<PAGE>
                                                                    EXHIBIT 99.1


BIOGEN, INC.
BIOGEN SAVINGS PLAN
FINANCIAL STATEMENTS AND SUPPLEMENTAL SCHEDULES
DECEMBER 31, 2001 AND 2000
<PAGE>
BIOGEN, INC.
BIOGEN SAVINGS PLAN
INDEX TO FINANCIAL STATEMENTS AND SUPPLEMENTAL SCHEDULES
------------------------------------------------------------------------------

<TABLE>
<CAPTION>
                                                                                    PAGE
<S>                                                                                 <C>
Report of Independent Accountants                                                     1

Statement of Assets Available for Plan Benefits as of December 31, 2001 and 2000      2

Statements of Changes in Assets Available for Plan Benefits for the Years Ended
  December 31, 2001 and 2000                                                          3

Notes to Financial Statements                                                        4-8

Supplemental Schedules*:

   Schedule I - Schedule of Assets Held for Investment Purposes at End of Year
     as of December 31, 2001                                                          9

   Supplemental Schedule II - Schedule of Reportable Transactions for the
     Year Ended December 31, 2001                                                    10
</TABLE>


* Other schedules have been omitted because such schedules are not applicable.
<PAGE>
                        REPORT OF INDEPENDENT ACCOUNTANTS


To the Participants and Administrator
of the Biogen Savings Plan

In our opinion, the accompanying statements of assets available for plan
benefits and the related statements of changes in assets available for plan
benefits present fairly, in all material respects, the assets available for plan
benefits of the Biogen Savings Plan (the "Plan") at December 31, 2001 and 2000,
and the changes in assets available for plan benefits for the years then ended
in conformity with accounting principles generally accepted in the United States
of America. These financial statements are the responsibility of the Plan's
management; our responsibility is to express an opinion on these financial
statements based on our audits. We conducted our audits of these statements in
accordance with auditing standards generally accepted in the United States of
America, which require that we plan and perform the audit to obtain reasonable
assurance about whether the financial statements are free of material
misstatement. An audit includes examining, on a test basis, evidence supporting
the amounts and disclosures in the financial statements, assessing the
accounting principles used and significant estimates made by management, and
evaluating the overall financial statement presentation. We believe that our
audits provide a reasonable basis for our opinion.

Our audits were conducted for the purpose of forming an opinion on the basic
financial statements taken as a whole. The Supplemental Schedules I and II are
presented for the purpose of additional analysis and are not a required part of
the basic financial statements but are supplementary information required by the
Department of Labor's Rules and Regulations for Reporting and Disclosure under
the Employee Retirement Income Security Act of 1974. These supplemental
schedules are the responsibility of the Plan's management. The supplemental
schedules have been subjected to the auditing procedures applied in the audits
of the basic financial statements and, in our opinion, are fairly stated in all
material respects in relation to the basic financial statements taken as a
whole.


June 14, 2002

PricewaterhouseCoopers LLP
Boston, Massachusetts
<PAGE>
BIOGEN, INC.
BIOGEN SAVINGS PLAN
STATEMENT OF ASSETS AVAILABLE FOR PLAN BENEFITS
DECEMBER 31, 2001 AND 2000
-------------------------------------------------------------------------------
<TABLE>
<CAPTION>
                                                             2001                2000
<S>                                                     <C>                <C>
Assets

