AVONEX(R), The Most Prescribed Multiple Sclerosis Therapy Worldwide, May Now Be Given with Smaller Needle; Additional Supplemental Application for Convenient Needle Locking System and Change In Room Temperature Storage Filed with FDA.

CAMBRIDGE, Mass. -- AVONEX(R) (Interferon beta 1a), the most prescribed multiple sclerosis (MS) therapy worldwide may now be administered with a needle that is 20 percent shorter and thinner than the currently approved needle. People living with MS and taking or considering AVONEX may speak with their healthcare provider to see if the smaller needle is appropriate for them.

"Some of my patients have expressed a strong interest in administering AVONEX with a smaller needle," said Dr. Mitchell Freedman from the Triangle MS Center at Raleigh Neurology Associates who is also an Adjunct Professor of Neurology at the University of North Carolina. "The ability to administer AVONEX via a smaller needle may make the once-a-week injection more patient friendly."

Additionally, a supplemental application has been filed with the U.S. Food and Drug Administration (FDA) to provide a new needle attachment, which will lock onto the syringe to make it easier for patients to know that the needle is firmly attached as well as a proposed change in the room temperature storage recommendations for AVONEX. FDA action on this supplement is expected in the fall. These proposed enhancements for administering and storing AVONEX are being pursued in response to the requests of people with MS who are looking for convenient therapies.

About AVONEX

AVONEX is the most prescribed treatment for relapsing forms of multiple sclerosis worldwide (through November 2005), 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 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.