as follows: 1998, $3,908,000; 1999,
$1,709,000; 2000, $1,470,000; and 2001, $707,000.
 
NOTE 5: 401(K) EMPLOYEE SAVINGS PLAN
 
     The Company has a qualified 401(k) Employee Savings Plan ("401(k) Plan"),
available to substantially all employees over the age of 21. The Company may
make discretionary contributions to the 401(k) Plan, which fully vest after four
years of service by the employee. There were no discretionary contributions for
the years ended December 31, 1997, 1996 and 1995.
 
                                       45

<PAGE>   48
                IDEC PHARMACEUTICALS CORPORATION AND SUBSIDIARY
 
             NOTES TO CONSOLIDATED FINANCIAL STATEMENTS (CONTINUED)
 
NOTE 6: RESEARCH AND DEVELOPMENT
 
     In December 1995, the Company and Eisai Co. Ltd. ("Eisai") entered into a
collaborative development agreement and a license agreement aimed at the
development and commercialization of humanized and PRIMATIZED anti-gp39
antibodies. Under the terms of these agreements, Eisai may provide up to
$37,500,000 in product development milestone payments and support for research
and development. Eisai will receive exclusive rights in Asia and Europe to
develop and market resulting products emerging from the collaboration, with the
Company receiving royalties on eventual product sales by Eisai. Eisai may
terminate these agreements based on a reasonable determination that the products
do not justify continued product development or marketing. Included in contract
revenues for 1995, 1996 and 1997 is $2,500,000, $5,500,000 and $2,750,000,
respectively, to fund product development, which approximates the research and
development expenses incurred under the program. Included in license fees for
the years ended December 31, 1995, 1996 and 1997, is $2,000,000, $750,000 and
$2,000,000, respectively, earned under these agreements.
 
     In December 1994, the Company and Seikagaku Corporation ("Seikagaku")
entered into a collaborative development agreement and a license agreement aimed
at the development and commercialization of a PRIMATIZED anti-CD23 antibody.
Under the terms of these agreements, Seikagaku may provide up to $26,000,000 in
product development milestone payments and support for research and development.
The Company and Seikagaku will share co-exclusive, worldwide rights to all
products emerging from the collaboration, with the Company receiving royalties
on eventual product sales by Seikagaku. Seikagaku may terminate these agreements
based on a reasonable determination that the products do not justify continued
product development or marketing. Included in contract revenues for 1995, 1996
and 1997 is $2,500,000, $3,500,000 and $3,500,000, respectively, to fund product
development, which approximates the research and development expenses incurred
under the program. Included in license fees for the years ended December 31,
1995, 1996 and 1997, is $1,000,000, $1,000,000 and $1,500,000, respectively,
earned under these agreements.
 
   
     In November 1993, the Company entered into a collaborative development
agreement and a license agreement with Mitsubishi Chemical Corporation
("Mitsubishi Chemical"), for the development of a PRIMATIZED anti-B7 antibody.
Under the terms of the collaboration, Mitsubishi may provide up to $12,185,000
in product development milestone payments and support for research and
development. The Company retained certain marketing rights and will receive
royalties on sales by Mitsubishi Chemical of any products commercialized
emerging from the collaboration. Mitsubishi Chemical may terminate the license
agreement if certain development objectives are not attained. The development
agreement with Mitsubishi expired on December 31, 1996. Included in contract
revenues for 1995 and 1996 is $2,047,000, and $2,000,000, respectively, to fund
product development, which approximates the research and development expenses
incurred under the program. Included in license fees for the year ended December
31, 1995 is $1,000,000 earned under these agreements.
    
 
     In October 1992, the Company and SmithKline Beecham p.1.c. ("SmithKline
Beecham") entered into a collaborative research and license agreement aimed at
the development and commercialization of therapeutic products based on the
Company's PRIMATIZED anti-CD4 antibodies. Under the terms of the agreement, the
Company will receive aggregate payments that have the potential of reaching in
excess of $60,000,000, subject to the attainment of certain product development
milestone events. The Company will receive funding for anti-CD4 related research
and development programs, royalties and a share of co-promotion profits (in
North America) on sales of products which may be commercialized as a result of
the agreement. SmithKline Beecham may terminate this agreement based on a
reasonable determination that the products do not justify continued development
or marketing. Included in contract revenues for 1995, 1996 and 1997 is
$3,488,000, $416,000 and $867,000 to fund product development, which
approximates the research and development expenses incurred under the program.
Included in license fees for the year ended December 31, 1996 is $4,000,000
earned under the agreement.
 
                                       46

<PAGE>   49
                IDEC PHARMACEUTICALS CORPORATION AND SUBSIDIARY
 
             NOTES TO CONSOLIDATED FINANCIAL STATEMENTS (CONTINUED)
 
     The Company performed research under certain other contracts and,
accordingly, realized revenues and recognized expenses in the accompanying
consolidated statements of operations.
 
NOTE 7: RELATED PARTY ARRANGEMENTS
 
     In March 1995, the Company and Genentech entered into a collaborative
agreement for the clinical development and commercialization of the Company's
anti-CD20 monoclonal antibody, Rituxan, for the treatment of non-Hodgkin's
B-cell lymphomas. Concurrent with the collaborative agreement the Company and
Genentech also entered into an expression technology license agreement for a
proprietary gene expression technology developed by the Company and a preferred
stock purchase agreement providing for certain equity investments in the Company
by Genentech (Note 8). Under the terms of these agreements, the Company may
receive payments totaling $58,500,000, subject to the attainment of certain
product development milestone events. Additionally, the Company may be
reimbursed by Genentech for certain other development and regulatory approval
expenses under the terms of the collaborative agreement. Genentech may terminate
this agreement for any reason. Included in contract revenues for 1995, 1996 and
1997 is $1,083,000, $1,500,000 and $2,389,000, respectively, to fund specific
product development, which approximates the research and development expenses
incurred under the program. Included in license fees for the years ended
December 31, 1995, 1996 and 1997, is $5,500,000, $4,000,000 and $15,000,000,
respectively, earned under these agreements.
 
     In addition, the Company and Genentech are co-promoting Rituxan in the
United States under a joint business arrangement, with the Company receiving a
share of the pretax operating results. During 1997, the joint business recorded
an operating loss due to significant shared expenses related to the product
launch of Rituxan in the United States in December 1997. Additionally, the
Company has a contractual obligation to manufacture and supply Rituxan through
the end of 1999 with an option to continue supplying Rituxan thereafter. Under
the Company's collaborative agreement with Genentech, the sales price of bulk
Rituxan sold to Genentech is capped at a price which is currently less than the
Company's cost to manufacture bulk Rituxan. Included in inventories at December
31, 1997, is $2,444,000 of bulk Rituxan inventory that will be sold to
Genentech. Revenues from unconsolidated joint business, as described in Note 1,
for the year ended December 31, 1997, consist of the following (table in
thousands):
 

<TABLE>
<S>                                                          <C>
Bulk Rituxan sales.........................................  $10,631
Reimbursement of selling and development expenses..........    2,985
Co-promotion operating loss................................   (4,350)
                                                             -------
                                                             $ 9,266
                                                             =======
</TABLE>

 
   
     Under the terms of separate agreements with Genentech, commercialization of
Rituxan outside the United States will be the responsibility of Hoffmann-La
Roche, except in Japan where Zenyaku will be responsible for product
development, marketing and sales. The Company will receive royalties on sales
outside the United States. Additionally, the Company will receive royalties on
sales of Genentech products manufactured using the Company's proprietary gene
expression system.
    
 
   
     In June 1991, the Company and Zenyaku entered into a product rights
agreement and a stock purchase agreement under which the Company granted Zenyaku
a license to manufacture, use and sell certain products for cancer and
autoimmune therapeutic applications. In November 1995, the Company and Zenyaku
terminated the product rights agreement and concurrently the Company, Zenyaku
and Genentech entered into a joint development, supply and license agreement
where Zenyaku received exclusive rights to develop, market and sell Rituxan in
Japan which resulted in the Company recognizing $2,000,000 in license fees from
Zenyaku.
    
 
                                       47

<PAGE>   50
                IDEC PHARMACEUTICALS CORPORATION AND SUBSIDIARY
 
             NOTES TO CONSOLIDATED FINANCIAL STATEMENTS (CONTINUED)
 
NOTE 8: STOCKHOLDERS' EQUITY
 
     Convertible Preferred Stock: In March 1995, the Company issued 1,000,000
shares of its common stock and 69,375 shares of its ten percent Series B
Nonvoting Cumulative Convertible Preferred Stock ("Series B Preferred Stock")
for the repurchase of all Merrill Lynch/Morgan Stanley, L.P. ("ML/MS") rights in
the Company's lymphoma products. The stock issuances resulted in a non-cash
charge to operating expenses in 1995 of $11,437,000, representing the purchase
of the acquired technology rights. In March 1997, the Series B Preferred Stock
and accrued dividends were converted into 367,000 shares of the Company's common
stock.
 
