United States
SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

SCHEDULE 13G

Under the Securities Exchange Act of 1934

(Amendment No. 1)*

Name of Issuer - IDEC Pharmaceuticals Corp.

Title or Class of Securities - Common Stock

CUSIP Number - 449370105

Check the following box if a fee is being paid with this
statement [  ].


<PAGE>
Cusip No. 449370105

Page 2 of 8 Pages

1.   Name of  Reporting  Person  (S.S.  or  I.R.S.  Identification  No. of above
     person)

     American Century Companies, Inc. - 43-1325032


2.   Check the appropriate box if a member of a group* - N/A

3.   SEC Use Only

4.   Citizenship or place of organization

     Delaware


5.   Sole voting power

     N/A


6.   Shared voting power

     N/A


7.   Sole dispositive power

     N/A


8.   Shared dispositive power

     N/A


9.   Aggregate amount beneficially owned by each reporting person

     N/A


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

     N/A


12.  Type of reporting person*

     HC


<PAGE>
Cusip No. 449370105

Page 3 of 8 Pages

1.   Name of  Reporting  Person  (S.S.  or  I.R.S.  Identification  No. of above
     person)

     American Century Investment Management, Inc. - 44-0640487


2.   Check the appropriate box if a member of a group* - N/A

3.   SEC Use Only

4.   Citizenship or place of organization

     Delaware


5.   Sole voting power

     N/A


6.   Shared voting power

     N/A


7.   Sole dispositive power

     N/A


8.   Shared dispositive power

     N/A


9.   Aggregate amount beneficially owned by each reporting person

     N/A


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

     N/A


12.  Type of reporting person*

     IA


<PAGE>
Cusip No. 449370105

Page 4 of 8 Pages

1.   Name of  Reporting  Person  (S.S.  or  I.R.S.  Identification  No. of above
     person)

     American Century Mutual Funds, Inc. - 44-6006315


2.   Check the appropriate box if a member of a group* - N/A

3.   SEC Use Only

4.   Citizenship or place of organization

     Maryland


5.   Sole voting power

     N/A


6.   Shared voting power

     N/A


7.   Sole dispositive power

     N/A


8.   Shared dispositive power

     N/A


9.   Aggregate amount beneficially owned by each reporting person

     N/A


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

     N/A


12.  Type of reporting person*

     IV


<PAGE>
Cusip No. 449370105

Page 5 of 8 Pages

1.   Name of  Reporting  Person  (S.S.  or  I.R.S.  Identification  No. of above
     person)

     James E. Stowers, Jr. - 492-38-8397


2.   Check the appropriate box if a member of a group* - N/A

3.   SEC Use Only

4.   Citizenship or place of organization

     United States


5.   Sole voting power

     N/A


6.   Shared voting power

     N/A


7.   Sole dispositive power

     N/A


8.   Shared dispositive power

     N/A


9.   Aggregate amount beneficially owned by each reporting person

     N/A


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

     N/A


12.  Type of reporting person*

     IN


<PAGE>
SCHEDULE 13G


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 PERSONS FILING

     American Century Companies, Inc., on its behalf and on behalf of:

     American Century Investment Management, Inc.
     American Century Mutual Funds, Inc.
     James E. Stowers, Jr.


Item 2(b).   ADDRESS OF PRINCIPAL BUSINESS OFFICE OR, IF NONE, RESIDENCE

     4500 Main Street 
     P.O. Box 418210 
     Kansas City, MO 64141-9210  
     Attn:  David H. Reinmiller


Item 2(c).   CITIZENSHIP

     Delaware


Item 2(d).   TITLE OF CLASS OF SECURITIES

     Common Stock


Item 2(e).     CUSIP NO.

     449370105


Item 3.   IF THIS  STATEMENT  IS FILED  PURSUANT TO RULES  13d-1(b) OR 13d-2(b),
          CHECK WHETHER THE PERSON FILING IS A

     (g)  [ X ]   Parent Holding Company, in accordance with
               Rule 13d-1(b)(ii)(G) (Note:  See Item 7).


Item 4.   OWNERSHIP

     (a)  Aggregate amount beneficially owned:

          N/A

     (b)  Percent of class:

          N/A

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

          (i)  sole power to vote or to direct the vote:

               N/A

          (ii) shared power to vote or to direct the vote:

               N/A

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

               N/A

          (iv) shared power to dispose or to direct the disposition of:

               N/A

Item 5.   OWNERSHIP OF FIVE PERCENT OR LESS OF A CLASS

     If this  statement  is being  filed to report  the fact that as of the date
hereof the reporting  person has ceased to be the beneficial  owner of more than
five percent of the class of securities, check the following [X].


Item 6.   OWNERSHIP OF MORE THAN FIVE PERCENT ON BEHALF OF ANOTHER PERSON

     N/A


Item 7.   IDENTIFICATION AND CLASSIFICATION OF THE SUBSIDIARY WHICH ACQUIRED THE
          SECURITY BEING REPORTED ON BY THE PARENT HOLDING COMPANY

     N/A


Item 8.   IDENTIFICATION AND CLASSIFICATION OF MEMBERS OF THE GROUP

     N/A


Item 9.   NOTICE OF DISSOLUTION OF GROUP

     N/A


Item 10.  CERTIFICATION

     By signing  below I certify  that,  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.



February 10, 1999              AMERICAN CENTURY COMPANIES, INC.
     Date

                               By: /s/David C. Tucker

                                   David C. Tucker
                                   General Counsel

<PAGE>
EXHIBIT A

Rule 13d-1(f)(1)(iii) Agreement


     Each of the  undersigned  hereby  agrees and consents to the  execution and
joint filing on its or his behalf by American  Century  Companies,  Inc. of this
Schedule 13G respecting the beneficial ownership of the securities which are the
subject of this schedule at December 31, 1998.

     Dated this 10th day of February, 1999.

                                American Century Companies, Inc.


                                By: /s/David C. Tucker

                                    David C. Tucker
                                    General Counsel


                                American Century Investment Management, Inc.


                                By: /s/David C. Tucker

                                    David C. Tucker
                                    Senior Vice President
                                    and General Counsel


                                American Century Mutual Funds, Inc.


                                By: /s/David C. Tucker

                                    David C. Tucker
                                    Vice President



                                By: /s/David H. Reinmiller

                                    James E. Stowers, Jr.
                                    By David H. Reinmiller,
                                    Attorney in Fact, pursuant to
                                    Power of Attorney dated 2/3/97
                                    on file with Schedule 13G for
                                    U.S. Robotics, Inc. filed 2/3/97