Investments at fair value:
 Mutual funds:
  Fidelity Intermediate Bond Fund                         $ 1,632,995        $ 1,301,556
  Fidelity Puritan Fund                                     6,014,678 *        5,685,899 *
  Fidelity Value Fund                                       1,847,441            960,195
  Fidelity Magellan Fund                                   11,541,258 *       12,113,732 *
  Fidelity Retirement Government Money Market Fund          2,560,667          1,969,913
  Fidelity Growth Company Fund                             13,015,719 *       15,783,298 *
  Fidelity International Growth & Income Fund                   6,389             11,408
  Fidelity Asset Manager Growth Fund                        1,601,223          1,491,133
  Spartan US Equity Index Fund                              4,224,140 *        4,272,674 *
  Spartan International Index Fund                            106,032             33,993
  Fidelity US Bond Index Fund                               1,320,628            647,237
  Fidelity Low-Priced Stock Fund                            1,986,433            891,672
  USAA International Fund                                     776,856            932,954
  Janus Worldwide Fund                                      2,958,086          3,639,988 *
                                                          -----------        -----------
   Total mutual funds                                      49,592,545         49,735,652
                                                          -----------        -----------
Biogen, Inc. Stock Fund:
  Biogen, Inc. common stock                                15,618,183 *       14,756,816 *
  Interest bearing cash                                       351,311            380,131
                                                          -----------        -----------
   Total Biogen, Inc. Stock Fund                           15,969,494         15,136,947
                                                          -----------        -----------
Loans to participants                                         803,217            825,095
                                                          -----------        -----------
   Total investments                                       66,365,256         65,697,694
                                                          -----------        -----------
Receivables:
  Investment income receivable                                  1,113              1,864
  Receivable for investments sold                                  --             15,327
                                                          -----------        -----------
   Total receivables                                            1,113             17,191
                                                          -----------        -----------
Assets available for plan benefits                        $66,366,369        $65,714,885
                                                          ===========        ===========
</TABLE>

* Represents 5% or more of assets available for plan benefits.

   The accompanying notes are an integral part of these financial statements.

                                       2
<PAGE>
BIOGEN, INC.
BIOGEN SAVINGS PLAN
STATEMENT OF CHANGES IN ASSETS AVAILABLE FOR PLAN BENEFITS
FOR THE YEARS ENDED DECEMBER 31, 2001 AND 2000
-------------------------------------------------------------------------------
<TABLE>
<CAPTION>
                                                           2001               2000
<S>                                                  <C>                  <C>
Additions:
 Investment income;
  Net depreciation of investments:
   Mutual funds                                      $ (7,353,565)        $ (6,348,603)
   Biogen, Inc. common stock                             (671,278)          (4,947,230)
                                                     ------------         ------------
       Total net depreciation of investments           (8,024,843)         (11,295,833)
                                                     ------------         ------------
Dividends and interest:
  Mutual funds                                            973,943            3,582,519
  Biogen, Inc. Stock Fund interest bearing cash            19,410               25,796
                                                     ------------         ------------
       Total dividends and interest                       993,353            3,608,315
                                                     ------------         ------------
Contributions;
  Employer contributions                                1,223,138            1,039,943
  Participant contributions                             7,357,102            6,306,950
  Participant rollovers                                 1,263,868            1,754,222
                                                     ------------         ------------
       Total contributions                              9,844,108            9,101,115
                                                     ------------         ------------
       Total additions                                  2,812,618            1,413,597
                                                     ------------         ------------
Deductions:
  Benefits paid to participants                           319,076              272,024
  Participant rollovers                                 1,841,970            3,900,000
  Administrative fees                                          88                  200
                                                     ------------         ------------
       Total deductions                                 2,161,134            4,172,224
                                                     ------------         ------------
       Net increase (decrease)                            651,484           (2,758,627)

Assets available for plan benefits:
  Beginning of year                                    65,714,885           68,473,512
                                                     ------------         ------------
  End of year                                        $ 66,366,369         $ 65,714,885
                                                     ============         ============
</TABLE>

   The accompanying notes are an integral part of these financial statements.


                                       3
<PAGE>
BIOGEN, INC.
BIOGEN SAVINGS PLAN
NOTES TO FINANCIAL STATEMENTS
------------------------------------------------------------------------------

1.       DESCRIPTION OF THE PLAN

         The following brief description of the Biogen Savings Plan (the "Plan")
         is provided for general information purposes only. Participants should
         refer to the Plan agreement for more complete information.