Additionally, the Company issued 100,000 shares of its Series A-1 Nonvoting
Convertible Preferred Stock ("Series A-1 Preferred Stock") in April 1995, and
37,521 shares of its Series A-2 Nonvoting Convertible Preferred Stock ("Series
A-2 Preferred Stock") in August 1995, 22,993 shares of its Series A-3 Nonvoting
Convertible Preferred Stock ("Series A-3 Preferred Stock") in March 1996,
100,000 shares of its Series A-6 Nonvoting Convertible Preferred Stock ("Series
A-6 Preferred Stock") in May 1996, to Genentech pursuant to the terms of a
preferred stock purchase agreement. The preferred stock purchase agreement was
entered into concurrently with a collaboration agreement as described in Note 7.
The Series A-1 Preferred Stock, Series A-2 Preferred Stock, Series A-3 Preferred
Stock and Series A-6 Preferred Stock have a liquidation preference per share of
$50, $67, $217 and $75, respectively, net of issuance costs. Each share of
Series A-1 Preferred Stock, Series A-2 Preferred Stock and Series A-3 Preferred
Stock is convertible at any time into ten shares of the Company's common stock
and each share of Series A-6 Preferred Stock is convertible at any time into
approximately 2.16 shares of the Company's common stock. In December 1997,
16,000 shares of Series A-1 Preferred Stock were converted into 155,000 shares
of the Company's common stock.
 
     Common Stock: In May 1996, the stockholders approved an increase in the
number of authorized common shares to 50,000,000 shares. In June 1996, the
Company completed a public offering of 2,070,000 shares of its common stock
resulting in net proceeds of $46,277,000. In March 1995, the Company issued
1,000,000 shares of its common stock for the repurchase of all ML/MS rights in
the Company's lymphoma products, see "Convertible Preferred Stock" above.
 
     In September 1997, the Company entered into an agreement with a financial
institution under which the Company purchased in a private transaction a capped
call option, exercisable only at maturity, representing the Company's right to
purchase from the financial institution up to 600,000 shares of the Company's
common stock. The Company has the right to settle the capped call option by
receiving cash or stock. The capped call option which the Company purchased is
expected to be settled, if exercised, with cash paid to the Company in an amount
equal to the difference between the strike price and the market price, subject
to caps which will limit the total amount of cash the Company could receive.
 
     Simultaneously, with its purchase of the capped call option, the Company
sold to the same financial institution a call option, exercisable only at
maturity, entitling the financial institution to purchase from the Company up to
900,000 shares of the Company's common stock at a certain strike price per
share. The Company has the right to settle the call option with cash or stock
and, if exercised, the Company expects to settle the call option by issuing up
to 900,000 shares of the Company's common stock to the financial institution.
The financial institution has advised the Company that it has engaged, and may
further engage, in transactions, including buying and selling shares of the
Company's common stock, to offset its risk relating to the call option, which
could affect the market price of the Company's common stock.
 
     Stockholder Rights Agreement: In July 1997, the Company's Board of
Directors declared a dividend of one preferred stock purchase right ("Right")
for each outstanding share of the Company's common stock. Each Right represents
the right to purchase one one-thousandth of a share of Series X Junior
Participating Preferred Stock at an exercise price of $200, subject to
adjustment, and will be exercisable only if a person or group acquires 15% or
more of the Company's common stock or announces a tender offer for 15% or more
of the Company's common stock. If a person acquires 15% or more of Company's
common stock all
 
                                       48

<PAGE>   51
                IDEC PHARMACEUTICALS CORPORATION AND SUBSIDIARY
 
             NOTES TO CONSOLIDATED FINANCIAL STATEMENTS (CONTINUED)
 
Rightsholders, except the acquiring person, will be entitled to buy shares of
the Company's common stock at a discount. Each Series X Junior Participating
Preferred share will be entitled to an aggregate dividend of 1,000 times the
dividend declared per share of common stock. The Board of Directors may
terminate the Rights Plan at any time or redeem the Rights at $.001 per Right,
prior to the time a person acquires more than 15% of the Company's common stock.
The Rights will expire in July 2007.
 
     Stock Option Plans: The Company has two active stock option plans.
 
     The 1988 Employee Stock Option Plan (the "Option Plan") was approved by the
stockholders in 1988 and has been subsequently amended. Under the Option Plan,
options for the purchase of the Company's common stock may be granted to key
employees (including officers), directors and outside consultants. Options may
be designated as incentive stock options or as nonqualified stock options and
generally vest over four years, except under a provision of the Option Plan
which allows accelerated vesting under certain conditions. Options under the
Option Plan, which have a term of up to ten years, are exercisable at a price
per share not less than the fair market value (85 percent of fair market value
for nonqualified options) on the date of grant. The aggregate number of shares
authorized for issuance under the Option Plan is 5,480,000.
 
     In September 1993, the Company adopted the 1993 Non-Employee Directors
Stock Option Plan (the "Directors Plan"), which was approved by the stockholders
in May 1994 and was subsequently amended. A total of 250,000 shares of common
stock are reserved for issuance to individuals who serve as non-employee members
of the Board of Directors. Options under the Directors Plan, which have a term
of up to ten years, are exercisable at a price per share not less than the fair
market value on the date or grant.
 
     A summary of the status of the Company's two active stock option plans as
of December 31, 1995, 1996 and 1997 and changes during the years ended on those
dates is presented below (table in thousands, except per share amounts):
 

<TABLE>
<CAPTION>
                                           DIRECTORS PLAN                 OPTION PLAN
                                     --------------------------    --------------------------
                                               WEIGHTED AVERAGE              WEIGHTED AVERAGE
                                     SHARES     EXERCISE PRICE     SHARES     EXERCISE PRICE
                                     ------    ----------------    ------    ----------------
<S>                                  <C>       <C>                 <C>       <C>
Outstanding at December 31, 1994...    35           $ 5.63         2,346          $ 2.96
  Granted..........................    70             3.38           311            3.90
  Exercised........................   (10)            5.63          (157)           4.07
  Canceled.........................   (10)            2.38           (33)           5.58
                                      ---           ------         -----          ------
Outstanding at December 31, 1995...    85             4.15         2,467            2.97
  Granted..........................    35            19.13         1,443           20.79
  Exercised........................   (10)            4.00          (172)           2.43
  Canceled.........................    (5)           19.13          (196)          10.10
                                      ---           ------         -----          ------
Outstanding at December 31, 1996...   105             8.45         3,542            9.86
  Granted..........................    83            27.41           815           26.27
  Exercised........................   (15)            9.04          (533)           4.26
  Canceled.........................    (5)           22.50           (43)          18.74
                                      ---           ------         -----          ------
Outstanding at December 31, 1997...   168           $17.31         3,781          $14.09
                                      ===           ======         =====          ======
</TABLE>

 
                                       49

<PAGE>   52
                IDEC PHARMACEUTICALS CORPORATION AND SUBSIDIARY
 
             NOTES TO CONSOLIDATED FINANCIAL STATEMENTS (CONTINUED)
 
     The following table summarizes information about the Directors Plan and the
Option Plan options outstanding as of December 31, 1997 (table in thousands,
except year and per share amounts):
 

<TABLE>
<CAPTION>
                                OPTIONS OUTSTANDING                       OPTIONS EXERCISABLE
                 -------------------------------------------------   ------------------------------
                               WEIGHTED AVERAGE
   RANGE OF        NUMBER         REMAINING       WEIGHTED AVERAGE     NUMBER      WEIGHTED AVERAGE
EXERCISE PRICES  OUTSTANDING   CONTRACTUAL LIFE    EXERCISE PRICE    EXERCISABLE    EXERCISE PRICE
- ---------------  -----------   ----------------   ----------------   -----------   ----------------
<S>              <C>           <C>                <C>                <C>           <C>
Directors Plan:
$2.38 -- $19.13     90,000           7.26              $ 8.35           90,000          $ 8.35
22.50 --  38.25     77,500           9.32               27.72           77,500           27.72
 
Option Plan:
$0.88 -- $ 2.56    663,917           5.55              $ 2.35          567,494          $ 2.32
 3.00 --   3.00    699,116           6.70                3.00          647,081            3.00
 3.25 --  18.00    488,291           7.35                8.87          226,785            6.30
20.13 --  20.50    953,904           8.10               20.14          432,327           20.13
21.00 --  37.88    975,373           9.21               26.73           86,870           25.55
</TABLE>

 
     Employee Stock Purchase Plan: In May 1993, the stockholders adopted the
Company's Employee Stock Purchase Plan (the "Purchase Plan"), which was
subsequently amended. A total of 495,000 shares of common stock are reserved for
issuance. Under the terms of the Purchase Plan, employees can choose to have up
to ten percent of their annual compensation withheld to purchase shares of
common stock. The purchase price of the common stock is at 85 percent of the
lower of the fair market value of the common stock at the enrollment or purchase
date. During 1995, 1996 and 1997, 63,000 shares, 160,000 shares and 122,000
shares, respectively, were issued under the Purchase Plan.
 
