<PAGE>

                                                               Exhibit 10.15

                                  CONFIDENTIAL TREATMENT HAS BEEN SOUGHT FOR
                             PORTIONS OF THIS EXHIBIT PURSUANT TO RULE 24B-2
                       UNDER THE SECURITIES EXCHANGE ACT OF 1934, AS AMENDED


                                                              EXECUTION COPY


             SUBSCRIPTION, JOINT DEVELOPMENT AND OPERATING AGREEMENT


                        ELAN PHARMA INTERNATIONAL LIMITED


                        ELAN INTERNATIONAL SERVICES, LTD.


                                       AND


                           PHOTOGEN TECHNOLOGIES, INC.


                                       AND


                               PHOTOGEN NEWCO LTD.

<PAGE>


                                      INDEX
                                      -----

<TABLE>
<S>         <C>
CLAUSE 1    DEFINITIONS

CLAUSE 2    BUSINESS

CLAUSE 3    REPRESENTATIONS AND WARRANTIES

CLAUSE 4    AUTHORIZATION AND CLOSING

CLAUSE 5    DIRECTORS; MANAGEMENT AND R&D COMMITTEES

CLAUSE 6    THE BUSINESS PLAN AND REVIEWS

CLAUSE 7    RESEARCH AND DEVELOPMENT

CLAUSE 8    COMMERCIALIZATION

CLAUSE 9    SUBLICENSE AND ASSIGNMENT RIGHTS

CLAUSE 10   OWNERSHIP OF INTELLECTUAL PROPERTY RIGHTS/[****]

CLAUSE 11   INTELLECTUAL PROPERTY RIGHTS

CLAUSE 12   CROSS LICENSING/EXPLOITATION OF PRODUCTS OUTSIDE FIELD

CLAUSE 13   REGULATORY

CLAUSE 14   MANUFACTURING

CLAUSE 15   TECHNICAL SERVICES AND ASSISTANCE
</TABLE>
----------------

[****]   REPRESENTS MATERIAL WHICH HAS BEEN REDACTED PURSUANT TO A REQUEST
         FOR CONFIDENTIAL TREATMENT PURSUANT TO RULE 24B-2 UNDER THE
         SECURITIES EXCHANGE ACT OF 1934, AS AMENDED.

<PAGE>

<TABLE>
<S>         <S>
CLAUSE 16   AUDITORS, BANKERS, REGISTERED OFFICE,
            ACCOUNTING REFERENCE DATE; SECRETARY; COUNSEL

CLAUSE 17   TRANSFER OF SHARES; RIGHTS OF FIRST OFFER; TAG ALONG RIGHTS

CLAUSE 18   MATTERS REQUIRING PARTICIPANTS' APPROVAL

CLAUSE 19   DISPUTES

CLAUSE 20   TERMINATION

CLAUSE 21   SHARE RIGHTS

CLAUSE 22   CONFIDENTIALITY

CLAUSE 23   COSTS

CLAUSE 24   GENERAL
</TABLE>

<PAGE>

THIS SUBSCRIPTION, JOINT DEVELOPMENT AND OPERATING AGREEMENT made this 20th
day of October, 1999

BETWEEN:

(1)      ELAN PHARMA INTERNATIONAL LIMITED, a public limited company
         incorporated under the laws of Ireland, and having its registered
         office at WIL House, Shannon Business Park, Shannon, County Clare,
         Ireland ("EPIL");

(2)      ELAN INTERNATIONAL SERVICES, LTD., an exempted limited liability
         company incorporated under the laws of Bermuda, and having its
         registered office at Clarendon House, 2 Church St., Hamilton, Bermuda
         ("EIS");

(3)      PHOTOGEN TECHNOLOGIES, INC. a corporation duly incorporated and
         validly existing under the laws of Nevada and having its principal
         place of business at 7327 Oak Ridge, Knoxville, TN. 37931, United
         States of America ("Photogen"); and

(4)      PHOTOGEN NEWCO LTD. an exempted limited liability company incorporated
         under the laws of Bermuda, and having its registered office at
         Clarendon House, 2 Church St., Hamilton, Bermuda ("NEWCO").

RECITALS:

A.       Newco desires to issue and sell to Photogen and Photogen desires to
         purchase from Newco, for aggregate consideration of $12,015,000, 12,000
         ordinary shares of Newco's common stock, par value $1.00 per share (the
         "COMMON STOCK"). Additionally, Newco desires to issue and sell to EIS
         and EIS desires to purchase from Newco, for aggregate consideration of
         $2,985,000, 2,980 shares of Newco's non-voting convertible preferred
         stock, par value $1.00 per share (the "PREFERRED STOCK").

B.       As of the date hereof, EPIL has entered into a license agreement with
         Newco, and Photogen has entered into a license agreement with Newco, in
         connection with the license to Newco of the Elan Intellectual Property
         and the Photogen Intellectual Property, respectively (each as defined
         below).