         GENERAL INFORMATION

         Biogen, Inc. (the "Company") established the Plan as a deferred
         profit-sharing plan under Section 401(a) of the Internal Revenue Code
         of 1986, effective January 1, 1987. The Plan is designed to allow
         eligible employees to accumulate savings for retirement in the Plan
         without paying income taxes until the savings are actually received.

         ADMINISTRATION OF THE PLAN

         The Plan is administered by the Savings Plan Committee (the "Plan
         Committee"), whose members are appointed by the Company. Fidelity
         Management Trust Company is the Plan trustee (the "Trustee").

         PARTICIPATION

         Participation in the Plan is voluntary. Each employee of the Company is
         eligible to participate in the Plan upon the attainment of age 21
         unless he/she is (a) a student employed on a temporary basis, (b) an
         employee of a non-U.S. subsidiary or division of the Company, or (c) a
         member of a collective bargaining unit.

         CONTRIBUTIONS

         Eligible employees may make savings deposits (as described below) to
         the Plan in whole percentages of their gross salary ranging from a
         minimum of 2% to a maximum of 18% (40% as of January 1, 2002), subject
         to certain limitations. For each pay period, the Company will make a
         matching contribution (as described below) of units of the Biogen Inc.
         Stock Fund equal in value to 25% of each employee's savings deposit up
         to a maximum of 6% of the employee's gross salary, subject to certain
         limitations. Effective April 1, 2002, matching contributions will be
         made into the same funds as selected by the participants for their own
         contributions, and not exclusively into the Biogen Stock Fund.
         Effective August 1, 2000, following the end of each plan year
         (beginning with the 1999 plan year), an additional true-up matching
         contribution may be made on behalf of an eligible participant who has
         not received the full benefit of the Company matching contribution.
         Effective January 1, 2002, eligible employees are allowed to contribute
         after-tax savings deposits to the Plan, subject to certain limitations.

         PARTICIPANT ACCOUNTS

         Fidelity Investments Institutional Operations Company, Inc. is the
         Plan's recordkeeper. Each participant's account is credited with the
         participant's contribution, the Company's matching contribution and
         Plan earnings. Allocations are based on participant earnings or account
         balances, as defined. The benefit to which a participant is entitled is
         the benefit that can be provided from the participant's vested account.


                                       4
<PAGE>
BIOGEN, INC.
BIOGEN SAVINGS PLAN
NOTES TO FINANCIAL STATEMENTS
------------------------------------------------------------------------------

         INVESTMENT OF CONTRIBUTIONS

         Company matching contributions are invested in the Biogen, Inc. Stock
         Fund. Effective April 1, 2002, matching contributions will be made into
         the same funds as selected by the participants for their own
         contributions, and not exclusively into the Biogen, Inc. Stock Fund.
         The Biogen, Inc. Stock Fund includes Biogen, Inc. stock and cash or
         short term investments for liquidity purposes. Employee contributions
         are invested at the direction of the employee in increments of 1% in
         any combination of the following investment options:

         -        An intermediate bond fund designed to earn a high level of
                  current return. It is invested in Fidelity's Intermediate Bond
                  Fund.

         -        A balanced fund designed to preserve principal balance by
                  investing in a diversified portfolio of high yielding stocks
                  and bonds. It is invested in Fidelity's Puritan Fund.

         -        A fund which seeks to provide capital appreciation from
                  investments in companies which are undervalued or which
                  possess valuable fixed assets. It is invested in Fidelity's
                  Value Fund.

         -        An aggressive growth fund invested which seeks to achieve
                  capital appreciation. It is invested in Fidelity's Magellan
                  Fund.

         -        A US government money market fund seeks high current earnings
                  while preserving capital and liquidity. It is invested in
                  Fidelity's Retirement Government Money Market Fund.

         -        A growth company fund which seeks to provide capital
                  appreciation from investments primarily in common stock of
                  companies with above-average growth characteristics. It is
                  invested in Fidelity's Growth Company Fund.

