New Long-Term Data on AVONEX® (Interferon beta-1a)

No Difference Seen Between Two Doses At Four Years

Biogen, Inc. (NASDAQ/BGEN) announced that new four year data from its AVONEX dose comparison study were presented today at the Annual Meeting of the American Academy of Neurology (AAN) in Denver, Colorado. This study was designed to see if doubling the approved 30 mcg weekly dose of AVONEX to 60 mcg weekly would produce additional clinical benefit in patients with relapsing forms of multiple sclerosis (MS).

Commenting on his presentation of the four year data, Dr. Ernst-Wilhelm Radue of the Institute for Diagnostic Radiology in Basel, Switzerland said, “These data add significantly to our understanding of AVONEX in the long term treatment of this life-long chronic disease.”

After four years of treatment, there was no difference between the 30 mcg and 60 mcg treatment groups in the cumulative rate of sustained disability progression on the expanded Disability Status Scale (EDSS), decrease in mean relapse rate from baseline, or percentage of relapse-free patients.

“The results are consistent with the pivotal Phase III study and further support the approved 30 mcg dose,” Dr. Radue said, adding, “Physicians and patients can be assured by this study that, when treating relapsing MS, more AVONEX is not better. The 30-mcg dose administered by intramuscular (IM) injection once a week slows the progression of physical disability and reduces the relapses associated with this disease.”

The results presented by Dr. Radue were from an extension of the three-year European Interferon Beta-1a Dose-Comparison Study. Three-year results were reported at last year’s meeting of the European Neurological Society (ENS). This randomized, double-blind trial included 802 patients with relapsing MS at 38 centers in ten countries in Europe; 491 of these patients elected to continue through a fourth year of the study.

About AVONEX® (Interferon-beta 1a)

The most common side effects associated with AVONEX treatment are flu-like symptoms, muscle ache, fever, and chills. Other common side effects seen, but not statistically different between AVONEX and control groups, were headache, pain and asthenia (weakness). These side effects usually go away within a day after the injection and occur less often as the treatment continues. AVONEX should be used with caution in people with depression and people with seizure disorders. AVONEX should not be used by pregnant women. People with cardiac disease should be closely monitored. Routine periodic blood chemistry and hematology tests are recommended during treatment with AVONEX. Please see complete prescribing information available at www.avonex.com.

AVONEX is the leading treatment for multiple sclerosis worldwide, with more than 118,000 patients on therapy. It was launched in the U.S. in 1996 and later in Europe for the treatment of relapsing forms of MS to slow the progression of disability and reduce relapses. AVONEX is marketed internationally in more than 65 countries.

About Biogen

Biogen, Inc., winner of the U.S. National Medal of Technology, is a biopharmaceutical company principally engaged in discovering and developing drugs for human healthcare through genetic engineering. Headquartered in Cambridge, MA, the Company’s revenues are generated from U.S. and worldwide sales of AVONEX® (Interferon beta-1a) for treatment of relapsing forms of multiple sclerosis, and from the worldwide sales by licensees of a number of products, including alpha interferon and hepatitis B vaccines and diagnostic products. Biogen’s research and development activities are focused on novel products to treat inflammatory and autoimmune diseases, neurological diseases, cancer, fibrosis and congestive heart failure. The Company maintains active clinical research programs in protein therapeutics, small molecules, genomics and gene therapy. For copies of press releases and additional information about the Company, please consult Biogen’s Homepage on the World Wide Web at http://www.biogen.com.