<PAGE>

C.       Elan and Photogen have agreed to co-operate in the research,
         development and commercialization of the Products (as defined below)
         based on their respective technologies.

D.       Elan and Photogen have agreed to enter into this Agreement for the
         purpose of recording the terms and conditions regulating their
         relationship with each other, with respect to the Licensed Technologies
         and with Newco.

NOW IT IS HEREBY AGREED AS FOLLOWS:

                                    CLAUSE 1

                                   DEFINITIONS

1.1      In this Agreement, the following terms shall, where not
         inconsistent with the context, have the following meanings
         respectively.

         "AFFILIATE" shall mean any corporation or entity controlling,
         controlled or under the common control of Elan or Photogen, as the case
         may be. For the purpose of this definition, "control" shall mean direct
         or indirect ownership of fifty percent (50%) or more of the stock or
         shares entitled to vote for the election of directors. Newco is not an
         Affiliate of Elan or EIS.

         "AGREEMENT" shall mean this agreement (which expression shall be deemed
         to include the Recitals and the Schedules hereto).

         "ALLIANCE" shall mean Alliance Pharmaceutical Corp., whose principal
         place of business is at 3040 Science Park Road, San Diego, California.

         "ALLIANCE AGREEMENT" shall mean the Agreement dated 9 August 1999,
         between Alliance, Photogen and Dr. Gerald Wolf ("DR WOLF"), which
         agreement, inter alia, assigned the Method Patents from Alliance and
         Dr. Wolf to Photogen.

         "BOARD" shall mean the board of directors of Newco.

         "BUSINESS" shall mean the business specified in the Business Plan.

         "BUSINESS PLAN" shall mean the business plan and program of development
         to be agreed by Elan and Photogen pursuant to Clause 6, that shall
         contain, among other things, to the extent practicable, the research
         and development objectives, desired Product specifications, clinical
         indications, preliminary clinical trial designs (Phase I/II),
         development timelines, budgeted costs and the relative responsibilities
         of Photogen and Elan as it relates to the implementation of the

<PAGE>

         R&D Plan.

         "CERTIFICATE OF DESIGNATIONS" shall mean that certain certificate of
         designations, preferences and rights of Series A Preferred Stock of
         Photogen issued on the date hereof.

         "CLOSING DATE" shall mean the date upon which the Transaction Documents
         are executed and delivered by the Parties and the transactions effected
         thereby are closed.

         "COMMON STOCK EQUIVALENTS" shall mean any options, warrants, rights or
         any other securities convertible, exercisable or exchangeable, in whole
         or in part, for or into Common Stock.

         "COMPOUNDS" shall mean the diagnostic imaging agents compounds [****].

         "CONTROL" shall mean the ability to grant a license or sublicense as
         contemplated herein without violating the terms of any agreement with
         any third party.

         "DIRECTORS" shall mean, at any time, the directors of Newco.

         "EIS DIRECTOR" has the meaning set forth in Clause 5.

         "ELAN" shall mean EPIL (a wholly owned subsidiary of Elan Corporation,
         plc., which owns the Nanocrystal-TM- technology formerly controlled by
         NanoSystems LLC, formerly a subsidiary of the Eastman Kodak Company)
         and Affiliates and subsidiaries of Elan Corporation, plc. within the
         division of Elan Corporation, plc. carrying on business as Elan
         Pharmaceutical Technologies ("EPT") but shall not include Affiliates
         and subsidiaries (present or future) of Elan Corporation plc. within
         the division of Elan Corporation, Plc carrying on business as Elan
         Pharmaceuticals which incorporates, inter alia, Targon Corporation,
         Athena Neurosciences, Inc., Elan Pharmaceuticals, Inc., Elan
         Diagnostics, Carnrick Laboratories, and Elan Europe Limited.

----------------

[****]   REPRESENTS MATERIAL WHICH HAS BEEN REDACTED PURSUANT TO A REQUEST
         FOR CONFIDENTIAL TREATMENT PURSUANT TO RULE 24B-2 UNDER THE
         SECURITIES EXCHANGE ACT OF 1934, AS AMENDED.

<PAGE>


         "ELAN IMPROVEMENTS" shall mean improvements relating to the Elan
         Patents and/or the Elan Know-How , developed (i) by Elan not pursuant
         to the Project, (ii) by Elan pursuant to the Project except for that
         portion of improvements relating solely and specifically to Product(s)
         (iii) by Newco or Photogen or by a third party (under contract with
         Newco) pursuant to the Project except for that portion of improvements
         relating solely and specifically to Product(s), and/or (iv) jointly by
         any combination of Elan, Photogen or Newco pursuant to the Project
         except for that portion of improvements relating solely and
         specifically to Product(s), except as limited by agreements with
         unaffiliated third parties.