     Pro Forma Information: The Company has retained the approach under APB
Opinion No. 25 and related interpretations in accounting for its stock option
and purchase plans. Accordingly, no compensation expense has been recognized for
its Option Plan, Directors Plan and Purchase Plan. Had compensation expense for
the Company's stock option and purchase plans been determined consistent with
Statement No. 123, the Company's net loss per share applicable to common stock
would have been increased to the pro forma amounts indicated below (table in
thousands, except per share amounts):
 

<TABLE>
<CAPTION>
                                                                1995        1996        1997
                                                                ----        ----        ----
<S>                                            <C>            <C>         <C>         <C>
Net loss applicable to common stock..........  As reported    $(17,292)   $ (5,651)   $(15,538)
                                               Pro forma       (17,608)    (10,152)    (23,746)
Net loss per common share....................  As reported    $  (1.18)   $  (0.34)   $  (0.83)
                                               Pro forma         (1.20)      (0.61)      (1.27)
</TABLE>

 
     Pro forma net loss applicable to common stock reflects only stock option
and purchase rights granted in 1995, 1996 and 1997. Therefore, the full impact
of calculating compensation expense for stock options and stock purchase rights
under Statement No. 123 is not reflected in the pro forma net loss amounts
presented above since compensation expense is reflected over the stock option
vesting and stock purchase subscription periods and compensation expense for
stock options and stock purchase rights granted prior to January 1, 1995 are not
considered. The fair value of each option grant is estimated on the date of
grant using the Black-Scholes option-pricing model with the following
weighted-average assumptions used for grants in 1997, 1996 and 1995: dividend
yield of zero percent; expected volatility of 61.4 percent; risk-free interest
rate of 6.3 percent; and an expected option life of 5.7 years for 1997; and a
dividend yield of zero percent; expected volatility of 66.8 percent; risk-free
interest rate of 6.2 percent; and an expected option life of 5.5 years for 1996
and 1995. The per share weighted-average fair value of stock options granted
during 1995, 1996 and 1997 at an exercise price equal to the fair market value
on the date of grant was $2.42, $13.25 and $16.09, respectively, on the date of
grant using the Black-Scholes option-pricing model. The fair value of each
purchase right is
 
                                       50

<PAGE>   53
                IDEC PHARMACEUTICALS CORPORATION AND SUBSIDIARY
 
             NOTES TO CONSOLIDATED FINANCIAL STATEMENTS (CONTINUED)
 
estimated on the date of enrollment using the Black-Scholes option-pricing model
with the following assumptions used in 1997, 1996 and 1995: dividend yield of
zero percent; expected volatility of 61.4 percent; risk-free interest rates
between 5.5 percent and 6.0 percent; and an expected life between 0.3 year and
2.0 years for 1997; and a dividend yield of zero percent; expected volatility of
66.8 percent; risk-free interest rates between 5.6 percent and 5.9 percent; and
an expected life between 0.3 year and 2.0 years for 1996 and 1995. The per share
weighted-average fair value of stock purchase rights granted during 1995, 1996
and 1997 was $2.65, $9.05 and $10.50, respectively, on the subscription date
using the Black-Scholes option-pricing model.
 
     Stock Warrants: Under an investment agreement and in part subject to the
Company's accomplishments of certain research and development objectives, SR One
Limited, SmithKline Beecham's venture capital subsidiary, purchased 200,000
common stock warrants in each 1993 and 1992. In October 1996, these warrants
were exercised for 400,000 shares of the Company's common stock resulting in net
proceeds of $4,755,000.
 
     In December 1994 and August 1995, concurrent with the completion of a debt
financing, the Company issued warrants for the purchase of 294,000 shares and
46,000 shares, respectively, of common stock. The holders of the warrants have
the option to exchange their warrants, without the payment of cash or
consideration, for a number of common shares equal to the difference between the
number of shares resulting by dividing the aggregate exercise price of the
warrants by the fair market value of the common stock on the date of exercise
and the number of shares that would have been otherwise issued under the
exercise. In 1996 and 1997, 196,000 warrants and 114,000 warrants, respectively,
were exchanged for 169,000 shares and 105,000 shares, respectively, of the
Company's common stock. At December 31, 1997, 30,000 warrants to purchase common
stock were outstanding. Such warrants have a six-year term and are immediately
exercisable at $6.22 per share.
 
NOTE 9: INCOME TAXES
 
     The following table summarizes the tax effects of temporary differences
that give rise to significant portions of the deferred tax assets and
liabilities at December 31, 1996 and 1997 (table in thousands):
 

<TABLE>
<CAPTION>
                                                                1996        1997
                                                              --------    --------
<S>                                                           <C>         <C>
Deferred tax assets:
  Accrued expenses..........................................  $    531    $    609
  Property and equipment, principally due to difference in
     depreciation...........................................       448       1,194
  Deferred rent expense.....................................       607         803
  Amortization of fair value change in common stock
     warrants...............................................       776         770
  Deferred revenue..........................................        --       2,372
  Capitalized state research and experimentation costs......     2,090       2,189
  Acquired technology rights................................     4,336       3,695
  Research and experimentation credit.......................     5,078       6,070
  Net operating loss carryforwards..........................    24,247      29,601
  Other tax assets..........................................       333         696
                                                              --------    --------
          Total gross deferred tax assets...................    38,446      47,999
Valuation allowance.........................................   (38,446)    (47,737)
Deferred tax liabilities....................................        --        (262)
                                                              --------    --------
Net deferred taxes..........................................  $     --    $     --
                                                              ========    ========
</TABLE>

 
     In 1995, 1996 and 1997, the Company recognized an increase in the valuation
allowance of $7,652,000, $3,882,000 and $9,291,000, respectively.
 
                                       51

<PAGE>   54
                IDEC PHARMACEUTICALS CORPORATION AND SUBSIDIARY
 
             NOTES TO CONSOLIDATED FINANCIAL STATEMENTS (CONTINUED)
 
     As of December 31, 1997, the Company had net operating loss and research
and experimentation tax credit carryforwards for Federal income tax purposes of
approximately $82,000,000 and $4,000,000, respectively, which expire beginning
in 1999. Net operating loss carryforwards and research and experimentation tax
credit carryforwards as of December 31, 1997 for state income tax purposes are
approximately $21,000,000 and $2,000,000, respectively, which expire beginning
in 1998 and 1999, respectively.
 
     The utilization of net operating losses and tax credits incurred prior to
the Company's initial public offering in 1991, may be subject to an annual
limitation under the Internal Revenue Code, due to a cumulative change in
ownership of more than fifty percent. However, the Company believes that such
limitations will not have a material impact upon the utilization of such net
operating loss carryforwards.
 
NOTE 10: COMMITMENTS
 
     Lease Commitments: In July 1992, the Company entered into a 15-year
operating lease for its headquarters, which commenced in 1993. The Company has
the option to extend the term of the lease for two additional periods of five
years each. In August 1996, the Company entered into a 7-year lease for
additional office and warehouse facilities. The Company has the option to extend
the term of this lease for two additional years. In addition to the monthly
lease payments, both lease agreements provide for the Company to pay all
operating expenses associated with the facilities. The lease agreements provide
for scheduled rental increases; accordingly lease expense is recognized on a
straight-line basis over the term of the leases.
 
     Future minimum lease payments under all operating leases as of December 31,
1997, are as follows (table in thousands):
 

<TABLE>
<S>                                                          <C>
1998.......................................................  $ 3,158
1999.......................................................    3,422
2000.......................................................    3,559
2001.......................................................    3,702
2002.......................................................    3,850
2003 and thereafter........................................   18,445
                                                             -------
          Total minimum lease payments.....................  $36,136
                                                             =======
</TABLE>

 
     Lease expense under all operating leases totaled $3,097,000, $3,011,000 and
$3,677,000 for the years ended December 31, 1995, 1996 and 1997, respectively.
 
   
     License Agreements: In September 1997, the Company and Cytokine Networks,
Inc. ("CNI") entered into a development and license agreement for the
development of inflammatory and autoimmune disease products based upon CNI's
anti-MIF antibody technology. Concurrent with the development and license
agreement the Company and CNI entered into a stock purchase agreement providing
for certain equity investments in CNI by the Company. Under the terms of these
agreements, the Company may make payments totaling up to $10,500,000, subject to
the attainment of certain product development milestone events. Additionally,
the Company will pay CNI royalties on sales by the Company of any products
emerging from the collaboration. In 1997, the Company made a $3,000,000
preferred equity investment in CNI.
    
 
   
     In February 1997, the Company acquired exclusive rights from Pharmacia &
Upjohn S.p.A. ("Pharmacia") to 9-aminocamptothecin ("9-AC"), a broad spectrum,
anti-cancer agent for the treatment of cancer. Under the terms of the asset
transfer agreement, the Company may make payments totaling up to $16,000,000,
subject to the attainment of certain product development milestone events. No
royalties are payable to Pharmacia on sales by the Company of any commercialized
products emerging from the agreement. In 1997, the Company made an up-front
licensing payment of $3,000,000 to Pharmacia. The Company anticipates achieving
a product development milestone event in 1999 that would result in the Company
making a $6,000,000 payment to Pharmacia.
    
