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                                                                   EXHIBIT 10.43

                                 PROMISSORY NOTE

$250,000.00                              CAMBRIDGE, MASSACHUSETTS
                                         January 3, 2001

     FOR VALUE RECEIVED, the undersigned Paul Hamelin and Martha K. Hamelin
(hereinafter, collectively, "Borrower") hereby promises to pay to the order of
Millennium Pharmaceuticals, Inc., 75 Sidney Street, Cambridge, Massachusetts
02139 (hereinafter called the "Company") the principal amount of TWO HUNDRED
FIFTY THOUSAND DOLLARS ($250,000.00), together with interest on the outstanding
principal balance at a fixed rate of 5.87% annually, in the manner set forth
herein.

     Subject to the terms of this Note regarding acceleration of the repayment
of the principal amount, the principal amount of this Note shall be repayable by
the Borrower in four (4) equal annual instalments on the anniversary of the date
of this note, or if such anniversary is not a business day then on the first
business day thereafter, commencing January 3, 2002 with the final payment of
all principal outstanding hereunder and accrued interest, if any, on January 3,
2005.

     The principal amount remaining from time to time unpaid and outstanding
shall bear interest, both before and after the occurrence of an event of default
and before and after judgement to the date of the repayment in full of the
principal amount, at the rate specified above. Interest at such rate shall
accrue daily and be calculated on the basis of the actual number of days elapsed
in a year of 365 days or 366 days, as the case may be, and shall be payable
annually, in arrears, on the first anniversary of the date of this note
commencing January 3, 2002, or if such anniversary is not a business day then on
the first business day thereafter. Overdue interest shall bear interest at the
same rate, calculated as aforesaid.

     The funds advanced to the Borrower hereunder shall be used by the Borrower
exclusively for the purpose of acquiring the Property (as defined below) and for
no other purpose.

     At the option of the Company all outstanding sums advanced to the Borrower
pursuant to this Note shall become immediately due and payable, without notice
or demand, upon the termination for any reason, including death, of the
Borrower's employment with the Company or any of its subsidiaries. In the event
of such termination, the Company shall have the right to set off any amounts
which the Borrower owes the Company hereunder against any monies which the
Company or any of its subsidiaries may owe to the Borrower, of any nature
whatsoever, including without limitation, any compensation and any severance
owed as an employee of the Company or any of its subsidiaries or any other
benefit owed or held by the Borrower as an employee of the Company or any of its
subsidiaries and the Borrower hereby agrees to and authorize any such setoff.
For purposes of this paragraph and the following two paragraphs only, the term
"Borrower" shall refer only to Paul Hamelin where the context so requires.

     The indebtedness evidenced by this Note is secured by a Mortgage on certain
real estate located at 51 Nutmeg Lane, N. Andover, MA 01845 (the "Property")
which Mortgage will be duly executed and delivered to the Company by the
Borrower upon the Company's request, and the Borrower will obtain any consents
necessary to secure such Mortgage. The Borrower represents, warrants and
covenants that

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there will be no other liens on the Property except as reflected on Schedule 1
hereto. Reference is made to the Mortgage for additional rights of the Company
to accelerate the indebtedness evidenced by this Note. This Note shall become
immediately due and payable, without notice or demand, if the Borrower fails to
execute and deliver such Mortgage as required herein and, in such event, the
Company shall have the right to set off any amounts which the Borrower owes the
Company hereunder against any monies which the Company or any of its
subsidiaries may owe to the Borrower, of any nature whatsoever, including
without limitation, any compensation and any severance owed as an employee of
the Company or any of its subsidiaries or any other benefit owed or held by the
Borrower as an employee of the Company or any of its subsidiaries and the
Borrower hereby agrees to and authorizes any such setoff.

     If the payment of principal on this Note is not paid in accordance with the
terms aforementioned, then this Note shall be deemed to be in default and (i)
the Company shall have the right to set off any amounts which may be due to the
Company hereunder or under the Mortgage from any monies which the Company may
owe to the Borrower at any time, of any nature whatsoever, including without
limitation, any compensation and any severance owed as an employee of the
Company or any of its subsidiaries or any other benefit owed or held by the
Borrower as an employee of the Company or any of its subsidiaries and the
Borrower hereby agrees to and authorize any such setoff and (ii) if suit is
brought to collect this Note and if foreclosure proceedings are instituted with
respect to the Mortgages referred to herein, the Company shall be entitled to
collect, in addition to any principal outstanding hereunder, all costs and
expenses incurred by it in connection with such collection, to include, but not
necessarily be limited to, attorneys' fees and expenses.

     The Borrower shall have the right to prepay the principal of this Note, in
whole or in part, at any time or times, without penalty.

     Presentment, notice of dishonor and protest are hereby waived by the
Borrower. This Note shall be binding upon the Borrower and the Borrower's heirs,
executors, administrators and legal representatives.

     No delay or omission on the part of the Company in exercising any rights
hereunder shall operate as a waiver of such rights or of any other right of the
Company, nor shall any delay, omission or waiver on any one occasion be deemed
as a bar to or waiver of the same or any other right on any future occasion.
This Note may not be changed or terminated orally.

     All rights and obligations hereunder shall be governed by, and construed
and enforced in accordance with, the substantive laws of The Commonwealth of
Massachusetts, and this Note is executed as, and shall have effect of, a sealed
instrument.

     If any provision of this transaction is inconsistent with the laws and
statutes of The Commonwealth of Massachusetts, the rest of the transaction shall
not be affected, and that part that is not in accord with the said laws shall be
adjusted to so comply.


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     IN WITNESS WHEREOF, the undersigned have executed this Note as an
instrument under seal this third day of January, 2001.


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                                           /s/ PAUL HAMELIN
                                               Paul Hamelin


                                           /s/ MARTHA K. HAMELIN
                                               Martha K. Hamelin


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                                   SCHEDULE 1

                              Liens on the Property


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