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                                                                    Exhibit 10.3
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THIS SECURITY HAS NOT BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933, AS
AMENDED (THE "ACT"), OR APPLICABLE STATE SECURITIES LAWS AND MAY  NOT BE
TRANSFERRED OR OTHERWISE DISPOSED OF UNLESS IT HAS BEEN REGISTERED UNDER THE ACT
AND SUCH LAWS OR (1) REGISTRATION UNDER APPLICABLE STATE SECURITIES LAWS IS NOT
REQUIRED AND (2) AN OPINION OF COUNSEL SATISFACTORY TO ARONEX IS FURNISHED TO
ARONEX TO THE EFFECT THAT REGISTRATION UNDER THE ACT IS NOT REQUIRED.

                                PROMISSORY NOTE

$2,000,000                                                      9/13, 1996
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                                                            The Woodlands, Texas

 FOR VALUE RECEIVED, Aronex Pharmaceuticals, Inc., a Delaware corporation
("Aronex"), hereby unconditionally promises to pay to Genzyme Corporation
("Genzyme"), on 9/13, 1997 (the "Maturity Date"), the principal amount of Two
Million Dollars ($2,000,000), or such lesser amount as may be determined
pursuant to the second paragraph hereof, and to pay interest on the principal
amount of $2,000,000 to Genzyme at the rate of nine percent (9%) per annum from
the date hereof until paid in full, calculated on the basis of a 360-day year
for the actual number of days elapsed. Any payments of interest or principal
which are not paid when due shall bear interest at a rate equal to 2% per annum
above the rate of interest set forth in the prior sentence. This Note is issued
pursuant to Amendment No. 2 of the Stock Purchase Agreement dated 9/10, 1996
between Aronex and Genzyme (the "Advance Agreement") and is subject to all the
terms and conditions contained in, and is entitled to the benefits of, the
Advance Agreement. All capitalized terms used and not otherwise defined herein
shall have the meanings given to them in the Advance Agreement, the Stock
Purchase Agreement (as hereinafter defined) or the License and Development
Agreement (as hereinafter defined), as the case may be. The Stock Purchase
Agreement means the Common Stock Purchase Agreement dated as of September 10,
1993 between Aronex and Genzyme, as amended by Amendment No. 1 dated September
8, 1995 and as further amended by the Advance Agreement. The License and
Development Agreement means the License and Development Agreement dated as of
September 10, 1993 between Aronex and Genzyme, as amended by Amendment No. 1
dated September 8, 1995.

 All payments of principal and interest shall be made at the offices of Genzyme
set forth in the Stock Purchase Agreement and at the times set forth herein.
Principal amounts outstanding hereunder may not be prepaid, in whole or in part,
prior to the Maturity Date without the prior written consent of Genzyme.  All
principal payments hereunder shall be in immediately available funds and
accompanied by payment of all accrued interest on the amount repaid to the date
of repayment.  In case any payment date for principal or interest falls on a
Saturday, Sunday or holiday, payment shall be made on the preceding business
day.

 At the Additional Shares Closing (as such term is defined in the Stock Purchase
Agreement), upon fulfillment or waiver of the conditions set forth in Section 3
of the Stock Purchase Agreement, Genzyme shall surrender this Note to Aronex for
cancellation in exchange for certificates for the number of shares of Aronex
Common Stock to which Genzyme is entitled pursuant to the Advance Agreement.  If
so requested by Aronex, the Note surrendered for conversion shall be endorsed or
accompanied by written instrument or instruments of transfer, in form reasonably
satisfactory to Aronex, duly executed by an authorized officer of Genzyme or by
its attorney duly authorized in writing.

 PRESENTMENT, DEMAND, PROTEST AND NOTICE OF DISHONOR AND NON-PAYMENT ARE HEREBY
WAIVED BY THE UNDERSIGNED.
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 This Note shall be governed by the laws of the Commonwealth of Massachusetts
and shall have the effect of an instrument under seal as of the date first above
written.

                                         Aronex Pharmaceuticals, Inc.


                                         By:   /s/ James Chubb
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                                         Name:     James Chubb
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                                         Title:    President
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