 
                                       52

<PAGE>   55
                IDEC PHARMACEUTICALS CORPORATION AND SUBSIDIARY
 
             NOTES TO CONSOLIDATED FINANCIAL STATEMENTS (CONTINUED)
 
     In connection with its research and development efforts, the Company has
entered into various license agreements which provide the Company with rights to
develop, produce and market products using certain know-how, technology and
patent rights maintained by the parties. Terms of the various license agreements
require the Company to pay royalties from future sales, if any, on specified
products using the resulting technology. Third party royalty liabilities
resulting from sales of Rituxan are being paid by Genentech and recorded under
the joint business arrangement as described under "Revenues from Unconsolidated
Joint Business" in Notes 1 and 7. As of December 31, 1997, such other royalties,
other than annual minimum royalties payments, have not commenced on the
aforementioned license agreements.
 
                                       53

<PAGE>   56
 
                IDEC PHARMACEUTICALS CORPORATION AND SUBSIDIARY
 

                          INDEPENDENT AUDITORS' REPORT
 
The Board of Directors and Stockholders
IDEC Pharmaceuticals Corporation:
 
     We have audited the accompanying consolidated balance sheets of IDEC
Pharmaceuticals Corporation and subsidiary as of December 31, 1996 and 1997, and
the related consolidated statements of operations, stockholders' equity, and
cash flows for each of the years in the three-year period ended December 31,
1997. These consolidated financial statements are the responsibility of the
Company's management. Our responsibility is to express an opinion on these
consolidated financial statements based on our audits.
 
     We conducted our audits in accordance with generally accepted auditing
standards. Those standards require that we plan and perform the audit to obtain
reasonable assurance about whether the financial statements are free of material
misstatement. An audit includes examining, on a test basis, evidence supporting
the amounts and disclosures in the financial statements. An audit also includes
assessing the accounting principles used and significant estimates made by
management, as well as evaluating the overall financial statement presentation.
We believe that our audits provide a reasonable basis for our opinion.
 
     In our opinion, the consolidated financial statements referred to above
present fairly, in all material respects, the financial position of IDEC
Pharmaceuticals Corporation and subsidiary as of December 31, 1996 and 1997, and
the results of their operations and their cash flows for each of the years in
the three-year period ended December 31, 1997, in conformity with generally
accepted accounting principles.
 
                                                           KPMG Peat Marwick LLP
San Diego, California
February 6, 1998

 
                                       54

<PAGE>   57
 

I
TEM 9. CHANGES IN AND DISAGREEMENTS WITH ACCOUNTANTS ON ACCOUNTING AND
FINANCIAL DISCLOSURE.
 
     None.
 

                                    PART III
 

ITEM 10. DIRECTORS AND EXECUTIVE OFFICERS OF THE REGISTRANT.
 
     Certain information about the Company's executive officers and directors as
of January 31, 1998 is set forth below:
 
   

<TABLE>
<CAPTION>
                 NAME                    AGE                       TITLE
                 ----                    ---                       -----
<S>                                      <C>    <C>
William H. Rastetter, Ph.D.............  49     President, Chief Executive Officer and
                                                Chairman of the Board of Directors
Christopher J. Burman..................  48     Senior Vice President, Manufacturing and
                                                Process Sciences
Antonio J. Grillo-Lopez, M.D...........  58     Senior Vice President, Medical and
                                                Regulatory Affairs
Nabil Hanna, Ph.D......................  54     Senior Vice President, Research and
                                                Preclinical Development
William R. Rohn........................  54     Senior Vice President, Commercial Operations
John Geigert, Ph.D.....................  48     Vice President, Quality
Connie L. Matsui.......................  44     Vice President, Planning and Resource
                                                Development
Phillip M. Schneider...................  41     Vice President and Chief Financial Officer
Kenneth J. Woolcott....................  39     Vice President, Secretary, General Counsel
                                                and Licensing Executive
Charles C. Edwards, M.D................  74     Director
Alan Burnett Glassberg.................  61     Director
John Groom.............................  59     Director
Kazuhiro Hashimoto.....................  57     Director
Franklin P. Johnson, Jr................  69     Director
Robert W. Pangia.......................  46     Director
Bruce R. Ross..........................  56     Director
The Honorable Lynn Schenk..............  53     Director
William D. Young.......................  53     Director
</TABLE>

    
 
     DR. RASTETTER was appointed Chairman of the Board of Directors of the
Company on May 22, 1996. He has served as President and Chief Executive Officer
of the Company since December 1986 and Chief Financial Officer from 1988 to
1993. Dr. Rastetter has served as a Director of the Company since 1986. From
1984 to 1986, he was Director of Corporate Ventures at Genentech. From 1982 to
1984, Dr. Rastetter served in a scientific capacity at Genentech, directing the
Biocatalysis and Chemical Sciences groups. From 1975 to 1982, he held various
faculty positions at the Massachusetts Institute of Technology. Dr. Rastetter
received his Ph.D. in chemistry from Harvard University in 1975.
 
   
     MR. BURMAN joined the Company in May 1992 as Vice President, Manufacturing
Sciences and has served as Senior Vice President, Manufacturing and Process
Sciences since December 1997. He previously served from 1989 to 1992 as Director
of Manufacturing Technology at Life Sciences International. From 1985 to 1989,
he was t-PA Operations and Technical Services Manager at Genentech, where he was
responsible for the start-up of the t-PA manufacturing facility and
commercial-scale manufacturing operations. From 1967 to 1985, he held a series
of positions at Wellcome Biotech Ltd., culminating in responsibility for
worldwide cell culture manufacturing operations. Mr. Burman holds a B.Sc. with
honors in Applied Biology from the Council for National Academic Awards in the
United Kingdom. He also holds graduate qualifications in Industrial
Microbiology.
    
 
                                       55

<PAGE>   58
 
     DR. GRILLO-LOPEZ joined the Company as Vice President, Medical and
Regulatory Affairs in November 1992 from Du Pont Merck Pharmaceutical Company
("Du Pont Merck"). In January 1996, he was promoted to Senior Vice President,
Medical and Regulatory Affairs. He was employed by Du Pont Merck from 1987 to
1992, where he most recently was Executive Medical Director for International
Clinical Research and Development and previously held various clinical and
medical director positions at Du Pont Merck. From 1980 to 1987, Dr. Grillo-Lopez
was a Vice President in charge of clinical therapeutics and Director of Clinical
Oncology Research at Warner Lambert Company's Parke Davis Pharmaceutical
Research Division. He trained as a hematologist and oncologist at the University
of Puerto Rico School of Medicine, San Juan, where he received his M.D. and
subsequently held faculty appointments. He has been an adjunct associate
professor in the Department of Medicine (Hematology and Medical Oncology) at the
University of Michigan Medical School, was a founder of the Puerto Rico Society
of Hematology and the Latin American Society of Hematology, and is a fellow of
the International Society of Hematology and the Royal Society of Medicine
(London).
 
   
     DR. HANNA joined the Company in February 1990 as Vice President, Research
and Preclinical Development. In 1993, Dr. Hanna was promoted to Senior Vice
President, Research and Preclinical Development. From 1981 to 1990, Dr. Hanna
served as Associate Director and then Director of the Department of Immunology
at SmithKline Beecham focusing on autoimmune and chronic inflammatory diseases.
From 1978 to 1981, he was a research scientist at the NCI-Frederick Cancer
Research Center, where he studied the role of immune system cells in host
defenses against cancer. From 1973 to 1978, Dr. Hanna was a lecturer in the
Department of Immunology at the Hebrew University Medical School in Israel,
where he received his Ph.D. in Immunology. Pursuant to the Company's agreement
with CNI, Dr. Hanna is a director of CNI.
    
 
     MR. ROHN joined the Company in August 1993 as Senior Vice President,
Commercial and Corporate Development. Prior to joining the Company, Mr. Rohn was
employed by Adria Laboratories ("Adria"), from 1984 until August 1993, most
recently as Senior Vice President of Sales and Marketing with responsibilities
for strategic and commercial partnerships as well as all sales and marketing
functions in the United States. Prior to Adria, Mr. Rohn held marketing and
sales management positions at Abbott Laboratories, Warren-Teed Pharmaceuticals,
Miles Laboratories and Mead Johnson Laboratories. Mr. Rohn received a B.A. in
Marketing from Michigan State University.
 
   
     DR. GEIGERT joined the Company in May 1996 as Vice President, Quality. He
previously served from 1991 to May 1996 as Vice President, Quality Control at
Immunex Corporation, a biotechnology company. From 1973 to 1991, he was employed
by Cetus Corporation where he served most recently as Director of Quality
Control and Product Evaluation. Dr. Geigert holds a B.S. degree in Chemistry
from Washington State University and a Ph.D. in Organic Chemistry/Analytical
Chemistry from Colorado State University.
    
 
     MS. MATSUI joined the Company in November 1992 as Senior Director, Planning
and Resource Development with primary responsibility for strategic planning and
human resources. In December 1994, Ms. Matsui was promoted to Vice President,
Planning and Resource Development. Ms. Matsui's current responsibilities include
investor relations, corporate communications, human resources, project
management and strategic planning. As a consultant during 1992, Ms. Matsui
assisted in the planning and implementation of the Company's unification from
sites in Northern and Southern California to its present site in San Diego. From
1977 to 1991, she served in a variety of marketing and general management
positions at Wells Fargo Bank including Vice President and Manager responsible
for Consumer Retirement Programs and Vice President and Manager in charge of
company-wide Employee Relations and Communications. Ms. Matsui received her B.A.
and M.B.A. from Stanford University.
 
