AVONEX(R), The #1 Prescribed Multiple Sclerosis Therapy Worldwide, Improves Patient Convenience.

Additional Supplemental Application for Room Temperature Storage with Prefilled Syringe Approved by FDA 

CAMBRIDGE, Mass. -- AVONEX([R]) (Interferon beta-1a), the most prescribed multiple sclerosis (MS) therapy worldwide, may now be stored at room temperature (up to 77F or 25C) in its prefilled formulation for a period up to 7 days.

"As someone who is constantly on the go, being able to store my AVONEX at room temperature for up to 7 days is very convenient." said Cathy F. who has been taking AVONEX for 9 years.

AVONEX remains the only once-a-week disease modifying therapy to both slow the progression of physical disability and reduce the frequency of clinical relapses for people with MS.

"Biogen Idec is committed to the discovery and development of new therapeutic options for people living with MS as well as continuous improvement of existing ones ." said Michael Panzara MD, MPH, VP, Chief Medical Officer, Neurology Strategic Business Unit.

About AVONEX

AVONEX is the most prescribed treatment for relapsing forms of multiple sclerosis worldwide, with more than 130,000 patients on therapy. It was launched in the U.S. in 1996 and later in Europe for the treatment of relapsing forms of MS to slow the progression of physical disability and reduce relapses in patients with relapsing forms of MS. AVONEX demonstrated a 37% reduction in the risk of progression of physical disability over two years compared with placebo. In addition, AVONEX has been shown to reduce the risk of developing a second relapse by 44% for up to three years. AVONEX is marketed internationally in more than 90 countries. AVONEX was the first treatment approved for MS patients who have their first clinical MS attack and have a brain MRI scan that suggests MS; this use was approved in Europe in 2002 and in the U.S. in 2003.

The most common side effects associated with AVONEX treatment are flu-like symptoms including myalgia, fever, fatigue, headache, chills, nausea, vomiting, pain and asthenia.

AVONEX should be used in caution with 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. Routine periodic blood chemistry and hematology tests are recommended during treatment with AVONEX. Rare cases of anaphylaxis have been reported. Please see complete prescribing information and medication guide available at www.AVONEX.com.

Safe Harbor/Forward Looking Statements

This press release contains forward-looking statements regarding AVONEX that are subject to a number of risks and uncertainties. These statements are based on the companies' current beliefs and expectation. No forward-looking statement can be guaranteed. 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 or 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 periodic reports of Biogen Idec Inc. 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.