         -        An international equity fund which seeks capital growth,
                  current income and growth of income. It is invested in
                  Fidelity's International Growth & Income Fund.

         -        An asset allocation fund that seeks total return with reduced
                  risk over the long term. It is invested in Fidelity's Asset
                  Manager Growth Fund.

         -        A long term growth fund which seeks to provide investment
                  results that correspond to the total return performance of
                  common stock of companies publicly traded in the US. It is
                  invested in the Spartan US Equity Index Fund, a Fidelity
                  sponsored fund.

         -        A fund that seeks to provide investment results that
                  correspond to the total return of foreign stock markets. It is
                  invested in the Spartan International Index Fund, a Fidelity
                  sponsored fund.

         -        A corporate bond fund that seeks to replicate the price and
                  interest performance of the debt securities in the Lehman
                  Brothers Aggregate Bond Index. It is invested in Fidelity's US
                  Bond Index Fund.

         -        A fund which seeks to provide capital appreciation from
                  investments in companies which are undervalued or which are
                  out of favor with other investors and that could offer the
                  possibility for significant growth. It is invested in
                  Fidelity's Low-Priced Stock Fund.

                                       5
<PAGE>
BIOGEN, INC.
BIOGEN SAVINGS PLAN
NOTES TO FINANCIAL STATEMENTS
------------------------------------------------------------------------------


         -        A fund that seeks long term capital growth and current income
                  from investments in stocks of companies organized and
                  operating principally outside the United States. It is
                  invested in the USAA International Fund.

         -        A fund that seeks capital growth over the long term from
                  investments in common stocks of foreign and domestic
                  companies. It is invested in the Janus Worldwide Fund.

         -        A fund that pools money to buy shares of Biogen, Inc. stock
                  and cash or short-term investments. It is invested in the
                  Biogen, Inc. Stock Fund.

         Dividends, interest, and other distributions received in any fund are
         reinvested in the same fund.

         VESTING

         Participants are fully vested in their savings deposit accounts and
         rollover accounts at all times. Participants will vest in the
         employer's matching contribution at a rate of 25% for each year of Plan
         service and will be fully vested after four years of Plan service.
         Participants become 100% vested in employer's matching contributions
         upon retirement or termination of employment due to disability.

         BENEFIT PAYMENTS

         Distributions are generally payable at termination of employment due to
         retirement, disability, death or any other reason. Distribution
         payments are made in cash in a lump sum for employees' contributions
         and in whole shares of stock for Company matching contributions.
         Forfeitures of nonvested amounts are used to reduce the amount of
         future Company matching contributions.

         LOANS

         Participants may borrow against their savings deposits. Loans will bear
         a reasonable interest rate determined by the Company. Repayment of
         loans is made by direct withholdings of a participant's salary for a
         period not to exceed five years (ten years for a residential loan). The
         minimum loan amount is $1,000 and a participant may borrow up to a
         maximum of 50% of the participant's vested account balance or $50,000,
         whichever is smaller. There is no minimum service requirement for a
         participant to be eligible for a loan.

         PLAN AMENDMENT AND TERMINATION

         The Company has the right to amend, suspend or terminate the Plan, but
         may not do so in a way which would divest a participant of accrued
         vested benefits. If the Plan is terminated, the Trustee will distribute
         the assets held in the trust, after payment of expenses, in such a
         manner as the Plan Committee shall determine. The Company currently has
         no intention to terminate the Plan.


2.       SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES

         The preparation of financial statements in conformity with accounting
         principles generally accepted in the United States of America requires
         management to make estimates and assumptions that affect the reported
         amounts and disclosures in the financial statements. Actual results
         could differ from those estimates. The following is a summary of
         significant accounting policies which are in conformity with accounting
         principles generally accepted in the United States of America
         consistently followed by the Plan in the preparation of its financial
         statements.