     MR. SCHNEIDER joined the Company in February 1987 as Director, Finance and
Administration and served as Senior Director, Finance and Administration from
1990 to 1991. In 1991, he became Vice President, Finance and Administration and
in 1996 he was appointed Vice President and Chief Financial Officer. From 1984
to 1987, Mr. Schneider served as the Manager of Financial Reporting and as a
Senior Analyst for Syntex Laboratories. He received a B.S. in biochemistry from
University of California, Davis, received his M.B.A. at
 
                                       56

<PAGE>   59
 
the University of Southern California and earned his C.P.A. qualifications while
working for KPMG Peat Marwick LLP as a Senior Accountant.
 
   
     MR. WOOLCOTT joined the Company in March 1989 as Intellectual Property
Counsel. In 1990, he became Intellectual Property and Licensing Counsel. Mr.
Woolcott was promoted to Deputy General Counsel in 1991 and General Counsel in
1992. In 1993, Mr. Woolcott was appointed Secretary of the Company. In 1994, he
was promoted to Vice President, Secretary, General Counsel & Licensing
Executive. From 1985 to 1987, he served as Patent Counsel and Associate Counsel
at Hybritech, Inc. From 1987 to 1989, he was engaged in the private practice of
law in Seattle, Washington. Mr. Woolcott received a B.S. in Biochemistry from
Pacific Lutheran University and his J.D. from George Washington University.
    
 
   
     DR. EDWARDS is the retired President and Chief Executive Officer of Scripps
Institution of Medicine and Science (the "Institute"). Dr. Edwards joined the
Institution in 1991 and retired in 1994. Dr. Edwards served as the President and
Chief Executive Officer of Scripps Clinic and Research Foundation from 1977 to
1991. Previously, Dr. Edwards held a number of positions with private, public
and governmental entities including Commissioner of the FDA and several
positions with the American Medical Association. Dr. Edwards is director of
three other publicly traded companies, Bergen Brunswig Corporation, Molecular
Biosystems, Inc., Northern Trust of California and various privately held
companies. He received his B.S., M.D. and Honorary Degree, Doctor of Science
from the University of Colorado and received his M.S. in Surgery from the
University of Minnesota. Dr. Edwards has served as a Director of the Company
since May 1995.
    
 
     DR. GLASSBERG is Associate Director of Clinical Care and Director of
General Oncology at the University of California San Francisco Cancer Center,
and also serves as Director of Hematology and Medical Oncology at Mount Zion
Medical Center in San Francisco, California. Dr. Glassberg has been associated
with the University of California, San Francisco since 1970 and is currently a
Clinical Professor of Medicine. He received his M.D. from the Medical University
of South Carolina in Charleston. Dr. Glassberg has served as a Director of the
Company since February 1997.
 
     MR. GROOM has been President, Chief Executive Officer, and a Director of
Elan Corporation plc, a public company registered in Ireland, since July 1996.
Mr. Groom served as the President and Chief Executive Officer of Athena
Neurosciences, Inc., a biotechnology company ("Athena"), from 1987 to June 1996
prior to Athena's acquisition by Elan Corporation. From 1960 to 1985, Mr. Groom
was employed by Smith Kline & French Laboratories ("SK&F"), the pharmaceutical
division of the former SmithKline Beckman Corporation. He held a number of
positions at SK&F, including: President of SK&F International from 1980 to 1985.
Mr. Groom has served as Chairman of the International Section of the
Pharmaceutical Manufacturers Association. He serves as a Director of Ligand
Pharmaceuticals Incorporated and as a public trustee to the Research Foundation
of the American Academy of Neurology. Mr. Groom is a Fellow of the Association
of Certified Accountants (U.K.) and has served as a Director of the Company
since September 1992.
 
   
     MR. HASHIMOTO has been, since 1981, Director of Research and Development of
Zenyaku, a private pharmaceutical company in Tokyo, Japan, and an investor in
the Company. Mr. Hashimoto was promoted to President of Zenyaku in July 1994. He
has served on Zenyaku's board of directors since 1977, is a director of various
privately held companies and sits on the Board of Trustees of Tamagawa Gakuen
University. Mr. Hashimoto received his B.A. in Commerce from Tamagawa Gakuen
University and his B.A. in Business Administration from Lewis & Clark College.
Mr. Hashimoto has served as a Director of the Company since July 1991.
    
 
   
     MR. JOHNSON has been, since 1967, the general partner of Asset Management
Partners, an investor in the Company. Mr. Johnson is also Chairman of the Board
of Boole and Babbage, Inc., and a director of Amgen, Inc. and various privately
held companies. Mr. Johnson received his B.S. in Mechanical Engineering from
Stanford University and received his M.B.A. from Harvard University. Mr. Johnson
has served as a Director of the Company since 1986.
    
 
     MR. PANGIA has worked in investment banking for 20 years and is currently
self-employed in that capacity. Most recently, he served as Executive Vice
President and Director of Investment Banking for PaineWebber Incorporated of New
York ("PaineWebber"). He held other various senior management
 
                                       57

<PAGE>   60
 
   
positions at PaineWebber including member of the board of directors of
PaineWebber, Inc., Chairman of the board of directors of PaineWebber Properties,
Inc., member of PaineWebber's executive and operating committees, chairman of
the equity commitment committee and member of the debt commitment committee.
Prior to his positions at PaineWebber, Mr. Pangia held other senior positions
including Managing Director in Investment Banking for Drexel Burnham Lambert of
New York and Vice President of Investment Banking for Kidder, Peabody & Co. of
New York. Mr. Pangia is a director of two other publicly traded companies, IWS
Corporation and Ryan, Beck & Co. He received his A.B. from Brown University and
his M.B.A. from Columbia University. Mr. Pangia has served as a Director of the
Company since September 1997.
    
 
     MR. ROSS is currently President of Cancer Rx, a health care consulting
firm. Immediately prior to launching Cancer Rx, Mr. Ross was Chief Executive
Officer of the National Comprehensive Cancer Network, an association of fifteen
of the largest cancer centers in the United States. He previously held senior
management positions, during a 27-year career, at Bristol-Myers Squibb,
including Senior Vice President, Policy, Planning and Development, Bristol-Myers
Squibb Pharmaceutical Group and President, Bristol-Myers Squibb U.S.
Pharmaceutical Group. Mr. Ross currently serves as a director for Fox Chase
Cancer Center and Sugen, Inc. He received his B.S. from Syracuse University and
later was a Bristol-Myers Scholar at the Yale School of Organization and
Management. Mr. Ross has served as a Director of the Company since July 1997.
 
     MS. SCHENK is currently an attorney in private practice and previously
served as the U.S. Congresswoman for the 49th District of the State of
California from 1993 to 1995. She worked as an attorney in private practice from
1983 to 1993 and served as the California Secretary of Business, Transportation
and Housing from 1980 to 1983. Ms. Schenk is also a director of Cal Fed Bank.
She received her B.A. in Political Science from the University of California at
Los Angeles, earned her J.D. from the University of San Diego and attended the
London School of Economics. Ms. Schenk has served as a Director of the Company
since May 1995.
 
     MR. YOUNG is currently Chief Operating Officer of Genentech. Mr. Young
joined Genentech in 1980 as Director of Manufacturing and Process Sciences and
became Vice President in 1983. He was promoted to Senior Vice President in 1989
where he was responsible for Process Sciences, Manufacturing, Engineering,
Quality, Regulatory Affairs, Product Development and Pharmacological Sciences.
In 1986, Mr. Young was promoted to Executive Vice President. He became Chief
Operating Officer in 1997, taking on the additional responsibilities Medical
Affairs and Business Development and Sales and Marketing. Prior to joining
Genentech, Mr. Young was with Eli Lilly & Co., where he held several positions
in pharmaceutical engineering, antibiotic process development and manufacturing
management. Mr. Young holds a B.S. in Chemical Engineering from Purdue
University and an M.B.A. from Indiana University. He was elected to the National
Academy of Engineering in 1993 for his contributions to biotechnology. Mr. Young
is also a director of Energy Biosystems, Inc. Mr. Young has served as a Director
of the Company since May 1997.
 
     The information required by Section 16(a) is hereby incorporated by
reference to the information contained under the caption "Compliance with
Section 16(a) of the Securities Exchange Act of 1934" in the Company's Proxy
Statement for its Annual Meeting of Stockholders to be held on May 21, 1998.
 

ITEM 11. EXECUTIVE COMPENSATION.
 
     The information required by this item is hereby incorporated by reference
to the information contained under the caption "Executive Compensation and
Related Information" in the Company's Proxy Statement for its Annual Meeting of
Stockholders to be held on May 21, 1998.
 
