EPIX Medical, Inc. has omitted from this Exhibit 10.42 portions of the
agreement for which EPIX Medical, Inc. has requested confidential treatment from
the Securities and Exchange Commission. The portions of the agreement for which
confidential treatment has been requested are marked [*] and such confidential
portions have been filed separately with the Securities and Exchange Commission.



                                 AMENDMENT NO. 1

         This Amendment No. 1 dated as of September 10, 1998, is made by and
among EPIX MEDICAL, INC., a Delaware corporation having its principal place of
business at 71 Rogers Street, Cambridge, Massachusetts 02142-1118 U.S.A.
("Epix"), MALLINCKRODT MEDICAL, INC., a Delaware corporation having its
principal place of business at 675 McDonnell Boulevard, St. Louis, Missouri
63134, and MALLINCKRODT INC., (under its prior corporate name MALLINCKRODT GROUP
INC.) a New York corporation having its principal place of business at 7733
Forsyth Boulevard, St. Louis, Missouri 63105, by and through its unincorporated
Medical Imaging division (together with Mallinckrodt Medical, Inc., "MKG").

                                    RECITALS

         WHEREAS, Epix (under its prior corporate name Metasyn, Inc.) and MKG
are parties to a Strategic Collaboration Agreement dated as of August 30, 1996
(the "Collaboration Agreement"); and

         WHEREAS, Epix and MKG desire to amend the Collaboration Agreement to
clarify the rights and obligations of the parties with respect to certain third
party arrangements, as set forth herein.

         NOW THEREFORE, in consideration of the premises Epix and MKG mutually
agree as follows:

                              ARTICLE I. AMENDMENT

1. Epix and MKG hereby agree to amend Article 4 of the Collaboration Agreement
by adding the following new Section 4.8:

         4.8      Collaboration Agreements with Third Parties:

                  4.8.1 General. In the event that either Party, during the term
                  of the Development Phase or thereafter, determines that a
                  research, development or collaboration agreement with a Third
                  Party would further the objectives of this Agreement (a "Third
                  Party Collaboration"), such Party (the "Collaborating Party")
                  shall so notify the Joint Steering Committee, which notice
                  shall include reasonable details concerning the terms of the
                  proposed Third Party Collaboration, including its objectives,
                  term, proposed budget, and the manner in which intellectual
                  property rights arising therefrom are to be made available to
                  the Collaborating Party. The Joint Steering Committee shall
                  make a determination as soon as practicable after such notice,
                  but in no event later than ninety (90) days thereafter, as to
                  whether to approve the proposed Third Party Collaboration,


                                   Page 1 of 6
September 10, 1998
<PAGE>

                  and to treat the costs of the Third Party Agreement (as
                  defined below) as Development Costs to be borne equally by the
                  parties hereunder.

                  4.8.2. Amendment to Development Plan and Budget. Upon approval
                  by the Joint Steering Committee of a Third Party
                  Collaboration, the current Development Plan and Budget will be
                  amended to reflect the additional anticipated costs of the
                  Third Party Agreement, and the Parties will share the costs
                  thereof as provided in Section 8.3.

                  4.8.3. Approval of Agreement and Any Amendments. Following
                  approval by the Joint Steering Committee of a Third Party
                  Collaboration, the Collaborating Party will proceed to
                  negotiate the definitive terms thereof, keeping the other
                  Party reasonably informed, will consider in good faith any
                  comments or suggestions of the other Party relating thereto,
                  and shall in any event obtain the written approval of the
                  other Party prior to executing the definitive agreement (the
                  "Third Party Agreement") or any material amendments thereto.

                  4.8.4. Sharing of Developments and Information. Following
                  execution of a Third Party Agreement as provided in Section
                  4.8.3, the Collaborating Party agrees, subject to the
                  confidentiality provisions hereof, to keep the other Party
                  regularly informed of all material developments under the
                  Third Party Agreement, including all reports, technical
                  information and data, and intellectual property rights arising
                  therefrom. Upon request of the other Party, to the extent
                  reasonably feasible, and subject in appropriate circumstances
                  to the other Party entering into agreements to be bound by
                  applicable terms of the Third Party Agreement, the
                  Collaborating Party will permit representatives of the other
                  Party to attend and participate in meetings with
                  representatives of the Third Party conducting the
                  collaboration.

