EXHIBIT 99.1

Media Contact:
Amy McKnight
Associate Director, Public Affairs
Biogen, Inc.
Tel: (617) 914-6524


Investment Community Contact:
Elizabeth Woo
Senior Director, Investor Relations
Biogen, Inc.
Tel: (617) 679-2812



               BIOGEN ANNOUNCES IMPROVED PERFORMANCE EXPECTATIONS

                      FOR FIRST QUARTER AND FULL YEAR 2003

                                      - - -
                      FIRST QUARTER 2003 GUIDANCE INCREASED

              BASED ON ROBUST REVENUES AND OPERATIONAL EFFICIENCIES

                                      - - -
          FULL YEAR OPERATING 2003 GUIDANCE INCREASED TO $1.72 - $1.85

                                      - - -

For Immediate Release

Cambridge, MA (April 2, 2003) -- Biogen, Inc. (NASDAQ: BGEN) today announced
revised guidance for first quarter 2003 earnings per share which are now
expected to be in the range of $0.39 - $0.43. Included in this estimate are
$0.08 per share of one-time charges. First quarter operating earnings per share
are expected to be in the range of $0.47 - $0.51. This is an increase over the
previous guidance of $0.31 - $0.38 provided on January 28, 2003. Total revenues
for the first quarter are expected to be about $320 million.

Jim Mullen, Biogen's Chairman and CEO, commented, "As we entered 2003, it was
clear that our performance would hinge on our ability to execute on a series of
key goals:

- -     driving the AVONEX(R) (Interferon beta-1a) business

- -     leveraging the investments of the past two years to deliver efficiencies
      in research and development, as well as sales and marketing, and


                                       1



- -     launching AMEVIVE(R) (alefacept) and establishing a trajectory toward our
      3 year revenue goal.

Reviewing our first quarter results and trends, we've concluded that we are
already succeeding on our first two goals. It is still early, but the AMEVIVE
launch is progressing in line with our first quarter goals. The number of
physicians expressing interest during the first eight weeks of launch has
exceeded our expectations."

At the end of March, over 600 physicians have initiated nearly 2,000 patients
into the process of insurance verification. As with any new in-office injectable
therapy, the reimbursement process can take several weeks. Among patients who
have completed this process, more than 90 percent have received coverage for
AMEVIVE. As planned, the Company expects AMEVIVE dosing to gain even more
momentum over the next quarter with increased revenue ramp in the second half of
the year as the reimbursement process accelerates, and physicians become more
familiar with a novel in-office injectable.

Accordingly, the Company anticipates that these first quarter trends will lead
the full year operating performance to the favorable end of the guidance ranges
in the revenue and operating expense line items issued on January 28, 2003. As a
result, the Company has updated its full year 2003 operating earnings per share
guidance upwards to $1.72 - $1.85 from its prior guidance of $1.63 - $1.78.
Guidance for full year 2003 reported earnings per share, which is the most
comparable GAAP-based financial measure to operating earnings per share, is not
currently accessible as the Company cannot predict with any certainty the nature
or the amount of non-operating or unusual charges for subsequent quarters. The
Company does, however, anticipate that it may have to take such charges in
subsequent quarters and that such charges, if material, would cause reported
earnings per share to differ from operating earnings per share.

Net income for 2002 was $199 million, or $1.31 per share, which included $0.28
per share of net non-operating or unusual charges. Excluding these charges, 2002
operating earnings were $242 million, or $1.59 operating earnings per share.

A full review of the first quarter results and an update on the progress of the
AMEVIVE launch will be provided on the first quarter earnings conference call on
April 17, 2003.

ABOUT BIOGEN

Biogen is the world's oldest independent biotechnology company and 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.

                                       2


FORWARD LOOKING STATEMENTS / SAFE HARBOR

This press release contains forward-looking statements regarding expected future
financial results. These statements are based on the Company's current beliefs
and expectations. A number of risks and uncertainties could cause actual results
to differ materially. For example, financial results, including earnings per
share, expenses, revenues, revenue growth, income tax rate, royalties and
capital expenditures, may be affected by the impact of competitive products on
AVONEX sales, any slowing of growth of the multiple sclerosis market, any change
in market acceptance of AVONEX in key markets worldwide, the Company's ability
to achieve market acceptance of AMEVIVE and successfully launch AMEVIVE in the
U.S., the impact of reimbursement and pricing decisions related to AMEVIVE, the
impact of competitive products on AMEVIVE sales, the impact of litigation, any
unanticipated increase in expenses including in the areas of research and
development and sales and marketing, and in-licensing and product opportunities.

For more detailed information on the risks and uncertainties associated with
these forward looking statements and the Company's other activities see the
Outlook section in MD&A of the Company's Annual Report on Form 10-K and
quarterly reports on Form 10-Q filed with the Securities and Exchange
Commission. The Company does not undertake any obligation to publicly update any
forward-looking statements.