                                       58

<PAGE>   61
 

ITEM 12. SECURITY OWNERSHIP OF CERTAIN BENEFICIAL OWNERS AND MANAGEMENT.
 
     The following table sets forth certain information known to the Company
with respect to the beneficial ownership of the Company's Common Stock as of
January 31, 1998, by (i) all persons who are beneficial owners of five percent
or more of the Company's Common Stock, (ii) each director; (iii) certain
executive officers and (iv) all current directors and executive officers of the
Company as a group.
 
   

<TABLE>
<CAPTION>
                                                                 SHARES         PERCENTAGE
                                                              BENEFICIALLY     BENEFICIALLY
            NAME AND ADDRESS OF BENEFICIAL OWNER                 OWNED           OWNED(1)
            ------------------------------------              ------------     ------------
<S>                                                           <C>              <C>
Oracle Partners, L.P........................................   1,647,700            8.4%
  712 Fifth Avenue, 45 Floor
  New York, New York 10019
Genentech, Inc. (2).........................................   1,490,793            7.1%
  One DNA Way
  South San Francisco, California 94080
American Century Investment Management, Inc.................   1,418,800            7.2%
  4500 Main Street, 15th Floor
  Kansas City, MO 64111
Dean Witter InterCapital Inc. (3)...........................   1,048,000            5.3%
  Two World Trade Center, 71st Floor
  New York, NY 10048
Charles C. Edwards, M.D. (4)................................      33,500              *
John Geigert, Ph.D.(5)......................................      28,224              *
Alan B. Glassberg, M.D. (6).................................      22,500              *
Antonio J. Grillo-Lopez, M.D. (7)...........................     171,946              *
John Groom (8)..............................................      42,500              *
Nabil Hanna, Ph.D. (9)......................................     293,507            1.5%
Kazuhiro Hashimoto (10).....................................     691,667            3.5%
Franklin P. Johnson, Jr. (11)...............................      81,737              *
Robert W. Pangia (12).......................................      18,500              *
William H. Rastetter, Ph.D. (13)............................     513,371            2.6%
William R. Rohn (14)........................................     173,491              *
Bruce R. Ross (15)..........................................      17,500              *
The Honorable Lynn Schenk (16)..............................      34,500              *
William D. Young (17).......................................   1,490,793            7.1%
All directors and executive officers as a group (18 persons)
  (3 through 18)............................................   4,177,141           18.3%
</TABLE>

    
 
- ---------------
 
  *  Less than 1%.
 
   
 (1) Percentage of beneficial ownership is calculated assuming 19,630,694 shares
     of Common Stock were outstanding on January 31, 1998. Beneficial ownership
     is determined in accordance with the rules of the Commission and generally
     includes voting or investment power with respect to securities. Shares of
     Common Stock subject to options and warrants currently exercisable or
     exercisable within sixty days after January 31, 1998, as well as Nonvoting
     Convertible Preferred Stock, are deemed outstanding for computing the
     percentage of the person holding such options but are not deemed
     outstanding for computing the percentage of any other person. Except as
     indicated by footnote, and subject to community property laws where
     applicable, the persons named in the table have sole voting and investment
     power with respect to all shares of Common Stock shown as beneficially
     owned by them.
    
 
   
 (2) Includes Nonvoting Convertible Preferred Stock convertible into 1,490,793
     shares held by Genentech. Mr. Young, a director of the Company, disclaims
     beneficial ownership of the Nonvoting Convertible Preferred Stock held by
     Genentech.
    
 
                                       59

<PAGE>   62
 
 (3) Dean Witter InterCapital Inc. is a wholly-owned subsidiary of Morgan
     Stanley, Dean Witter, Discover & Co., an affiliate of one of the
     Underwriters of this offering.
 
 (4) Includes options to purchase 32,500 shares held by Dr. Edwards.
 
 (5) Includes options to purchase 27,968 shares held by Dr. Geigert.
 
 (6) Includes options to purchase 22,500 shares held by Dr. Glassberg.
 
 (7) Includes options to purchase 161,998 shares held by Dr. Grillo-Lopez.
 
 (8) Includes options to purchase 42,500 shares held by Mr. Groom.
 
 (9) Includes options to purchase 281,095 shares held by Dr. Hanna.
 
(10) Includes 666,667 shares held by Zenyaku. Mr. Hashimoto, a director of the
     Company, disclaims beneficial ownership of such shares. Includes options to
     purchase 25,000 shares held by Mr. Hashimoto.
 
(11) Includes 34,303 shares beneficially owned by Asset Management Partners. Mr.
     Johnson, a director of the Company, is the General Partner of Asset
     Management Partners. Mr. Johnson disclaims beneficial ownership of such
     shares except to the extent of his pecuniary interest arising from his
     interest in Asset Management Partners. Includes options to purchase 25,000
     shares held by Mr. Johnson.
 
(12) Includes options to purchase 18,500 shares held by Mr. Pangia.
 
(13) Includes options to purchase 415,719 shares held by Dr. Rastetter.
 
(14) Includes options to purchase 146,266 shares held by Mr. Rohn.
 
(15) Includes options to purchase 17,500 shares held by Mr. Ross.
 
(16) Includes options to purchase 32,500 shares held by Ms. Schenk.
 
(17) Includes Nonvoting Convertible Preferred Stock convertible into
     approximately 1,490,793 shares held by Genentech. Mr. Young, a director of
     the Company, disclaims beneficial ownership of the Nonvoting Convertible
     Stock held by Genentech.
 
(18) Includes options to purchase 1,699,280 shares and Nonvoting Convertible
     Preferred Stock convertible into 1,490,793 shares of Common Stock.
 

ITEM 13. CERTAIN RELATIONSHIPS AND RELATED TRANSACTIONS.
 
     The information required by this item is hereby incorporated by reference
to the information contained under the caption "Certain Relationships and
Related Transactions" in the Company's Proxy Statement for its Annual Meeting of
Stockholders to be held on May 21, 1998.
 
                                       60

<PAGE>   63
 

                                    PART IV
 

ITEM 14. EXHIBITS, FINANCIAL STATEMENT SCHEDULES AND REPORTS ON FORM 8-K.
 
a. (1) Consolidated Financial Statements:
 

<TABLE>
<CAPTION>
                                                                     PAGE
                                                                     ----
       <S>                                                           <C>
       Consolidated Balance Sheets -- December 31, 1996 and 1997...   *
       Consolidated Statements of Operations -- Years ended
         December 31, 1995, 1996 and 1997..........................   *
       Consolidated Statements of Stockholders' Equity -- Years
         ended December 31, 1995, 1996 and 1997....................   *
       Consolidated Statements of Cash Flows--Years ended December
         31, 1995, 1996 and 1997...................................   *
       Notes to Consolidated Financial Statements..................   *
       Independent Auditors' Report................................   *
</TABLE>

 
       * These items are in Item 8 to this Form 10-K.
 
   (2) Financial Statement Schedules:
 

<TABLE>
<CAPTION>
       SCHEDULE NUMBER                            DESCRIPTION
       ---------------                            -----------
       <C>                <S>
             II           Valuation and qualifying accounts
</TABLE>

 
            All other financial statements schedules are omitted because they
       are not required or are not applicable, or because the required
       information is included in the financial statements or notes thereto.
 
   (3) Exhibits:
 

<TABLE>
<CAPTION>
        EXHIBIT
         NUMBER                              DESCRIPTION
        -------                              -----------
       <S>           <C>
       2.1(1)        Agreement and Plan of Merger dated as of April 5, 1997
                     between the Registrant and IDEC California.
       3.1(1)        Amended and Restated Articles of Incorporation of the
                     Registrant.
       3.2(1)        Bylaws of the Registrant.
       4.1           Reference is made to Exhibit 3.1.
       4.2           Reference is made to Exhibit 3.2.
       4.3(2)        1992 Amended and Restated Registration Rights Agreement of
                     IDEC California.
       4.4(1)        Specimen Common Stock Certificate of the Registrant.
       4.5           Reference is made to Exhibit 10.46
       4.6(7)        1995 Registration Rights Agreement of the Registrant.
       4.7(17)       Agreement Regarding Registration Rights and Related
                     Obligations pursuant to the ISDA Master Agreement between
                     the Registrant and Swiss Bank Corporation. London Branch.
       4.8(18)       Preferred Share Purchase Rights
       10.1(13)      1988 Stock Option Plan of the Registrant, as amended and
                     restated through May 22, 1997.
       10.2(13)      Form of Notice of Grant.
       10.3(13)      Form of Option Agreement.
       10.4(12)      Letter Agreement between the Registrant and Genentech, Inc.,
                     dated May 21, 1996
       10.5(2)       401(k) Plan of the Registrant.
       10.6(2)       Form of acceleration of vesting letter agreement between the
                     Registrant and certain officers.
</TABLE>