                  4.8.5. Sharing of Intellectual Property Rights. The
                  Collaborating Party under any Third Party Agreement agrees
                  that the other Party will have a joint undivided interest in
                  any patent rights or other intellectual property rights
                  obtained by the Collaborating Party as a result of any Third
                  Party Agreement, and, upon request of the other Party, the
                  Collaborating Party agrees to execute and deliver to the other
                  Party any documents of assignment necessary to effect the
                  foregoing. Except as otherwise agreed, the Collaborating Party
                  will be responsible, in consultation with the other Party, for
                  the preparation, filing, prosecution and maintenance of any
                  patent applications or patents, the costs of which shall be
                  Development Costs to be shared by the Parties under Section
                  8.3.

                  4.8.6. Existing and Proposed Third Party Collaborations. The
                  Parties acknowledge that [*], Epix's agreement with the
                  General Electric Company ("GEC") dated as of January 9,
                  1998,


[*] Omitted portions filed separately with the Securities and Exchange
    Commission.


                                   Page 2 of 6
September 10, 1998
<PAGE>

                  [*] are approved Third Party Agreements hereunder. [*] has not
                  yet been the subject of a formal notice pursuant to Section
                  4.8.1 above.

                  4.8.7. Failure to Accept a Third Party Collaboration. If the
                  Joint Steering Committee declines to approve a proposed Third
                  Party Collaboration under Section 4.8.1, the Collaborating
                  Party shall have the right to enter into the Third Party
                  Agreement at its own expense, and the other Party shall have
                  no right to any intellectual property or other rights arising
                  from such Third Party Agreement, except as otherwise provided
                  in this Agreement.

2. Epix and MKG hereby agree to amend Article 5 of the Collaboration Agreement
so that the following Sections are amended and restated, or added, to read in
their entirety as follows:

                  5.1. Additional Research Programs. In the event that either
                  Party, during the term of this Agreement, has what it believes
                  is a valid concept for discovering potential Second Generation
                  Compounds that are reasonably likely to have successful
                  commercial application, such Party shall promptly report such
                  concept to the Joint Steering Committee together with a
                  recommended specific research program pursuant to which any
                  such concept could be added to the Program. Such
                  recommendation shall include a proposed research plan and
                  budget and shall include details explaining why the
                  recommending party believes that the proposed concept could
                  lead to the discovery of Second Generation Compounds that may
                  have significant performance or other advantages over the
                  compounds ongoing Research Programs. The Joint Steering
                  Committee shall make a determination with respect to each such
                  recommendation as soon as practicable after such
                  recommendation is made but in no event later than ninety (90)
                  days. In the event that the Joint Steering Committee fails or
                  declines to approve any recommended research program as an
                  addition to the Program within the aforementioned ninety (90)
                  day period (or such longer period as the Parties may mutually
                  agree), then the Party which recommended such research program
                  shall be free to develop, market and sell any compounds
                  developed in such research program by itself, including with
                  the assistance of third party contractors, provided, however,
                  that any compounds developed in such research program [*].

                  If the Joint Steering Committee approves the recommended
                  research program as an addition to the Program, then the
                  research program may commence immediately in


[*] Omitted portions filed separately with the Securities and Exchange
    Commission.

                                   Page 3 of 6
September 10, 1998
<PAGE>

                  accordance with the proposed research plan and budget. At such
                  time during the research program as either Party identifies a
                  specific potential Second Generation Compound for development,
                  such Party shall promptly report such compound to the Joint
                  Steering Committee together with a recommended specific
                  research plan and budget relating to the development of such
                  compound. The Joint Steering Committee shall make a
                  determination with respect to each such recommendation as soon
                  as practicable after such recommendation is made but in no
                  event later than ninety (90 days). If the Joint Steering
                  Committee approves the recommended research program for the
                  specific potential Second Generation Compound as an addition
                  to the Program, then the research program for such compound
                  may commence immediately in accordance with the proposed
                  research plan and budget. In the event that the Joint Steering
                  Committee fails or declines to approve any recommended
                  research program for the specific potential Second Generation
                  Compound as an addition to the Program within the
                  aforementioned ninety (90) day period (or such longer period
                  as the Parties may mutually agree) then the non-recommending
                  Party shall either [*].

                  5.1.1. Ongoing Research Programs. Epix and MKG acknowledge
                  that they are currently engaged in a single Research Program
                  under the Collaboration Agreement which relates to albumin
                  binding for second generation intravascular contrast agents,
                  which Research


[*] Omitted portions filed separately with the Securities and Exchange
    Commission.

                                   Page 4 of 6
September 10, 1998
<PAGE>

                  Program is more fully described in correspondence between
                  Epix and MKG dated [*]. Unless otherwise agreed by Epix and
                  MKG, Epix and MKG agree that there shall be no more than [*]
                  Research Programs being conducted at any time. Unless
                  otherwise agreed by Epix and MKG, should a research program
                  concept be proposed and the Joint Steering Committee
                  recommend that such concept could be added to the Program
                  while [*] Research Programs are being conducted, any such
                  recommended Research Program shall be delayed until [*] the
                  ongoing Research Programs [*] been completed.

