November 1, 1999


North American Vaccine, Inc.
10150 Old Columbia Road
Columbia, Maryland  21046
Attention:  Dr. Randal Chase
            Chief Executive Officer and President


      Re:   $30,000,000 Senior Credit Facility


Dear Dr. Chase:

Bank of America,  N.A.  ("Bank of America")  is pleased to offer North  American
Vaccine,  Inc., a Canadian  corporation (the  "Borrower"),  a $30 million Senior
Secured Credit  Facility (the  "Facility").  Bank of America is pleased to offer
its  commitment  to lend up to $30  million,  upon and  subject to the terms and
conditions of this letter and the letter loan agreement dated  November 1, 1999
(the "Loan Agreement")  delivered by Bank of America and acknowledged and agreed
to by Borrower and Guarantor.

This letter is delivered to you in connection  with the Loan  Agreement.  Unless
otherwise  defined herein,  capitalized  terms shall have the meanings set forth
therein.  The  execution  and  delivery  of this  letter is a  condition  to the
effectiveness of the Loan Agreement. In connection with, and in consideration of
the agreements set forth in the Loan Agreement, the Borrower agrees with Bank of
America as follows:

      STRUCTURING FEE. At  Closing, the Borrower will pay a  structuring  fee of
      $25,000 to Bank of America for its own account.

By  acceptance  of this  letter,  the  Borrower  agrees  to pay  all  reasonable
out-of-pocket  fees  and  expenses  (including  reasonable  attorneys'  fees and
expenses and the allocated cost of internal  counsel)  incurred  before or after
the date hereof by us in connection  with the Facility;  provided that the legal
fees and expenses of internal  counsel at Bank of America in connection with the
Closing  of the  Facility  shall be covered by the  structuring  fee  referenced
above. The structuring fee payable above shall be fully-earned upon becoming due
and payable,  shall be non-refundable  for any reason whatsoever and shall be in
addition to any other fee, cost or expense payable pursuant to the Facility.






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North American Vaccine, Inc.
November 1, 1999
Page 2


The terms of this  letter  are  confidential  and,  except for  disclosure  on a
confidential  basis  to  your  accountants,  attorneys  and  other  professional
advisors  retained by you in connection  with the Facility or as may be required
by law,  may not be  disclosed in whole or in part to any other person or entity
without our prior written consent.









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North American Vaccine, Inc.
November 1, 1999
Page 3




Very truly yours,


BANK OF AMERICA, N.A.


By:     /s/ Lawrence J. Gordon
        ----------------------------------
Name:   Lawrence J. Gordon
Title:  Vice President


Accepted and Agreed to
as of November 1, 1999:



NORTH AMERICAN VACCINE, INC., as Borrower


By:    /s/ Randal Chase
       -----------------------------------
Name:  Randal Chase, Ph.D.
       -------------------
Title: Chief Executive Officer & President
       -----------------------------------



BAXTER INTERNATIONAL INC., as Guarantor


By:    /s/ Steven J. Meyer
       -----------------------------------
Name:  Steven J. Meyer
Title: Corp. Treasurer