 
                                       61

<PAGE>   64
 

<TABLE>
<CAPTION>
        EXHIBIT
         NUMBER                              DESCRIPTION
        -------                              -----------
       <S>           <C>
       10.7(2)+      License Agreement with Coulter Immunology, dated May 16,
                     1991.
       10.8(3)       Lease Agreement between the Registrant and Torrey Sorrento,
                     Inc., dated July 9, 1992.
       10.9(3)+      Collaborative Research and License Agreement between the
                     Registrant and SmithKline Beecham p.l.c., dated October 12,
                     1992.
       10.10(3)      Investment Agreement between the Registrant and S.R. One,
                     Limited, dated October 16, 1992.
       10.11(13)     1995 Employee Stock Purchase Plan, as amended and restated
                     through May 22, 1997.
       10.12(4)+     Collaborative Development Agreement between the Registrant
                     and Mitsubishi Chemical Corporation, dated November 11,
                     1993.
       10.13(4)      Employment Agreement between the Registrant and Dr. Antonio
                     Grillo-Lopez dated September 25, 1992.
       10.14(5)      1993 Non-Employee Directors Stock Option Plan.
       10.15(6)+     Collaborative Development Agreement between the Registrant
                     and Seikagaku Corporation dated December 27, 1994.
       10.16(6)+     License Agreement between the Registrant and Seikagaku
                     Corporation dated December 27, 1994.
       10.17(6)+     Loan Agreement between the Registrant and Silicon Valley
                     Bank and Venture Lending & Leasing, Inc., dated December 28,
                     1994.
       10.18(6)+     $2,500,000 Promissory Note, dated December 28, 1994.
       10.19(6)+     $5,000,000 Promissory Note, dated December 28, 1994.
       10.20(6)      Security Agreement, dated December 28, 1994.
       10.21(6)+     Patent Collateral Assignment, dated December 28, 1994.
       10.22(6)+     Trademark Collateral Assignment, dated December 28, 1994.
       10.23(6)      Intercreditor Agreement, dated December 28, 1994.
       10.24(6)      Deed of Trust and Fixture Filing, dated December 28, 1994.
       10.25(6)      Three-Party Leasehold Agreement, dated September 30, 1994.
       10.26(6)      Warrants to Purchase Shares of Common Stock, dated December
                     30, 1994.
       10.27(6)      1994 Registration Rights Agreement.
       10.28(6)      Investment Agreement between the Registrant, SmithKline
                     Beecham p.1.c. and SmithKline Beecham Corporation, dated
                     December 28, 1994.
       10.29(7)      Master Definitions Agreement between the Registrant and
                     Genentech. Inc.
       10.30(7)+     Collaboration Agreement between the Registrant and
                     Genentech. Inc., dated March 16, 1995.
       10.31(7)+     Expression Technology Agreement between the Registrant and
                     Genentech. Inc., dated March 16, 1995.
       10.32(7)      Preferred Stock Purchase Agreement between the Registrant
                     and Genentech. Inc., dated March 16, 1995.
       10.33(7)      Option Agreement between the Registrant and Genentech, Inc.,
                     dated March 16, 1995.
       10.34(7)      Preferred and Common Stock Purchase Agreement between the
                     Registrant and ML/MS Associates, L.P., dated March 16, 1995.
</TABLE>

 
                                       62

<PAGE>   65
 

<TABLE>
<CAPTION>
        EXHIBIT
         NUMBER                              DESCRIPTION
        -------                              -----------
       <S>           <C>
       10.35(9)*     Amendment Agreement between the Registrant and SmithKline
                     Beecham p.1.c., dated January 20, 1993.
       10.36(9)*     Modification of the Amendment Agreement between the
                     Registrant and SmithKline Beecham p.1.c., dated June 14,
                     1993.
       10.37(8)      Special Stock Issuance Plan.
       10.38(10)     $2,500,000 Promissory Note, dated August 11, 1995.
       10.39(10)     Warrants to purchase shares of common stock, dated August 9,
                     1995.
       10.40(15)+    Collaborative Development Agreement between the Registrant
                     and Eisai Co., Ltd. dated p.1.c., dated June 14, 1993.
       10.41(15)+    License Agreement between the Registrant and Eisai Co., Ltd.
                     dated December 11, 1995.
       10.42(15)+    License Agreement between the Registrant, Genentech, Inc.
                     and Zenyaku Kogyo Co., Ltd. dated p.1.c., dated June 14,
                     1993.
       10.43(15)+    Development Agreement between the Registrant, Genentech,
                     Inc. and Zenyaku Kogyo Co., Ltd. dated November 30, 1995.
       10.44(15)+    Supply Agreement between the Registrant and Zenyaku Kogyo
                     Co., Ltd. dated November 30, 1995.
       10.45(15)+    Termination Agreement between the Registrant and Zenyaku
                     Kogyo Co., Ltd. dated November 30, 1995.
       10.46(15)+    Amendment to the Development Agreement between the
                     Registrant, Genentech, Inc. and Zenyaku Kogyo Co., Ltd.
                     dated November 30, 1995.
       10.47(15)     Amendment to Collaboration Agreement between the Registrant
                     and Genentech, Inc. dated November 30, 1995.
       10.48(11)+    License Agreement between the Registrant and Chugai
                     Pharmaceutical Co., Ltd., dated March 31, 1996.
       10.49(14)     Lease Agreement between the Registrant and All Spectrum
                     Services, Inc., dated August 13, 1996.
       10.50(1)      Form of Indemnification Agreement for Officers and
                     Directors.
       10.51(16)+    9-AC Asset Transfer Agreement between the Registrant,
                     Pharmacia & Upjohn S.p.A. and Pharmacia & Upjohn Company,
                     dated February 10, 1997.
       10.52(17)     ISDA Master Agreement between the Registrant and Swiss Bank
                     Corporation, London Branch, dated August 26, 1997, together
                     with Schedules thereto.
       10.53(17)+    Confirmation for Contract A entered into pursuant to the
                     ISDA Master Agreement between the Registrant and Swiss Bank
                     Corporation, London Branch.
       10.54(17)+    Confirmation for Contract B entered into pursuant to the
                     ISDA Master Agreement between the Registrant and Swiss Bank
                     Corporation, London Branch.
       22.1(2)       Subsidiary of the Company.
       23.0          Independent Auditors' Report on Schedule and Consent
       23.1          Financial Statement Schedule
       27.1          Financial Data Schedule
</TABLE>

 
- ---------------
 
   * Confidential Treatment requested as to certain portions of this agreement.
 
  + Confidential Treatment has been granted with respect to portions of this
    agreement.
 
                                       63

<PAGE>   66
 
 (1) Incorporated by reference to exhibit filed with the Registrant's
     Registration Statement on Form 8-B filed on June 2, 1997.
 
 (2) Incorporated by reference to exhibit filed with the Registrant's
     Registration Statement on Form S-1, File No. 33-40756.
 
 (3) Incorporated by reference to exhibit filed with the Registrant's Annual
     Report on Form 10-K for the year ended December 31, 1992.
 
 (4) Incorporated by reference to exhibit filed with the Registrant's
     Registration Statement on Form S-1, File No. 33-76080.
 
 (5) Incorporated by reference to exhibit filed with the Registrant's
     Registration Statement on Form S-8, File No. 33-93794.
 
 (6) Incorporated by reference to exhibit filed with the Registrant's Annual
     Report on Form 10-K for the year ended December 31, 1994.
 
 (7) Incorporated by reference to exhibit filed with the Registrant's Quarterly
     Report on Form 10-Q for the quarter ended March 31, 1995.
 
 (8) Incorporated by reference to exhibit filed with the Registrant's
     Registration Statement on Form S-8, File No. 33-90738.
 
 (9) Incorporated by reference to exhibit filed with the Registrant's Quarterly
     Report on Form 10-Q for the quarter ended June 30, 1995.
 
(10) Incorporated by reference to exhibit filed with the Registrant's Quarterly
     Report on Form 10-Q for the quarter ended September 30, 1995.
 
(11) Incorporated by reference to exhibit filed with the Registrant's Quarterly
     Report on Form 10-Q for the quarter ended March 31, 1996.
 
(12) Incorporated by reference to exhibit filed with the Registrant's
     Registration Statement on Form 8-K, dated May 21, 1996.
 
(13) Incorporated by reference to exhibit filed with the Registrant's
     Registration Statement on Form S-8, File No. 333-2969.
 
(14) Incorporated by reference to exhibit filed with the Registrant's Quarterly
     Report on Form 10-Q for the quarter ended September 30, 1996.
 
(15) Incorporated by reference to exhibit filed with the Registrant's Annual
     Report on Form 10-K for the year ended December 31, 1995.
 
(16) Incorporated by reference to exhibit filed with the Registrant's Quarterly
     Report on Form 10-Q for the quarter ended June 30, 1997.
 
(17) Incorporated by reference to exhibit filed with the Registrant's Quarterly
     Report on Form 10-Q for the quarter ended September 30, 1997.
 
(18) Incorporated by reference to exhibit filed with the Registrant's
     Registration Statement on Form 8-A, dated August 1, 1997.
 
     b. No reports on Form 8-K were filed during the fourth quarter of 1997.
 
                                       64

<PAGE>   67
 

                                   SIGNATURES
 
     Pursuant to the requirements of Section 13 or 15(d) of the Securities
Exchange Act of 1934, the Registrant has duly caused this report to be signed on
its behalf by the undersigned, thereunto duly authorized.
 
