Biogen Idec Announces Multiple Sclerosis Franchise and Pipeline Presentations at the European Committee for Treatment and Research of Multiple Sclerosis

Biogen Idec (NASDAQ: BIIB) today announced that nearly 25 posters
and symposia sponsored by the company will be presented at the 23rd
Congress of the European Committee for Treatment and Research of
Multiple Sclerosis (ECTRIMS) in Prague, Czech Republic. These
presentations and symposia will cover five agents that are marketed or
currently in development by Biogen Idec and its partners for the
treatment of multiple sclerosis (MS). The two approved therapies for
MS are TYSABRI(R)(natalizumab) and AVONEX(R) (Interferon beta-1a); and
agents in development are BG-12 (dimethyl fumarate), daclizumab and
RITUXAN(R) (rituximab).

"The number of presentations and symposia by Biogen Idec at
ECTRIMS are evidence of our dedication and leadership in discovering
and developing treatments for multiple sclerosis patients," said
Alfred Sandrock, MD, PhD, Senior Vice President, Neurology Research
and Development, Biogen Idec. "Biogen Idec strives to provide a
continuum of care for all MS patients at every stage of their disease.
Building upon the foundation that we established with TYSABRI and
AVONEX, our extensive clinical pipeline looks to the future. In
addition, our compounds in earlier stages of development target such
unmet needs as neurodegeneration and remyelination, with the goal to
reverse the damage inflicted by MS."

The following are selected highlights of presentations at ECTRIMS:

TYSABRI

-- Use of natalizumab in patients with relapsing multiple
sclerosis: updated safety results from TOUCH(TM) and TYGRIS
(Poster #565 - Saturday, October 13, 2007, 3:30 p.m. CEST)

-- Natalizumab increases the proportion of patients with multiple
sclerosis who are disease-free (Poster #567 - Saturday,
October 13, 2007, 3:30 p.m. CEST)

-- The effect of plasma exchange in accelerating clearance of
natalizumab in patients with multiple sclerosis: results of
the PLEX study (Poster #576 - Saturday, October 13, 2007, 3:30
p.m. CEST)

AVONEX

-- Progression of disability at two years predicts disability at
eight years: analysis from the Phase III clinical trial of
intramuscular Interferon beta-1a (Poster #195 - Friday,
October 12, 2007, 3:30 p.m. CEST)

-- Final results from the Global QUASIMS Study: a worldwide
comparative study of the efficacy and tolerability of
interferon-beta products for the treatment of relapsing
multiple sclerosis (Poster #197 - Friday, October 12, 2007,
3:30 p.m. CEST)

BG-12

-- Two Phase III studies to determine the efficacy and safety of
BG-12, a novel, oral fumaric acid derivative, in patients with
relapsing multiple sclerosis (Poster #579 - Saturday, October
13, 2007, 3:30 p.m. CEST)

-- Activation of Nrf2 and modulation of disease progression in
EAE models by BG-12 (dimethyl fumarate) suggests a novel
mechanism of action combining anti-inflammatory and
neuroprotective modalities (Poster #503 - Friday, October 12,
2007, 3:30 p.m. CEST)

"We are excited about BG-12's novel, dual mechanism of action,"
continued Dr. Sandrock. "With approval to run the Phase III studies in
17 countries, we are pleased to have a global program that offers both
anti-inflammatory and neuroprotective properties to patients in need."

Daclizumab

Daclizumab is a humanized monoclonal antibody to the IL-2 receptor
of T cells that is in Phase II development for MS.

-- Preliminary CHOICE results: a Phase II, randomised,
double-blind, placebo-controlled multicentre study of
subcutaneous daclizumab in patients with active, relapsing
forms of multiple sclerosis on interferon beta (Platform
Presentation #50 - Friday, October 12, 2007, 2:50 p.m. CEST)

RITUXAN

RITUXAN is a targeted B-cell therapy that is in development for
MS.

-- Safety and efficacy of rituximab in adults with
relapsing-remitting multiple sclerosis: results of a Phase II
placebo-controlled, multicentre trial through 48 weeks (Poster
#554 - Saturday, October 13, 2007, 3:30 p.m. CEST)

Biogen Idec and Elan Corporation, plc will also be hosting two
symposia during ECTRIMS: "Optimising MS therapy to fit patients'
lives" will be held on Thursday, October 11, 2007 at 2:30 p.m. CEST
and "Urgency to treat: can we modify the course of MS?" will be held
on Friday, October 12, 2007 at 6:00 p.m. CEST. Both symposia will be
held in the Main Hall of the Prague Congress Centre.

