Biogen Idec to Acquire Fumapharm AG; Consolidates Ownership of Oral Compound BG-12 Being Studied for Multiple Sclerosis

Biogen Idec (NASDAQ: BIIB) and Fumapharm AG, a privately
held pharmaceutical company, today announced that they have signed a
definitive agreement for the acquisition of Fumapharm by Biogen Idec.
Fumapharm AG, founded in Switzerland in 1983, develops
therapeutics derived from fumaric acid esters for patients with high
unmet medical need. The company has two products: FUMADERM(R), a
commercial product available in Germany for the treatment of
psoriasis, and BG-12, a clinical-stage product that has been jointly
developed with Biogen Idec. BG-12, an oral fumarate, is being studied
for the treatment of multiple sclerosis (MS) and psoriasis.
"This acquisition supports our goal of developing innovative
therapeutic options for people living with MS," said James C. Mullen,
Biogen Idec's President and Chief Executive Officer. "We look forward
to continuing the development of BG-12, a promising oral compound in
MS, as well as expanding our European operations by working with
Fumapharm's existing partners to provide FUMADERM to psoriasis
patients in Germany."
On May 30, 2006, Biogen Idec and Fumapharm announced positive
results from a Phase II study designed to evaluate the efficacy and
safety of BG-12 in patients with relapsing-remitting 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.
"Biogen Idec is perfectly positioned to continue the development
of BG-12 because of its global commercial and regulatory experience
and unsurpassed expertise in MS. We are proud of the work that
Fumapharm has accomplished in the last 20 years and are confident that
Biogen Idec will continue our legacy of helping patients," said Dr.
Hans Peter Strebel, Chairman and CEO of Fumapharm.
The transaction, which has been approved by the boards of
directors of both companies and is subject to customary closing
conditions, is expected to close within the next two months. Upon
completion, Biogen Idec will acquire all of the issued and outstanding
shares of the capital stock of Fumapharm and will take over
manufacture and sale of FUMADERM for the treatment of psoriasis in
Germany through Fumapharm's existing network. Financial terms of the
transaction were not disclosed.

About BG-12

In October 2003, Biogen Idec licensed certain exclusive worldwide
rights to develop and market BG-12, oral fumarate derivative with an
immunomodulatory mechanism of action, from Fumapharm. Biogen Idec and
Fumapharm are evaluating BG-12 in a range of diseases, including MS
and psoriasis. In April 2005, the companies announced that the primary
endpoint was met in a Phase III study designed to evaluate the
efficacy and safety of BG-12 in the treatment of moderate to severe
psoriasis.
In the Phase II MS study, the most commonly reported adverse
events were flushing, gastrointestinal disorders, headache, and
nasopharyngitis. Liver enzyme elevations were reported in 2% to 8% of
the active treatment groups, compared to 5% in the placebo group.
Infection rates were balanced.

About Fumapharm AG and FUMADERM

Fumapharm is a privately held pharmaceutical company headquartered
in Lucerne, Switzerland. For more information, please visit
http://www.fumapharm.ch.
FUMADERM, an oral product containing fumaric acid esters, was
approved in Germany in 1994 where it is the leading prescription for
oral systemic treatment of severe psoriasis. Fumedica GmbH distributes
FUMADERM in Germany.

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 product
labeling, press releases and additional information about the company,
please visit www.biogenidec.com.

Biogen Idec Safe Harbor

This press release contains forward-looking statements regarding
the acquisition of Fumapharm, the development of BG-12, and the
availability of FUMADERM. These statements are based on the companies'
current beliefs and expectations. Drug development involves a high
degree of risk. Factors which could cause actual results to differ
materially from the companies' current expectations include the risk
that unexpected concerns may arise from additional data or analysis;
that regulatory authorities may require additional information,
further studies, or may fail to approve the drug; the impact of
competitive products on the company's products, a change in market
acceptance of FUMADERM; and that the company may encounter other
unexpected hurdles. For more detailed information on the risks and
uncertainties associated with Biogen Idec's drug development and other
activities, see the section entitled "Risk Factors" in Biogen Idec's
annual report on form 10-K for the fiscal year ended December 31, 2005
that was filed with the Securities and Exchange Commission, as well as
the other periodic and current reports of Biogen Idec filed with the
Securities and Exchange Commission. Biogen Idec assumes no obligation
to update any forward-looking statements, whether as a result of new
information, future events or otherwise.