                                          IDEC PHARMACEUTICALS CORPORATION
 
   
Date: March 2, 1998                       By:   /s/ WILLIAM H. RASTETTER
    
                                            ------------------------------------
                                                William H. Rastetter, Ph.D.
                                               Chairman, President and Chief
                                                      Executive Officer
 
   
     KNOW ALL MEN BY THESE PRESENTS, that each person whose signature appears
below constitutes and appoints jointly and severally, William H. Rastetter and
Phillip M. Schneider, or either of them as his or her true and lawful
attorneys-in-fact and agents, with full power of substitution and
resubstitution, for him or her and in his or her name, place and stead, in any
and all capacities, to sign any and all amendments to this Report on Form 10-K,
and to file the same, with all exhibits thereto, and other documents in
connection therewith, with the Securities and Exchange Commission, granting unto
said attorneys-in-fact and agents, and each of them, full power and authority to
do and perform each and every act and thing requisite and necessary to be done
in connection therewith, as fully to all intents and purposes as he might or
could do in person, hereby ratifying and confirming all that said
attorneys-in-fact and agents, or any of them, or their or his substitute or
substitutes, may lawfully do or cause to be done by virtue hereof.
    
 
   
     IN WITNESS WHEREOF, each of the undersigned has executed this Power of
Attorney as of the date indicated.
    
 
     Pursuant to the requirements of the Securities Exchange Act of 1934, this
report has been signed by the following persons on behalf of the Registrant and
in the capacities and on the dates indicated.
 
   

<TABLE>
<CAPTION>
                        NAME                                       CAPACITY                    DATE
                        ----                                       --------                    ----
<S>                                                      <C>                             <C>
 
              /s/ WILLIAM H. RASTETTER                     Chairman, President and           March 2, 1998
- -----------------------------------------------------      Chief Executive Officer
             William H. Rastetter, Ph.D.                     (Principal Executive
                                                                   Officer)
 
              /s/ PHILLIP M. SCHNEIDER                        Vice President and             March 2, 1998
- -----------------------------------------------------      Chief Financial Officer
                Phillip M. Schneider                       (Principal Financial and
                                                             Accounting Officer)
 
               /s/ CHARLES C. EDWARDS                              Director                  March 2, 1998
- -----------------------------------------------------
              Charles C. Edwards, M.D.
 
                                                                   Director                  March _, 1998
- -----------------------------------------------------
               Alan B. Glassberg, M.D.
 
                   /s/ JOHN GROOM                                  Director                  March 2, 1998
- -----------------------------------------------------
                     John Groom
 
               /s/ KAZUHIRO HASHIMOTO                              Director                  March 2, 1998
- -----------------------------------------------------
                 Kazuhiro Hashimoto
 
                                                                   Director                  March _, 1998
- -----------------------------------------------------
              Franklin P. Johnson, Jr.
</TABLE>

    
 
                                       65

<PAGE>   68
 
   

<TABLE>
<CAPTION>
                        NAME                                       CAPACITY                    DATE
                        ----                                       --------                    ----
<S>                                                      <C>                             <C>
                /s/ ROBERT W. PANGIA                               Director                  March 2, 1998
- -----------------------------------------------------
                  Robert W. Pangia
 
                                                                   Director                  March _, 1998
- -----------------------------------------------------
                    Bruce R. Ross
 
            /s/ THE HONORABLE LYNN SCHENK                          Director                  March 2, 1998
- -----------------------------------------------------
              The Honorable Lynn Schenk
 
                                                                   Director                  March _, 1998
- -----------------------------------------------------
                  William D. Young
</TABLE>

    
 
                                       66





<PAGE>   1
                                                                    EXHIBIT 23.0

                 IDEC PHARMACEUTICALS CORPORATION AND SUBSIDIARY


              INDEPENDENT AUDITORS' REPORT ON SCHEDULE AND CONSENT





The Board of Directors
IDEC Pharmaceuticals Corporation:

The audits referred to in our report dated February 6, 1998, included the
related financial statement schedule as of December 31, 1997, and for each of
the years in the three-year period ended December 31, 1997, included in the 1997
Annual Report on Form 10-K. This financial statement schedule is the
responsibility of the Company's management. Our responsibility is to express an
opinion on this financial statement schedule based on our audits. In our
opinion, such financial statement schedule, when considered in relation to the
basic consolidated financial statements taken as a whole, presents fairly in all
material respects the information set forth therein.

We consent to incorporation by reference in registration statements Nos.
333-2969 and 33-93794 on Forms S-8 of IDEC Pharmaceuticals Corporation of our
report dated February 6, 1998, relating to the consolidated balance sheets of
IDEC Pharmaceuticals Corporation and subsidiary as of December 31, 1996 and
1997, and the related consolidated statements of operations,
 shareholders'
equity and cash flows for each of the years in the three-year period ended
December 31, 1997, which report appears in the 1997 Annual Report on Form 10-K
of IDEC Pharmaceuticals Corporation. We also consent to the use of our report on
the related schedule included herein, and to the reference to our firm under
the heading "Selected Financial Data" in the Form 10-K.



                                          KPMG PEAT MARWICK LLP



San Diego, California
February 27, 1998





<PAGE>   1

                                                                    EXHIBIT 23.1

                                   SCHEDULE II

                 IDEC PHARMACEUTICALS CORPORATION AND SUBSIDIARY

                        VALUATION AND QUALIFYING ACCOUNTS
                                 (In thousands)

                  Years Ended December 31, 1995, 1996 and 1997



<TABLE>
<CAPTION>
                                                                   Additions
                                                            -----------------------
                                                 Balance    Charged to   Charged to                   Balance
                                                beginning   costs and      other                      at End
Description                                      of year     expenses     accounts     Deductions     of Year
- -----------                                     ---------   ----------   ----------    ----------     -------
<S>                                              <C>             <C>      <C>           <C>           <C>    
Year ended December 31, 1995
    Allowance for contract revenue
       receivables                               $   --       $   --      $   658       $    --       $   658
                                                 ------      -------      -------       -------       -------
                                                 $   --       $   --      $   658       $    --       $   658
                                                 ======      =======      =======       =======       =======

Year ended December 31, 1996
    Allowance for contract revenue
       receivables                               $  658      $    --      $ 1,423       $  (400)      $ 1,681
                                                 ------      -------      -------       -------       -------
                                                 $  658      $    --      $ 1,423       $  (400)      $ 1,681
                                                 ======      =======      =======       =======       =======

Year ended December 31, 1997
    Inventory reserve                            $   --      $ 2,082      $    --       $    --       $ 2,082
    Allowance for contract revenue
       receivables                                1,681           --           --        (1,630)           51
                                                 ------      -------      -------       -------       -------
                                                 $1,681      $ 2,082      $    --       $(1,630)      $ 2,133
                                                 ======      =======      =======       =======       =======
</TABLE>






<TABLE> <S> <C>

<ARTICLE> 5
<LEGEND>
THIS SCHEDULE CONTAINS SUMMARY FINANCIAL INFORMATION EXTRACTED FROM THE
CONSOLIDATED BALANCE SHEETS AND CONSOLIDATED STATEMENTS OF OPERATIONS CONTAINED
IN EXHIBIT 13.3 OF THE COMPANY'S ANNUAL REPORT ON FORM 10-K FOR THE YEAR ENDED
DECEMBER 31, 1997 AND IS QUALIFIED IN ITS ENTIRETY BY REFERENCE TO SUCH
FINANCIALS STATEMENTS AND THE NOTES THERETO.
</LEGEND>
<MULTIPLIER> 1,000
       
<S>                             <C>
<PERIOD-TYPE>                   12-MOS
<FISCAL-YEAR-END>                          DEC-31-1997
<PERIOD-START>                             JAN-01-1997
<PERIOD-END>                               DEC-31-1997
<CASH>                                          34,847
<SECURITIES>                                    34,810
<RECEIVABLES>                                    3,971
<ALLOWANCES>                                         0
<INVENTORY>                                      4,134
<CURRENT-ASSETS>                                79,193
<PP&E>                                          35,933
<DEPRECIATION>                                  12,484
<TOTAL-ASSETS>                                 106,013
<CURRENT-LIABILITIES>                           19,432
<BONDS>                                              0
<PREFERRED-MANDATORY>                                0
<PREFERRED>                                          0
<COMMON>                                            19
<OTHER-SE>                                      80,660
<TOTAL-LIABILITY-AND-EQUITY>                   106,013
<SALES>                                              0
<TOTAL-REVENUES>                                44,606
<CGS>                                                0
<TOTAL-COSTS>                                   51,282
<OTHER-EXPENSES>                                     0
<LOSS-PROVISION>                                     0
<INTEREST-EXPENSE>                                 917
<INCOME-PRETAX>                                      0
<INCOME-TAX>                                         0
<INCOME-CONTINUING>                                  0
<DISCONTINUED>                                       0
<EXTRAORDINARY>                                      0
<CHANGES>                                            0
<NET-INCOME>                                  (15,538)
<EPS-PRIMARY>                                   (0.83)
<EPS-DILUTED>                                        0
        

</TABLE>