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                                                                   EXHIBIT 10.47

             EXECUTIVE SEVERANCE -- SENIOR/EXECUTIVE VICE PRESIDENT

     As a Senior Vice President or Executive Vice President, you are entitled to
severance benefits in the event your employment with Biogen is terminated by
Biogen other than for cause. The severance benefits will be comprised of (i) a
lump sum payment and (ii) upon completion of the appropriate forms, continuation
at Biogen's expense of your participation in Biogen's group medical and dental
insurance plans. The lump sum payment, equivalent to at least nine months of
annual base salary and a prorated portion of your target annual performance
bonus, will be calculated as follows:

                      [9 + (A x 2)] x B = lump sum payment

where: A  is number of full years of service with Biogen, but (A x 2) not more
          than 9
       B  is monthly annual compensation (i.e., one-twelfth of sum of annual
          base salary plus target annual performance bonus modified by your most
          recent individual performance incentive factor).

The lump sum payment (less state and federal income and welfare taxes and other
mandatory deductions under applicable laws) will be paid to you promptly
following the termination of your employment with Biogen. Your participation in
Biogen's group medical and dental insurance plans will continue until the
earlier of (x) the date you become eligible to participate in the medical and
dental insurance plans of a third party employer or (y) the date that is [9 + (A
x 2)] months following the termination of your employment with Biogen; and only
to the same extent such insurance is then provided to regular employees of
Biogen. For example:

          If your employment with Biogen is terminated after two months, you
          will receive a lump sum payment equal to nine months of your monthly
          annual compensation and continue to participate in Biogen's group
          medical and dental plans for nine months, unless you become eligible
          to participate in a third party employer's medical and dental plans
          before that date.

          If your employment with Biogen is terminated after five years, you
          will receive a lump sum payment equal to 18 months of your monthly
          annual compensation and continue to participate in Biogen's group
          medical and dental plans for 18 months, unless you become eligible to
          participate in a third party employer's medical and dental plans
          before that date.

For purposes of the severance arrangement, "cause" means (i) your engagement in
misconduct that is injurious to Biogen monetarily or otherwise, (ii) your
conviction of a felony by a court of competent jurisdiction, (iii) your
commission of any act of fraud or embezzlement relating to the property of
Biogen, or (iv) your material violation of any obligations of confidentiality
and nondisclosure owed to Biogen.

Payment and provision of the severance benefits described above are conditioned
on your execution of a general release in favor of Biogen, in form and substance
reasonably acceptable to Biogen, in respect of any and all claims relating to
your employment and the termination of your employment with Biogen. If you
retire or terminate your employment with Biogen or Biogen terminates your
employment for cause or you do not provide the requisite general release, then
you shall not be entitled to receive the severance benefits described above.<PAGE>
                              [BIOGEN LETTERHEAD]

                                                                   EXHIBIT 10.48

                                         May 19, 1998
                                                           REVISED

Ms. Sylvie Gregoire
78 rue Charles Laffitte
92200 Neuilly Sur Seine
FRANCE

Dear Sylvie:

This letter confirms our discussion regarding your temporary transfer to the US
headquarters in the role of Program Executive. Your annual salary will be
$140,000 with continued participation in the Executive Bonus Plan. As in the
past, you will be eligible to receive a target bonus of fifteen (15) percent of
base salary.

To facilitate your move from Paris to Boston, a relocation package will be
provided which includes the movement of your household/personal effects, the
services of a relocation firm, and reimbursement of all reasonable expenses
associated with your move. This includes real-estate agent, legal and other
closing costs associated with the purchase of your new residence in the Boston
area; and up to 60 days temporary living in the Boston area pending the
availability of your new residence. To further assist you with your relocation,
Biogen will provide you with a one time relocation payment of $20,000.

You will be entitled to participate in the US benefits program and you will be
able to choose from a menu of benefit options through our flexible benefits
program, BioChoice. These include health care, life, dependent life, and
disability insurance as well as two flexible spending accounts, Med-Flex and
D-Flex, for eligible medical or dependent care expenses. At the beginning of the
calendar quarter following your date of transfer, you will be eligible to
participate in Biogen's pension and 401(k) savings plans. You are also entitled
to fifteen (15) vacation days. Biogen also offers a variety of additional
benefits including group homeowners and automobile insurance. As part of your
benefits package, Biogen will provide you assistance for tax planning and
support of your 1998 tax returns. Your eligibility for and participation in the
European benefit programs will cease upon your transfer to the US headquarters.

As discussed, upon your transfer to Cambridge, the Company will subsidize the
tuition costs for your son to attend the French school for up to two years
($8,500 per year).

