BIOGEN ANNOUNCES RESULTS OF PHASE II TRIALS WITH ADENTRI (TM) AT AMERICAN HEART ASSOCIATION MEETING

Biogen (NASDAQ: BGEN) today announced positive results of a Phase II study of oral ADENTRI, an adenosine receptor antagonist, in patients with stable heart failure. The results were announced at the annual meeting of the American Heart Association, which is being held this week in Orlando, Florida.

“We are very pleased with the results of our Phase II trial of oral ADENTRI and plan to meet with the FDA to review these data in preparation for moving forward with the development of this promising compound,” said Burt Adelman, M.D., Biogen’s Executive Vice President of Research & Development.

The trial was a randomized, double blind, placebo-controlled study that evaluated the safety, pharmacology and clinical effects of oral ADENTRI among stable heart failure patients. Patients were maintained on their usual medications, including ACE inhibitors and diuretics, and were dosed with either placebo or one of four doses of ADENTRI, administered once daily for 10 days. The evaluation of safety, which was the primary endpoint of the study, did not reveal any significant safety concerns during the 10 days of dosing or during an additional 30 days of follow up. In addition, the study showed increases in sodium excretion above baseline and above placebo beginning on Day 1, and continuing over the 10-day dosing period. These effects were not accompanied by reductions in kidney function or substantial increases in potassium excretion.

ADENTRI is a novel adenosine receptor antagonist that has the potential to maintain renal function during standard heart failure therapy, while causing natriuresis (or sodium excretion).

About Biogen

Biogen is a leader in biologics research, development and manufacturing. A pioneer in leading edge research in immunology, neurobiology and oncology, Biogen brings novel therapies to improve patients’ lives around the world through its global marketing capabilities. For press releases and additional information about the company, please visit http://www.biogen.com.

This press release contains forward-looking statements regarding the expectations for development of ADENTRI. These statements are based on our current beliefs and expectations. Actual results could differ materially. 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 animal models or early stage clinical trials does not ensure that later stage or larger scale clinical trials will be successful. The results of studies of the product in larger clinical trials may not be as expected or safety issues or other problems or delays may arise during clinical trials. For more detailed information on the risks and uncertainties associated with these forward looking statements and Biogen’s other activities see the Outlook section in MD&A; of Biogen’s Annual Report on Form 10-K and Quarterly Reports on Form 10-Q filed with the SEC. Biogen does not undertake any obligation to publicly update any forward-looking statements.