Lausanne, Switzerland – May 30, 2006 – Biogen Idec (NASDAQ: BIIB) and Fumapharm AG announced positive results from a Phase II study designed to evaluate the efficacy and safety of BG-12, an oral fumarate, in patients with relapsing-remitting multiple sclerosis (MS). The study achieved its primary endpoint, demonstrating that treatment with BG-12 led to a statistically significant reduction in the total number of gadolinium-enhancing brain lesions as measured by MRI with six months of treatment versus placebo. These data were presented today at the annual meeting of the European Neurological Society in Lausanne, Switzerland.

“We are encouraged that these Phase II data demonstrate that BG-12 may be a promising oral therapy to treat MS. As part of our ongoing commitment to MS patients, we are working with regulatory authorities to determine the next steps in the development of this program,” said Burt Adelman, MD, executive vice president, Development, Biogen Idec.

This Phase II multi-center, double-blind, placebo-controlled, dose-ranging study enrolled 257 patients at sites in 10 countries in Europe. Patients were randomized to receive placebo or BG-12 at 120 mg, 360 mg, or 720 mg per day for six months. The patient group treated with 720 mg of BG-12 per day had a 69% reduction in the mean number of gadolinium-enhancing lesions versus placebo as measured monthly from weeks 12 to 24 of the study. The 720 mg dose group also had a 48% reduction in newly enlarging T2-hyperintense lesions. BG-12 therapy was also associated with a trend towards reduction in relapse rate. The patient group treated with 720 mg of BG-12 per day had a 32% reduction in relapse rate compared to placebo, however, the study was not designed to achieve statistical significance for this endpoint.

The results of the 120 mg and 360 mg BG-12-treated groups were not statistically significant versus placebo. Patients were followed for an additional six months as part of a dose-blinded safety extension study.

The most common adverse events were flushing, gastrointestinal disorders, headache, and nasopharyngitis. The incidence of liver enzyme elevation greater than or equal to three times the upper limit of normal at any time during the placebo controlled phase of the study was between 2% and 8% in the three active treatment groups, compared with 5% in the placebo group. Improvement in liver enzyme levels was seen after discontinuation of BG-12. Infection rates were found to be balanced between the BG-12-and placebo-treated groups and no opportunistic infections occurred.

About Biogen Idec

Biogen Idec creates new standards of care in oncology, neurology and immunology. As a global leader in the development, manufacturing, and commercialization of novel therapies, Biogen Idec transforms scientific discoveries into advances in human healthcare. For press releases and additional information about the company, please visit www.biogenidec.com .

About Fumapharm AG

Fumapharm has licensed exclusive worldwide rights to develop and market BG-12 to Biogen Idec. Fumapharm is a privately held pharmaceutical company headquartered in Lucerne, Switzerland. For more information, please visit www.fumapharm.ch .

Safe Harbor/Forward-Looking Statements

This press release contains forward-looking statements regarding the development of BG-12 for multiple sclerosis. These statements are based on our current beliefs and expectations. They are subject to the risks inherent in drug development, including the risks that the effects of the product in larger clinical trials may not be as expected or that there may be safety issues or other problems or delays that arise during clinical trials, unexpected technical or manufacturing hurdles, or intellectual property disputes. There is no certainty that the risk/benefit profile of the product will be acceptable to the Company or to regulatory authorities for a particular indication. Drug development involves a high degree of risk. Only a small number of research and development programs result in the commercialization of a product.

Success in early stage clinical trials does not ensure that later stage or larger scale clinical trials will be successful. For more detailed information on the risks and uncertainties associated with these forward looking statements and Biogen Idec’s other activities see the periodic and other reports that Biogen Idec has filed with the SEC. Biogen Idec does not undertake any obligation to publicly update any forward-looking statements.

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