To facilitate your temporary transfer to the US headquarters, Biogen will
provide counsel and assistance to you and your household members in securing the
necessary documentation to reside and work in the United States. I understand
Biogen's immigration counsel already has contacted you to address this matter.

On behalf of Jim Tobin, congratulations and best wishes for continued success at
Biogen.

                                        Sincerely,

                                        /s/ Frank A. Burke, Jr.
                                        ----------------------------------------
                                        Frank A. Burke, Jr.
                                        Vice President, Human Resources

/bk
cc: Mr. James R. Tobin<PAGE>
                              [BIOGEN LETTERHEAD]

                                                                   EXHIBIT 10.49

                                                August 8, 2001

Ms. Sylvie Gregoire
9 Prospect Street
Winchester, MA 01890

Dear Sylvie:

I am pleased to advise you that the Compensation and Management Resources
Committee has approved your appointment as Executive Vice President, Technical
Operations, reporting to me. Effective July 19, 2001, your annual base salary is
increased to $325,000 and your target bonus is increased to 50% of base salary
under Biogen's management incentive plan. Effective August 8, 2001, the Stock
and Option Plan Administration Committee has granted you an option to purchase
up to 150,000 shares of Biogen's common stock, with a four year, straight-line
vesting schedule. You will next be eligible for both a salary adjustment and
merit stock option grant at year-end 2002.

On behalf of the Board of Directors, please accept our congratulations and best
wishes for success in this important new role. I look forward to your
significant leadership and contributions as we continue to build Biogen.

Best personal regards.

                                        Sincerely,

                                        /s/ James C. Mullen
                                        ----------------------------------------
                                        James C. Mullen
                                        President and Chief Executive Officer

JCM:bk
cc: Personnel File<PAGE>
                                                                   EXHIBIT 10.50

                                                 VICE PRESIDENT, HUMAN RESOURCES

                                                October 19, 2001

Sylvie Gregoire
9 Prospect Street
Winchester, MA 01890

Dear Sylvie:

On July 19, 2001, you were promoted to the Executive Vice President level of
Biogen. At that time we were in the process of conducting a comprehensive review
of the compensation and benefits associated with your promotion.

I am pleased to confirm the full list of benefits that accompany this promotion.

TARGET BONUS: Your incentive target is 50% of your base salary.

LONG TERM INCENTIVES: Biogen has adopted a new approach to communicating and
granting stock options to employees. You will be eligible for an annual merit
stock option grant, based on a design which emphasizes the future expected value
of the grant. The details of how we will communicate and value options will be
outlined in December.

CHANGE OF CONTROL: You have been designated as a "Designated Employee" for
purposes of Biogen's 1985 Non-Qualified Stock Option Plan. If at any time within
two years following a Corporate Transaction (as defined in the stock option
plan) your employment with Biogen is terminated by Biogen other than for cause,
then each outstanding option held by you will automatically accelerate so that
the option immediately becomes fully exercisable and may be exercised for a
period of one year following the termination of your employment or, if earlier,
until the expiration of the option. Please read the stock option plan for more
details about the rights of a Designated Employee in the event of a Corporate
Transaction and any applicable limitations.

VACATION: You are entitled to an additional week of vacation each year. This w~k
is over and above the company's normal vacation schedule (which is based upon
years of service).

SUPPLEMENTAL SAVINGS PLAN: You will be entitled to participate in the Voluntary
Executive Supplemental Savings Plan. This plan allows participants to defer
[pretax] base salary and future bonuses. Enrollment in this plan takes place in
December each year. You will be provided additional information on the plan at
that time.

LIFE INSURANCE: You will have life insurance coverage that is the greater of
$1,000,000 or three times your annual salary and subject to the normal medical
standards of the life insurance policy.

<PAGE>
SEVERANCE: You will have a minimum severance benefit that is the greater of the
severance outlined in your letter dated January 7, 2000 or the severance
outlined in the Executive Severance document, which has been included with this
letter.

EXECUTIVE STOCK OWNERSHIP: You will be expected to acquire and maintain a
personal financial interest in Biogen. Ownership is defined as stock held
outright, stock held in the 401(k) plan and stock held under the Employee Stock
Purchase Plan. Vested but unexercised shares would also be counted toward
ownership guidelines. You will be required to maintain a financial interest of
six times base salary. You will have a five-year period from the date of your
appointment to Vice President to obtain this ownership level.

TAX PREPARATION: You are eligible to have your federal and state income taxes
prepared by PricewaterhouseCoopers.

On behalf of Jim Mullen, please accept my sincere congratulations and best
wishes for future success with Biogen.

                                                Sincerely,

                                                /s/ Frank A. Burke, Jr.

                                                Frank A. Burke, Jr.

/bk
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