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

SCHEDULE 13G

Under the Securities Exchange Act of 1934

(Amendment No. __)*

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

     1,153,700


6.   Shared voting power

     0


7.   Sole dispositive power

     1,153,700


8.   Shared dispositive power

     0


9.   Aggregate amount beneficially owned by each reporting person

     1,153,700


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

     6.0%


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

     1,153,700


6.   Shared voting power

     0


7.   Sole dispositive power

     1,153,700


8.   Shared dispositive power

     0


9.   Aggregate amount beneficially owned by each reporting person

     1,153,700


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

     6.0%


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

     1,131,200


6.   Shared voting power

     0


7.   Sole dispositive power

     1,131,200


8.   Shared dispositive power

     0


9.   Aggregate amount beneficially owned by each reporting person

     1,131,200


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

     5.9%


12.  Type of reporting person*

     IA


<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

     1,153,700


6.   Shared voting power

     0


7.   Sole dispositive power

     1,153,700


8.   Shared dispositive power

     0


9.   Aggregate amount beneficially owned by each reporting person

     1,153,700


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

     6.0%


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:

          1,153,700

     (b)  Percent of class:

          6.0%

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

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

               1,153,700

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

               0

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

               1,153,700

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

               0

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 [ ].


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

     American  Century  Investment  Management,   Inc.  ("ACIM"),  a  registered
investment adviser and a wholly-owned  subsidiary of American Century Companies,
Inc., manages,  pursuant to management  agreements,  the investments of thirteen
registered investment  companies,  American Century Mutual Funds, Inc., American
Century World Mutual Funds,  Inc.,  American Century Capital  Portfolios,  Inc.,
American Century Variable  Portfolios,  Inc., American Century Premium Reserves,
Inc.,  American  Century  Strategic Asset  Allocations,  Inc.,  American Century
Municipal Trust,  American Century  Quantitative  Equity Funds,  Inc.,  American
Century  International  Bond Funds,  Inc.,  American Century  Investment  Trust,
American Century  Government  Income Trust,  American Century Target  Maturities
Trust, and American Century  California  Tax-Free and Municipal Funds, Inc., and
manages, pursuant to sub-advisory agreements,  the investments of two registered
investment companies, American Skandia Trust and American Skandia Advisor Funds,
Inc.  ACIM also  manages  the assets of  institutional  investor  accounts.  The
securities  that are the  subject of this  report are owned by and held for such
investment companies and separate institutional investor accounts. Any dividends
received from such  securities,  or the proceeds of any sale of such securities,
are for the benefit of, and are held for such investment  companies and separate
institutional investor accounts.

     American  Century  Mutual  Funds,  Inc.  owned more than 5% of the class of
securities which are the subject of this report.

     For further information  regarding the ownership of the securities that are
the subject of this report, see Exhibit A attached hereto.


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

     See attached Exhibits A and B.


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 5, 1998              AMERICAN CENTURY COMPANIES, INC.
     Date

                               By: /s/ William M. Lyons
                                   William M. Lyons
                                   President




<PAGE>
EXHIBIT A

IDENTITY AND ITEM 3 CLASSIFICATION OF A SUBSIDIARY OF PARENT HOLDING COMPANIES

     This  Schedule  13G is being  filed by  American  Century  Companies,  Inc.
("ACC").  American Century Investment  Management,  Inc. ("ACIM"), an investment
advisor registered under Section 203 of the Investment  Advisors Act of 1940, is
a  wholly-owned  subsidiary of ACC. Mr. James E. Stowers,  Jr.,  controls ACC by
virtue of his beneficial ownership of a majority of the voting stock of ACC.

     As a result of its  status as  investment  advisor to  thirteen  investment
companies  registered  under  Section  8 of the  Investment  Company  Act and to
several  institutional  investors,  ACIM is deemed to be the beneficial owner of
more than 5% of the class of securities which are the subject of this report.

     ACC, as a result of its control of ACIM,  and Mr.  Stowers,  as a result of
his control of ACC,  are also  deemed to  beneficially  own all such  securities
deemed to be beneficially owned by ACIM. Mr. Stowers,  ACC and ACIM all disclaim
beneficial ownership of such securities.

     The ownership of one investment  company client of ACIM,  American  Century
Mutual Funds,  Inc.  ("ACMF"),  totalled more than 5% of the class of securities
which are the subject of this report.

     This  Schedule 13G is being filed by ACC on behalf of ACC,  ACIM,  ACMF and
Mr. Stowers.



<PAGE>
EXHIBIT B

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, 1997.

     Dated this 5th day of February, 1998.

                                American Century Companies, Inc.


                                By: /s/ William M. Lyons

                                    William M. Lyons
                                    President


                                American Century Investment Management, Inc.


                                By: /s/ William M. Lyons

                                    William M. Lyons
                                    Executive Vice President


                                American Century Mutual Funds, Inc.


                                By: /s/ Patrick A. Looby

                                    Patrick A. Looby
                                    Vice President



                                    /s/ James E. Stowers, Jr.

                                    James E. Stowers, Jr.
                                    Under Power of Attorney dated 2/3/97
                                    on file with Schedule 13G for
                                    U.S. Robotics, Inc. filed 2/3/97