                  5.2.1. General. The Joint Steering Committee will determine
                  the allocation of responsibility between the Parties for the
                  conduct of each approved Research Program. Upon approval of a
                  Research Program, the Joint Steering Committee shall select a
                  Joint Scientific Team consisting of five (5) members, three
                  (3) from the recommending Party and two (2) from the
                  non-recommending Party, to direct the research. The Joint
                  Scientific Team shall issue a written progress report
                  quarterly and shall make an oral status presentation at each
                  meeting of the Joint Steering Committee. Each of the Parties
                  will attempt to achieve efficiently and expeditiously the
                  objectives assigned to it by the Joint Steering Committee as
                  described in the Annual Research Plan (defined below) and will
                  proceed diligently with the work described therein by using
                  its good faith efforts. The Joint Steering Committee shall
                  have the authority to mandate changes in the direction of the
                  Research Program or to mandate its discontinuance at any time.

3. Epix and MKG hereby agree to amend Article 8 of the Collaboration Agreement
so that the following section is amended and restated to read in its entirety as
follows:

                  8.3.5. Notwithstanding any other provision hereof, it is
                  understood that, without its prior written consent, neither
                  Party shall be liable to pay an amount in Development Costs
                  hereunder with respect to the Licensed Compound and any
                  Replacement Compounds and their corresponding Licensed
                  Products of more than [*].

4. Epix and MKG hereby agree to amend Article 13 of the Collaboration Agreement
so that the following section is amended and restated to read in its entirety as
follows:

                  13.2.4. Effect of Termination of the Research Program. In the
                  event that the Research Program is terminated with respect to
                  any compound pursuant to Section 13.2.2, then such compound
                  may not be designated as a Second Generation Compound or a
                  Replacement Compound by the Joint Steering Committee and
                  neither party, alone or with a Third Party, shall have the
                  right to develop a product for sale in the Field based upon
                  such compound; provided, however, that if the compound
                  demonstrates [*]


[*] Omitted portions filed separately with the Securities and Exchange
    Commission.



                                   Page 5 of 6
September 10, 1998
<PAGE>

                  over any compound then in research or development or
                  being marketed or sold under the collaboration, then, in such
                  event, (a) all rights with respect to the use, manufacture,
                  distribution for sale and sale of such compound shall revert
                  to the Originating Party, except that, to the extent such
                  compound has been jointly acquired through license, purchase
                  or otherwise, both Parties will have the right to use,
                  manufacture, distribute for sale and sell such compound on a
                  nonexclusive basis, (b) to the extent legally permissible, all
                  additional action reasonably necessary shall be taken by the
                  Parties to assign all right, title and interest in and
                  transfer possession and control of the regulatory filings and
                  regulatory approvals relating to such compound and (c) the
                  Originating Party shall be free to develop or grant licenses
                  to Third Parties with respect to such compound. In the event
                  that the Originating Party enters into an agreement with a
                  Third Party pursuant to clause (c) hereof and such Third Party
                  will use data generated during the Program, then the
                  Originating Party shall provide in such agreement that such
                  Third Party shall reimburse the non-Originating Party for the
                  perceived value of such data, such value to be negotiated in
                  good faith by MKG and Metasyn taking into account the
                  financial contributions of both Parties to the generation of
                  such data.

                            ARTICLE 2 - MISCELLANEOUS

     Except as expressly amended by this Amendment No. 1, the Collaboration
Agreement shall remain unmodified and in full force and effect. This Amendment
No. 1 may be executed in two or more counterparts, each of which shall be deemed
an original, but all of which together shall constitute one and the same
instrument. This Amendment No. 1 shall be governed and construed in accordance
with the laws of the State of New York without giving effect to the choice of
law provisions thereof.

     IN WITNESS WHEREOF, the Parties have executed this Amendment No. 1 as of
the date set forth above.

<TABLE>
     <S>                                     <C>
     EPIX MEDICAL, INC.                      MALLINCKRODT INC.

     By: /s/ Michael D. Webb                 By: /s/ James C. Carlile
     -----------------------                 ------------------------
     Name:   Michael D. Webb                 Name:   James C. Carlile
     Title:  President and Chief             Title:  President, Imaging Group
             Executive Officer
</TABLE>


[*] Omitted portions filed separately with the Securities and Exchange
    Commission.


                                   Page 6 of 6
September 10, 1998