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                                   EXHIBIT 4.1

                   AMENDED AND RESTATED FACILITY ONE TERM NOTE


$5,000,000.00                                              Boston, Massachusetts
                                                              As of May 21, 1997

        FOR VALUE RECEIVED, the undersigned GelTex Pharmaceuticals, Inc., a
Delaware corporation (the "Borrower") hereby promises to pay to the order of
FLEET NATIONAL BANK (the "Bank") the principal amount of Five Million and 00/100
($5,000,000.00) Dollars or such portion thereof as may be advanced by the Bank
pursuant to ss.1.2 of that certain letter agreement dated May 21, 1997 between
the Bank and the Borrower, as amended (as so amended, the "Letter Agreement")
and remains outstanding from time to time hereunder ("Principal"), with
interest, at the rate hereinafter set forth, on the daily balance of all unpaid
Principal, from the date hereof until payment in full of all Principal and
interest hereunder.

        Interest on all unpaid Principal shall be due and payable monthly in
arrears, on the first day of each month, commencing on the first such date after
the advance of any Principal and continuing on the first day of each month
thereafter and on the date of payment of this note in full, at a fluctuating
rate per annum (computed on the basis of a year of three hundred sixty (360)
days for the actual number of days elapsed) which shall at all times be equal to
the Prime Rate, as in effect from time to time (but in no event in excess of the
maximum rate permitted by then applicable law), with a change in the aforesaid
rate of interest to become effective on the same day on which any change in the
Prime Rate is effective; provided, however, that (A) if a Eurodollar Interest
Rate (as defined in the Letter Agreement) shall have become applicable to all or
any portion of the outstanding Principal for any Interest Period (as defined in
the Letter Agreement), then interest on such Principal or portion thereof shall
accrue at said applicable Eurodollar Interest Rate for such Interest Period and
shall be payable on the Interest Payment Date (as defined in the Letter
Agreement) applicable to such Interest Period, and (B) if a COF Interest Rate
(as defined in the Letter Agreement) shall have become applicable to the
outstanding Principal, then interest on the outstanding Principal shall accrue
at said COF Interest Rate and shall be paid on the first day of each month.
Overdue Principal and, to the extent permitted by law, overdue interest shall
bear interest at a fluctuating rate per annum which at all times shall be equal
to the sum of (i) four (4%) percent per annum plus (ii) the per annum rate
otherwise payable under this note with respect to the Principal which is overdue
(or as to which such interest is overdue) (but in no event in excess of the
maximum rate permitted by then applicable law), compounded monthly and payable
on demand. As used herein, "Prime Rate" means the variable rate of interest per
annum designated by the Bank from time to time as its prime rate, it being
understood that such rate is merely a reference rate and does not necessarily
represent the lowest or best rate being charged to any customer. If the entire
amount of any required Principal and/or interest is not paid within ten (10)
days after the same is due, the Borrower shall pay to the Bank a late fee equal
to five percent (5%) of the required payment, provided that such late fee shall
be reduced to three percent (3%) of any required Principal and 





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interest that is not paid within fifteen (15) days of the date it is due if this
note is secured by a mortgage on an owner-occupied residence of 1-4 units.

        The outstanding Principal of this note shall be repaid by the Borrower
to the Bank in the following installments: (i) 5 equal consecutive monthly
payments of $103,958.40 each, payable on the last day of each month during the
period January - May 1998; followed by (ii) 17 equal consecutive quarterly
payments of $248,345.06 each, payable on the last day of each calendar quarter
commencing June 30, 1998 and continuing through and including June 30, 2002;
followed by (iii) an 18th and final quarterly payment due on September 30, 2002
in an amount equal to all then remaining Principal and all interest accrued but
unpaid thereon.

        The Borrower may at any time and from time to time prepay all or any
portion of any Facility One Term Loan (as defined in the Letter Agreement), but,
as to Fixed Rate Loans (as defined in the Letter Agreement), only at the times
and in the manner, and (under certain circumstances) with the additional
payments, provided for in the Letter Agreement. Any prepayment of Principal, in
whole or in part, will be without premium or penalty (but, in the case of Fixed
Rate Loans, may require payment of additional amounts, as provided for in the
Letter Agreement). Each Principal prepayment shall be accompanied by payment of
all interest on the prepaid amount accrued but unpaid to the date of payment.
Any partial prepayment of Principal will be applied against Principal
installments in inverse order of normal maturity.

        Payments of both Principal and interest shall be made, in lawful money
of the United States in immediately available funds, at the office of the Bank
located at One Federal Street, Boston, Massachusetts 02110, or at such other
address as the Bank may from time to time designate.

        The undersigned Borrower irrevocably authorizes the Bank to make or
cause to be made, on a schedule attached to this note or on the books of the
Bank, at or following the time of making any Facility One Term Loan and of
receiving any payment of Principal, an appropriate notation reflecting such
transaction (including date, amount and maturity) and the then aggregate unpaid
balance of Principal. Failure of the Bank to make any such notation shall not,
however, affect any obligation of the Borrower hereunder or under the Letter
Agreement. The unpaid Principal amount of this note, as recorded by the Bank
from time to time on such schedule or on such books, shall constitute
presumptive evidence of the aggregate unpaid principal amount of the Facility
One Term Loans.

        The Borrower hereby (a) waives notice of and consents to any and all
advances, settlements, compromises, favors and indulgences (including, without
limitation, any extension or postponement of the time for payment), any and all
receipts, substitutions, additions, exchanges and releases of collateral, and
any and all additions, substitutions and releases of any person primarily or
secondarily liable, (b) waives presentment, demand, notice, protest and all
other demands and notices generally in connection with the delivery, acceptance,
performance, default or enforcement of or under this note, and (c) agrees to
pay, to the extent permitted by law, all reasonable costs and expenses,
including, without limitation, reasonable attorneys' fees, 


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incurred or paid by the Bank in enforcing this note and any collateral or
security therefor, all whether or not litigation is commenced.

        This note is the Facility One Term Note referred to in the Letter
Agreement. This note is subject to prepayment as set forth in the Letter
Agreement. The maturity of this note may be accelerated upon the occurrence of
an Event of Default, as provided in the Letter Agreement.

        THE BORROWER HEREBY KNOWINGLY, VOLUNTARILY AND INTENTIONALLY WAIVES THE
RIGHT TO A TRIAL BY JURY IN RESPECT OF ANY CLAIM BASED ON THIS NOTE OR ARISING
OUT OF, UNDER OR IN CONNECTION WITH THIS NOTE OR ANY RELATED DOCUMENTS OR OUT OF
ANY COURSE OF CONDUCT, COURSE OF DEALING, STATEMENTS (WHETHER ORAL OR WRITTEN)
OR ACTIONS OF ANY PERSON. THIS WAIVER CONSTITUTES A MATERIAL INDUCEMENT FOR THE
BANK TO ACCEPT THIS NOTE AND TO MAKE THE FACILITY ONE TERM LOANS AS CONTEMPLATED
IN THE LETTER AGREEMENT.

        Executed, as an instrument under seal, as of the day and year first
above written.


CORPORATE SEAL                        GELTEX PHARMACEUTICALS, INC.


ATTEST:

/s/ Elizabeth A. Grammer              By: /s/ Paul J. Mellett
-----------------------------             --------------------------------------
Secretary                                 Name: Paul J. Mellett, Jr.
                                          Title: Vice President, Administration
                                                   and Finance








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