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                                                                   EXHIBIT 10.12

            AMENDMENT TO ASSIGNMENT, ASSUMPTION AND LICENSE AGREEMENT

THIS AMENDMENT to the Assignment, Assumption and License Agreement dated as of
October 7, 1999 (the "Agreement") by and between IMARX, LLC, an Arizona limited
liability company ("Purchaser") and IMARX PHARMACEUTICAL CORP., an Arizona
corporation ("Seller") is entered into and effective this 31 day of July, 2000
by and between IMARX THERAPEUTICS, INC., successor in interest to Purchaser
("ImaRx") and DuPont Contrast Imaging, Inc. ("DuPont"), successor in interest to
Seller. Capitalized terms used but not otherwise defined herein have the
meanings assigned to them in the Agreement.

                                    RECITALS

         A. Purchaser and Seller entered into the Agreement as of October 7,
1999. Thereafter, Seller was merged into DuPont.

         B. Exhibit A and Exhibit B to the Agreement were incomplete. The
parties now wish to correct this error by amending Exhibit A and Exhibit B to
conform to the parties' original understanding.

         NOW, THEREFORE, in consideration of the foregoing premises and of the
agreements and covenants set forth in the Agreement, the parties agree as
follows:

                                    AGREEMENT

1.       Assignment of Assets. Attached hereto is Exhibit E. Exhibit E sets
         forth additional Category III Assets that were intended to be and
         hereby are included in Exhibit A, effective as of the date of the
         Agreement. DuPont will execute any other or further documents
         reasonably deemed necessary to reflect the transfer of the assets set
         forth in Exhibit E to ImaRx in accordance with the terms of the
         Agreement.

2.       License of Assets. Attached hereto is Exhibit F. Exhibit F sets forth
         additional Category II Assets that were intended to be and hereby are
         included in Exhibit B, effective as of the date of the Agreement. The
         Assets set forth in Exhibit F are subject to the license terms of
         Paragraph 4 of the Agreement, effective as of the date of the
         Agreement.

3.       No Warranty. DuPont believes that it has not assigned, conveyed,
         licensed or otherwise transferred any interest in any asset listed on
         Exhibit E to any other person or entity. DuPont believes that it has
         not licensed or otherwise transferred any interest in any asset listed
         on Exhibit F that would conflict with or be contrary to the exclusive
         license to ImaRx as provided in Paragraph 4 of the Agreement.
         Notwithstanding anything to the contrary, DuPont makes no warranty,
         express or implied, regarding the assets listed on Exhibit E and
         specifically disclaims any responsibility for any action or inaction
         with respect to the assets, including action or inaction with regard to
         the prosecution of any patents or any other protection of any
         intellectual property embodied or reflected in Exhibit E and Exhibit F
         during the period from the date of the Agreement to the date of this
         Amendment.

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4.       Continued Effect. Except as amended hereby, the Agreement remains in
         full force and effect.

IN WITNESS WHEREOF, the parties hereto have caused this Agreement to be duly
executed as of 31 the day and year first above written.

DUPONT CONTRAST IMAGING INC,            IMARX THERAPEUTICS, INC.,
a Delaware general partnership          an Arizona corporation


By:  /s/ Nicholas L. Teti               By:   /s/ Evan C. Unger
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      Nicholas L. Teti                        Dr. Evan Unger
Its:                                    Its:  President
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