EXHIBIT 5

             OPINION AND CONSENT OF PILLSBURY WINTHROP LLP

                                 July 20, 2001


IDEC Pharmaceuticals Corporation
3030 Callan Road
San Diego, California 92121

Re:  Registration Statement on Form S-8


Ladies and Gentlemen:

         With reference to the Registration Statement on Form S-8 to be filed by
IDEC Pharmaceuticals Corporation, a Delaware corporation (the "COMPANY"), with
the Securities and Exchange Commission under the Securities Act of 1933, as
amended, relating to an additional 5,640,000 shares of the Company's Common
Stock which may be issuable pursuant to the Company's 1988 Stock Option Plan
(Amended and Restated Through January 16, 2001) (the "STOCK PLAN"), it is our
opinion that such shares of the Common Stock of the Company, when issued and
sold in accordance with the Stock Plan, will be duly authorized, legally issued,
fully paid and nonassessable.

         We hereby consent to the filing of this opinion with the Securities and
Exchange Commission as an Exhibit to the Registration Statement.

                                      Very truly yours,


                                      /s/ PILLSBURY WINTHROP LLP