About Biogen Idec

Biogen Idec creates new standards of care in therapeutic areas
with high unmet medical needs. Founded in 1978, Biogen Idec is a
global leader in the discovery, development, manufacturing, and
commercialization of innovative therapies. Patients in more than 90
countries benefit from Biogen Idec's significant products that address
diseases such as lymphoma, multiple sclerosis, and rheumatoid
arthritis. For product labeling, press releases and additional
information about the company, please visit www.biogenidec.com.

About Our Products

TYSABRI

TYSABRI is a treatment approved for relapsing forms of MS in the
United States and relapsing-remitting MS in the European Union.
According to data that have been published in the New England Journal
of Medicine, after two years, TYSABRI treatment led to a 68% relative
reduction (p<0.001) in the annualized relapse rate compared to placebo
and reduced the relative risk of disability progression by 42-54%
(p<0.001).

TYSABRI increases the risk of progressive multifocal
leukoencephalopathy (PML), an opportunistic viral infection of the
brain that usually leads to death or severe disability. Other serious
adverse events that have occurred in TYSABRI-treated patients included
hypersensitivity reactions (e.g., anaphylaxis) and infections. Serious
opportunistic and other atypical infections have been observed in
TYSABRI-treated patients, some of whom were receiving concurrent
immunosuppressants. Herpes infections were slightly more common in
patients treated with TYSABRI. In MS trials, the incidence and rate of
other serious and common adverse events, including the overall
incidence and rate of infections, were balanced between treatment
groups. Common adverse events reported in TYSABRI-treated patients
include headache, fatigue, infusion reactions, urinary tract
infections, joint and limb pain, and rash.

In addition to the United States and European Union, TYSABRI is
also approved in Switzerland, Canada, Australia, New Zealand and
Israel. TYSABRI was discovered by Elan and is co-developed with Biogen
Idec.

AVONEX

AVONEX is the most prescribed treatment for relapsing forms of MS
worldwide, with more than 130,000 patients on therapy. It is used
worldwide as a treatment for relapsing forms of MS to slow the
progression of disability and reduce relapses. AVONEX is also approved
for patients who have their first clinical MS attack and have a brain
MRI scan consistent with MS. The most common side effects associated
with AVONEX multiple sclerosis treatment are flu-like symptoms,
including myalgia, fever, fatigue, headache, chills, nausea, vomiting,
pain and asthenia.

AVONEX should be used with caution in patients with depression or
other mood disorders and in patients with seizure disorders. AVONEX
should not be used by pregnant women. Patients with cardiac disease
should be closely monitored. Patients should also be monitored for
signs of hepatic injury.

Daclizumab

Although daclizumab is currently marketed for other uses, it is
not approved for use in patients with multiple sclerosis.

RITUXAN

Although RITUXAN is currently marketed for other uses, it is not
approved for use in patients with multiple sclerosis.

For full prescribing information on TYSABRI and warnings that come
with the product, please visit www.tysabri.com. For full prescribing
information on AVONEX, please visit www.avonex.com. For full
prescribing information on RITUXAN, please visit www.rituxan.com.

Safe Harbor/Forward-Looking Statements

This press release contains forward-looking statements about our
expected product sales, product development and other matters.
Forward-looking statements are subject to risks and uncertainties that
could cause actual results to differ materially from that which we
expect. The commercial potential of products in pre-clinical and
clinical development is subject to a number of risks and
uncertainties, including the risk of unexpected delays or hurdles and
the uncertainty of obtaining regulatory approval. Drug development and
commercialization involves a high degree of risk. Additional factors
that could cause our actual results to differ include our continued
dependence on our two principal products, AVONEX and RITUXAN, the
uncertainty of success in commercializing other products including
TYSABRI, the occurrence of adverse safety events with our products,
the failure to execute our growth strategy successfully or to compete
effectively in our markets, our dependence on collaborations over
which we may not always have full control, possible adverse impact of
government regulation and changes in the availability of reimbursement
for our products, problems with our manufacturing processes and our
reliance on third parties, fluctuations in our operating results, our
ability to protect our intellectual property rights and the cost of
doing so, the risks of doing business internationally and the other
risks and uncertainties that are described in Item 1A "Risk Factors"
in our most recent Form 10-Q filing with the SEC. These
forward-looking statements speak only as of the date of this press
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