                                       6
<PAGE>
BIOGEN, INC.
BIOGEN SAVINGS PLAN
NOTES TO FINANCIAL STATEMENTS
------------------------------------------------------------------------------


         BASIS OF ACCOUNTING

         The financial statements of the Plan are prepared on the accrual basis
         of accounting.

         INVESTMENTS

         Plan investments are stated at fair value. The Company stock is valued
         at its quoted market price. Mutual fund investments are valued at net
         asset value representing the value of which shares of the fund may be
         purchased or redeemed. Loans to participants are stated at principal
         plus accrued interest, which approximates fair value.

         Purchases and sales of securities are recorded on a trade-date basis.
         Cost is determined on the average cost basis. Net appreciation or
         depreciation, which includes realized and unrealized gains or losses on
         investments, is reflected for the year in the statement of changes in
         assets available for plan benefits. Interest income is recorded on the
         accrual basis. Dividends are recorded on the ex-dividend date.

         PAYMENT OF BENEFITS

         Benefits are recorded when paid.

         INCOME TAXES

         No provision for income taxes has been made in the financial statements
         as the Plan qualifies as a tax-exempt entity under Section 401 of the
         Internal Revenue Code ("Code"). The Plan has received a favorable
         determination letter dated June 5, 1996 from the Internal Revenue
         Service. The Plan has since been amended and a new letter has not been
         requested. Management has asserted the Plan, as amended, and its
         operations have been and continue to be in accordance with all
         applicable provisions of the Code and the Employee Retirement Income
         Security Act of 1974 ("ERISA").

         EXPENSES OF THE PLAN

         Administrative and audit fees are paid directly by the Company and,
         accordingly, such items are not reflected in the financial statements
         of the Plan. Expenses directly related to the investment transactions
         of the Plan are paid by the Plan.


3.       LOANS TO PARTICIPANTS

         At December 31, 2001 and 2000, the Plan had loans receivable from
         participants aggregating $803,217 and $825,095, respectively. Interest
         rates on the loans range from 6.5% to 9.5% annually. The loans are
         collateralized by the participant's interest in the Plan.


4.       PARTY-IN-INTEREST TRANSACTIONS

         The Plan invests in common stock of Biogen, Inc., the employer, and
         transactions in this common stock are party-in-interest transactions.
         During the years ended December 31, 2001 and 2000, the Plan purchased
         shares of the common stock having values of $1,885,797 and $4,209,260,
         respectively, and sold shares of the common stock having values of
         $1,759,867 and $3,656,278, respectively.

                                       7
<PAGE>
BIOGEN, INC.
BIOGEN SAVINGS PLAN
NOTES TO FINANCIAL STATEMENTS
------------------------------------------------------------------------------

         Certain of the Plan's assets are invested in mutual funds for which FMR
         Corp. provides investment advisory services. FMR Corp. is an affiliate
         of both Fidelity Management Trust Company and Fidelity Investments
         Institutional Operations Company, Inc. Accordingly, these transactions
         qualify as party-in-interest.


5.       NON-PARTICIPANT-DIRECTED INVESTMENT

         Information about the assets and the significant components of the
         changes in assets relating to the non-participant-directed investment
         is as follows:

<TABLE>
<CAPTION>
                                                       December 31,
                                                  2001               2000
<S>                                            <C>                <C>
Assets:
  Biogen, Inc. Stock Fund                      $l5,969,494        $15,136,947
  Receivables                                        1,113             17,191
                                               -----------        -----------
                                               $15,970,607        $15,154,138
                                               ===========        ===========
</TABLE>

<TABLE>
<CAPTION>
                                                                  Year Ended
                                                                  December 31,
                                                             2001               2000
<S>                                                      <C>                <C>
Changes in Assets:
  Employer contributions                                 $ 1,218,822        $ 1,039,943
  Participant contributions                                  901,085            719,034
  Interest                                                    19,410             23,230
  Net appreciation/(depreciation)                           (671,278)        (4,947,230)
  Transfer of investments from other options                (145,541)           332,470
  Benefits paid to participants                             (506,029)        (1,261,640)
                                                         -----------        -----------
                                                         $   816,469       $ (4,094,193)
                                                         ===========        ===========
</TABLE>



