IDEC Pharmaceuticals and Biogen Joint Proxy Statement Cleared by SEC

SAN DIEGO and CAMBRIDGE, Mass., Oct. 6 /PRNewswire-FirstCall/ — IDEC Pharmaceuticals Corporation (Nasdaq: IDPH) and Biogen, Inc. (Nasdaq: BGEN) announced today that IDEC’s registration statement on Form S-4 filed in connection with their proposed merger has been declared effective by the Securities and Exchange Commission (SEC). The registration statement includes a joint proxy statement/prospectus that will be sent to the stockholders of both companies.

The proposed merger remains subject to various closing conditions, including the approval of stockholders of IDEC and Biogen. IDEC has scheduled a stockholder meeting to vote on the proposed merger and other matters, including an increase in the number of authorized shares and to issue IDEC common stock in connection with the proposed merger. This stockholder meeting will be held on November 12, 2003 at the Hilton La Jolla Torrey Pines, 10950 North Torrey Pines Road, La Jolla, CA. Biogen has scheduled a stockholder meeting on November 12, 2003 to vote on the proposed merger, to be held at the Biogen offices located at 15 Cambridge Center, Cambridge, MA.

About IDEC Pharmaceuticals

IDEC is a leader in the discovery, development, and commercialization of targeted immunotherapies for the treatment of cancer and autoimmune diseases. IDEC discovered and developed the first commercially available radioimmunotherapy product (Zevalin(R)) approved in the United States, which is used to treat certain non-Hodgkin’s lymphomas. IDEC also discovered and, with co-promotion partner Genentech, Inc., developed the first monoclonal antibody product (Rituxan(R)) approved in the United States for the treatment of cancer. Rituxan is approved in over 70 countries worldwide and is also used to treat various types of non-Hodgkin’s lymphomas. IDEC is a San Diego-based, integrated biopharmaceutical company with multiple products in clinical stage development and strategic alliances in a variety of research platforms. For press releases and additional information about the company, please visit idecpharm.cdmail.biz.

About Biogen

Biogen is the world’s oldest independent biotechnology company and a leader in biologics research, development and manufacturing. A pioneer in leading edge research in immunology, neurobiology and oncology, Biogen brings novel therapies to improve patients’ lives around the world through its global marketing capabilities. For press releases and additional information about the company, please visit www.biogen.com.

Additional Information and Where to Find It

Stockholders of Biogen and IDEC are urged to read the joint proxy statement/prospectus and any other relevant materials filed by Biogen or IDEC with the SEC because they contain, or will contain, important information about IDEC, Biogen and the proposed transaction. The definitive joint proxy statement/prospectus will be sent to the stockholders of Biogen and IDEC seeking their approval of the proposed transaction. Stockholders may obtain a free copy of the definitive joint proxy statement/prospectus and other documents filed by Biogen or IDEC with the SEC at the SEC’s website at www.sec.gov. A free copy of the definitive joint proxy statement/prospectus may also be obtained from Biogen, Inc., 14 Cambridge Center, Cambridge, MA 02142, Attn. Investor Relations or IDEC Pharmaceuticals Corporation, 3030 Callan Road, San Diego, CA 92121 when it becomes available. In addition, stockholders may access copies of the documents filed with the SEC by Biogen on Biogen’s website at www.biogen.com and stockholders may access copies of the documents filed with the SEC by IDEC on IDEC’s website at idecpharm.cdmail.biz. Stockholders are urged to read the definitive joint proxy statement/prospectus and the other relevant materials relating to the proposed transaction before voting or making any investment decision with respect to the proposed transaction.

Biogen, IDEC and their respective executive officers and directors may be deemed to be participants in the solicitation of proxies from their respective stockholders with respect to the proposed transaction. Information about the executive officers and directors of Biogen and their ownership of Biogen common stock is set forth in the proxy statement for Biogen’s 2003 annual meeting of stockholders, which was filed with the SEC on April 17, 2003. Information about the executive officers and directors of IDEC and their ownership of IDEC common stock is set forth in the proxy statement for IDEC’s 2003 annual meeting of stockholders, which was filed with the SEC on April 11, 2003. Information regarding the interests of the officers and directors of Biogen and IDEC in the proposed transaction is set forth in the definitive joint proxy statement/prospectus.

Contacts:

IDEC Vince Reardon Director, Corporate Communications 858-431-8656 Biogen Media Contact: Investment Community Contact Amy Brockelman Elizabeth Woo Manager, Public Affairs Senior Director, Investor Relations 617-914-6524 617-679-2812 Kekst and Company David Lilly Associate 212-521-4878

SOURCE IDEC Pharmaceuticals Corporation; Biogen, Inc.