Biogen Idec Initiates Phase III Clinical Program of Oral Compound BG-12 for Multiple Sclerosis

Biogen Idec (NASDAQ: BIIB) announced today that it has initiated
the Phase III clinical program of BG-12, an oral fumarate in
development for relapsing-remitting multiple sclerosis (MS).

The DEFINE (determination of the efficacy and safety of oral
fumarate in relapsing-remitting MS) and CONFIRM (comparator and an
oral fumarate in relapsing-remitting MS) studies will include more
than 2,000 total patients in North America, Europe and rest of world.
These studies have been initiated internationally, and Biogen Idec
plans to initiate these studies in the U.S. later this year. DEFINE
and CONFIRM are two-year, randomized, multi-center, double-blind,
placebo-controlled, dose-comparison studies to determine the safety
and efficacy of BG-12 in subjects with relapsing-remitting MS. CONFIRM
will also include a glatiramer acetate (Copaxone(R)) reference
comparator arm.

Endpoints of both studies include evaluating the effect of BG-12
on measurements of clinical relapse, the progression of disability,
and various MRI measures.

"Earlier studies of BG-12 support its potential as an oral therapy
for multiple sclerosis. The extensive Phase III clinical program of
BG-12 will provide greater understanding of its promise in MS," said
DEFINE lead investigator Ralf Gold, MD, Professor and Chair of the
Department of Neurology, St. Josef-Hospital/Ruhr-University Bochum.
"MS is a disease that continues to have an unmet need for safe and
effective oral therapeutic options."

"The development of BG-12 furthers Biogen Idec's commitment to
advancing the treatment of MS. We have a diverse portfolio of
therapeutic candidates and are dedicated to the pursuit of innovative
research that will yield multiple options for people living with this
devastating disease,"said Alfred Sandrock, MD, PhD, Senior Vice
President, Neurology Research and Development, Biogen Idec.

BG-12 Phase II Study Results

Data from a Phase II study designed to evaluate the efficacy and
safety of BG-12 were presented at two European neurological medical
meetings in 2006. The 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 orally for six months.
The patient group treated with 720 mg of BG-12 per day had a 69%
reduction (p<0.001) in the mean number of new 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 (p<0.001) in new
or newly enlarging T2-hyperintense lesions at six months compared to
baseline. Although the study was not powered to achieve statistical
significance for this endpoint, there was a 32% reduction (p=0.272) in
relapse rate compared to placebo at the 720 mg dose. The results of
the 120 mg and 360 mg BG-12-treated groups were not statistically
significant versus placebo on any endpoints.

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. The overall rate of infection was
the same in the total BG-12-and placebo-treated groups, and no
opportunistic infections occurred.

About BG-12

Data suggest that BG-12, an oral fumarate derivative, is an
immunomodulator with a novel mechanism of action with a combination of
cytoprotective and anti-inflammatory properties. Based on available
clinical and scientific information with BG-12 and fumarates, there is
strong technical rationale for development of BG-12 in a number of
T-cell mediated autoimmune and/or inflammatory diseases.

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 http://www.biogenidec.com.

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.