BIOGEN’S AVONEX® (Interferon beta-1a) APPROVED IN EUROPE FOR TREATMENT OF PATIENTS AT HIGH RISK FOR DEVELOPING MULTIPLE SCLEROSIS

Only MS Drug in Europe to Carry this Approved Indication of Use

Biogen, Inc. (NASDAQ/BGEN) today announced that the EMEA, the European Regulatory Agency for pharmaceuticals, has approved AVONEX for use in the treatment of patients who are at high risk of developing Clinically Definite Multiple Sclerosis (CDMS). In countries throughout Europe, AVONEX can now be prescribed after a patient has one multiple sclerosis (MS) attack and when alternative diagnoses have been excluded.

The standard practice of MS diagnosis and treatment has previously been only after patients have experienced two separate and distinct attacks or demyelinating events. This decision by the EMEA makes AVONEX the only MS treatment approved for earlier use, after the first attack, when patients are considered at high risk for developing MS.

The approval is based on data submitted to the EMEA from Biogen’s long-term clinical study known as CHAMPS (Controlled High Risk Subjects AVONEX Multiple Sclerosis Prevention Study). The study, published in the New England Journal of Medicine (NEJM), was also cited by The Harvard Health Letter as one of the top ten medical advances in the year 2000. Results from CHAMPS, to be presented at the European Neurology Society (ENS) meeting in June, showed a 66% reduction in the risk of developing CDMS based on clinical measures and MRI scans of the brain in a high-risk subgroup of patients.

The EMEA decision means that the indication extension is valid in all 15 member states of the European Union (EU) as well as Norway and Ireland. In addition to Europe, Biogen has received approval in Australia for earlier use, after the first attack, based on the CHAMPS data. This indication is not approved in the United States; an application is pending with the FDA.

Commenting on the European approval, Hans Peter Hasler, Biogen’s Executive Vice President, Commercial Operations said, “The European decision on AVONEX is a testament to Biogen’s clinical programs and to the product itself. Biogen has maintained a commitment to people with MS through rigorous scientific research, enriched patient programs and first-class customer support.”

About AVONEX® (Interferon-beta 1a)

AVONEX is the leading treatment for relapsing forms of multiple sclerosis worldwide, with more than 121,000 patients on therapy. It was launched in the U.S. in 1996 and is marketed in more than 65 countries for the treatment of relapsing forms of MS to slow the progression of disability and reduce relapses.

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.

About Biogen

Biogen, Inc., winner of the U.S. National Medal of Technology, is a biotechnology 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 worldwide sales of AVONEX for treatment of relapsing forms of multiple sclerosis, and from the sales by licensees of a number of products. (Please see full prescribing information at http://www.avonex.com.) 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.