                                       8
<PAGE>
BIOGEN, INC.
BIOGEN SAVINGS PLAN
SCHEDULE OF ASSETS HELD FOR INVESTMENT PURPOSES
(SCHEDULE H, PART IV, ITEM 4i, FORM 5500)
DECEMBER 31,2001                                        SUPPLEMENTAL SCHEDULE I
--------------------------------------------------------------------------------

<TABLE>
<CAPTION>
 Number of
  Shares/                                                                                      Current
   Units                                                                   Cost                 Value
<S>             <C>                                                      <C>                <C>
   158,236      Fidelity Intermediate Bond Fund*                                            $  1,632,995
   340,389      Fidelity Puritan Fund*                                                         6,014,678
    35,866      Fidelity Value Fund*                                                           1,847,441
   110,739      Fidelity Magellan Fund*                                                       11,541,258
 2,560,667      Fidelity Retirement Government Money Market Fund*                              2,560,667
   244,564      Fidelity Growth Company Fund*                                                 13,015,719
       341      Fidelity International Growth & Income Fund*                                       6,389
   111,661      Fidelity Asset Manager Growth Fund*                                            1,601,223
   103,940      Spartan U.S. Equity Index Fund*                                                4,224,140
     4,338      Spartan International Index Fund*                                                106,032
   122,280      Fidelity US Bond Index Fund*                                                   1,320,628
    72,445      Fidelity Low-Priced Stock Fund*                                                1,986,433
    46,297      USAA International Fund                                                          776,856
    67,475      Janus Worldwide Fund                                                           2,958,086
                                                                                            ------------
                 Total mutual funds                                                           49,592,545
                                                                                            ------------
   272,331      Biogen, Inc. common stock*                               $ 8,437,235          15,618,183
                Interest bearing cash                                        351,311             351,311
                                                                                            ------------
                 Total Biogen, Inc. Stock Fund                                                15,969,494
                                                                                            ------------
                Loans to participants* 6.5% to 9.5%                                              803,217
                                                                                            ------------
                Total                                                                       $ 66,365,256
                                                                                            ============
</TABLE>

*        Party-in-interest.


                                       9
<PAGE>
BIOGEN, INC.
BIOGEN SAVINGS PLAN
SCHEDULE OF REPORTABLE TRANSACTIONS (INVOLVING AMOUNTS IN
EXCESS OF 5% OF CURRENT VALUE OF PLAN ASSETS)*
(SCHEDULE H, PART IV, ITEM 4j, FORM 5500)
YEAR ENDED DECEMBER 31, 2001                          SUPPLEMENTAL SCHEDULE II
-------------------------------------------------------------------------------
<TABLE>
<CAPTION>
                                                                                                          CURRENT
                                                                                                          VALUE ON
                                               PURCHASE     SELLING     LEASE    EXPENSE    HISTORICAL   TRANSACTION
PARTY INVOLVED   DESCRIPTION OF ASSET           PRICE        PRICE      RENTAL   INCURRED    COST            DATE        GAIN (LOSS)
<S>              <C>                         <C>          <C>          <C>       <C>       <C>           <C>            <C>
Biogen, Inc.     Biogen, Inc. common stock    $ 1,885,797  $      --    $   --    $   --    $       --     $1,885,797    $   --
Biogen, Inc.     Biogen, Inc. common stock        --        1,759,867       --        --     1,740,607      1,759,867     19,260
</TABLE>

*    Non-participant directed transactions in excess of 5% of the current value
     of the Plan's assets as of December 31, 2001 as defined by Section
     2520.103-6 of the Department of Labor's Rules and Regulations for Reporting
     and Disclosure under the Employee Retirement Security Income Act of 1974.



                                       10