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                       SECURITIES AND EXCHANGE COMMISSION
                             Washington, D.C. 20549

                                  Schedule 13G

                    Under the Securities Exchange Act of 1934
                              (Amendment No.: 0 )*



Name of issuer:                             IDEC Pharmaceuticals Corp.


Title of Class of Securities:               Common Stock


CUSIP Number:                               449370105


         Check the following [space] if a fee is being paid with this statement:
n/a . (A fee is not  required  only if the  filing  person:  (1) has a  previous
statement on file  reporting  beneficial  ownership of more than five percent of
the class of  securities  described  in Item 1; and (2) has  filed no  amendment
subsequent  thereto  reporting  beneficial  ownership of five percent or less of
such class.) (See rule 13d-7.)

         *The  remainder  of this cover page shall be filled out for a reporting
person's  initial  filing on this  form with  respect  to the  subject  class of
securities,  and for any subsequent amendment containing information which would
alter the disclosures provided in a prior cover page.

         The information  required in the remainder of this cover page shall not
be deemed to be "filed" for the purpose of Section 18 of the Securities Exchange
Act of 1934 ("Act") or otherwise  subject to the  liabilities of that section of
the Act but shall be subject to all other  provisions of the Act  (however,  see
the Notes).


(Continued on the following page(s))

                                Page 1 of 4 Pages

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                                                                 13G

CUSIP No.:  449370105


1.       NAME OF REPORTING PERSON
         S.S. OR I.R.S. IDENTIFICATION NO. OF ABOVE PERSON

                  Vanguard Specialized Funds-Vanguard Health Care Fund

2.       CHECK THE APPROPRIATE [LINE] IF A MEMBER OF A GROUP

         A.                                              B.          X          

3.       SEC USE ONLY



4.       CITIZENSHIP OF PLACE OF ORGANIZATION

                  DELAWARE

(For  questions  5-8,  report  the number of shares  beneficially  owned by each
reporting person with:)

5.       SOLE VOTING POWER

                  1,043,100

6.       SHARED VOTING POWER

                  -0-

7.       SOLE DISPOSITIVE POWER

                  -0-

8.       SHARED DISPOSITIVE POWER

                  1,043,100

9.       AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

                  1,043,100

10.      CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES

                  N/A

11.      PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW 9

                  5.21

12.      TYPE OF REPORTING PERSON

                  IV
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                       SECURITIES AND EXCHANGE COMMISSION
                             Washington, D.C. 20549
                                   ----------

                                  SCHEDULE 13G
                        Under the Securities Act of 1934
                                   ----------


Check the following [line] if a fee is being paid with this statement    n/a

Item 1(a) - Name of Issuer:

                  IDEC Pharmaceuticals Corp.


Item 1(b) - Address of Issuer's Principal Executive Offices:

                  11011 Torreyana Road, San Diego, CA  92121


Item 2(a) - Name of Person Filing:

                  Vanguard Specialized Funds-Vanguard Health Care Fund


Item 2(b) - Title of Class of Securities:

                  Common Stock


Item 2(e) - CUSIP Number

                  449370105


Item 3 - Type of Filing:

         This statement is being filed pursuant to Rule 13d-1. The person filing
is an investment  company  registered under Section 8 of the Investment  Company
Act.


Item 4 - Ownership:


         (a) Amount Beneficially Owned:

                  1,043,100


         (b) Percent of Class:

                  5.21


                                Page 3 of 4 Pages


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         (c) Number of shares as to which such person has:

              (i)  sole power to vote or direct to vote:      1,043,100

              (ii)  shared power to vote or direct to vote:   -0-

              (iii) sole power to dispose of or to direct the disposition of:
                           -0-

              (iv)  shared power to dispose or to direct the disposition of:
                           1,043,100

Item 5 - Ownership of Five Percent or Less of a Class:

         Not applicable

Item 6 - Ownership of More Than Five Percent on Behalf of Another Person:

         Not applicable

Item 7 - Identification  and Classification of the Subsidiary Which Acquired The
Security Being Reported on by the Parent Holding Company:

         Not applicable

Item 8 - Identification and Classification of Members of Group:

         Not applicable

Item 9 - Notice of Dissolution of Group:

         Not applicable

Item 10 - Certification:

         By  signing  below I  certify  than,  to the best of my  knowledge  and
belief, the securities referred to above were acquired in the ordinary course of
business  and were not acquired for the purpose of and do not have the effect of
changing or  influencing  the control of the issuer of such  securities and were
not acquired in connection  with or as a participant in any  transaction  having
such purpose or effect.

Signature

         After reasonable  inquiry and to the best of my knowledge and belief, I
certify that the information  set forth in this statement is true,  complete and
correct.


Date      2-11-99                           By /s/  Raymond J. Klapinsky       
- ----      -------                           ------  --------------------       
                                              Raymond J. Klapinsky

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