         Subject to third party agreements with unaffiliated third parties, Elan
         Improvements shall constitute part of Elan Intellectual Property and be
         included in the license of the Elan Intellectual Property pursuant to
         Clause 3.1 solely for the purposes set forth therein. If the inclusion
         of a Elan Improvement in the license of Elan Intellectual Property is
         restricted or limited by a third party agreement, Elan shall use
         reasonable commercial efforts to minimize any such restriction or
         limitation.

         "ELAN INTELLECTUAL PROPERTY" shall mean the Elan Know-How, the Elan
         Patents and the Elan Improvements.

         For the avoidance of doubt, Elan Intellectual Property shall exclude
         (i) Elan's patent rights and know-how relating to drug delivery devices
         including parenteral administration of a diagnostic imaging agent via a
         drug delivery device such as Medipad and (ii) inventions, patents and
         know-how owned, licensed or Controlled by Axogen Limited and Neuralab
         Limited, and by all Affiliates and subsidiaries (present or future) of
         Elan Corporation, plc. within the division of Elan Corporation, plc.
         carrying on business as Elan Pharmaceuticals which incorporates, inter
         alia, Targon Corporation, Athena Neurosciences, Inc., Elan
         Pharmaceuticals, Inc., Elan Diagnostics, Carnrick Laboratories, and
         Elan Europe Limited.

         "ELAN KNOW-HOW" shall mean any and all rights owned, or Controlled by
         Elan to any Know-How relating to nanoparticulate medical diagnostic
         imaging agents including, without limitation, [****]

         The primary examples of the Elan Know-How existing as of the date
         hereof are set forth on Schedule 1 of the Elan License Agreement, which
         listing is not necessarily exhaustive.
----------------

[****]   REPRESENTS MATERIAL WHICH HAS BEEN REDACTED PURSUANT TO A REQUEST
         FOR CONFIDENTIAL TREATMENT PURSUANT TO RULE 24B-2 UNDER THE
         SECURITIES EXCHANGE ACT OF 1934, AS AMENDED.

         "ELAN LICENSE AGREEMENT" shall mean the license agreement between Elan
         and

<PAGE>

         Newco, of even date herewith, attached hereto in Schedule 1.

         "ELAN PATENTS" shall mean any and all Patent Rights owned or Controlled
         by Elan, now existing, currently pending or hereafter filed by Elan
         relating to nanoparticulate medical diagnostic imaging agents
         including, without limitation, [****]. Representative Elan Patents
         existing as of the date hereof are set forth in Schedule 1 of the Elan
         License Agreement.

         "ENCUMBRANCE" shall mean any liens, charges, encumbrances, equities,
         claims, options, proxies, pledges, security interests, or other similar
         rights of any nature.

         "EXCHANGE ACT" shall mean the Securities Exchange Act of 1934, as
         amended.

         "EXCHANGE RIGHT" has the meaning assigned to such term in Section 5.a
         of the Certificate of Designations in effect on the date hereof.

         "FIELD" shall mean the research, development, manufacture and
         commercialization of nanoparticulate x-ray, CT, and/or MRI diagnostic
         imaging agents using radio-opaque molecules containing Iodine that
         passively target to lymphnodes involved in a disease state following
         parenteral administration to a mammal to locate, diagnose and/or treat
         cancer and/or other diseases.

         For the avoidance of doubt, the Field does not include:

         (1)      active targeting agents, including but not limited to
                  monoclonal antibodies, short-chain antibodies or any other
                  active targeting agents including protein, peptide or
                  peptidomimetic targeting agents; or

         (2)      ultrasound diagnostic imaging agents.

         "FINANCIAL YEAR" shall mean each year commencing on January 1 (or in
         the case of the first Financial Year, the date hereof) and expiring on
         December 31 of each year.

         "FULLY DILUTED COMMON STOCK" shall mean all of the issued and
         outstanding Common Stock, assuming the conversion, exercise or exchange
         of all outstanding Common Stock Equivalents.

----------------

[****]   REPRESENTS MATERIAL WHICH HAS BEEN REDACTED PURSUANT TO A REQUEST
         FOR CONFIDENTIAL TREATMENT PURSUANT TO RULE 24B-2

<PAGE>


         UNDER THE SECURITIES EXCHANGE ACT OF 1934, AS AMENDED

         "FUNDING AGREEMENT" shall mean the Funding Agreement, dated as of the
         date hereof, among EIS, Elan and Photogen.

         "GENERAL NYCOMED AGREEMENT" shall mean the License Agreement between
         The General Hospital Corporation (acting, inter alia, as agent for
         Nycomed) and Photogen which agreement sublicenses or licenses, as
         applicable, inter alia, certain rights with respect to the Compounds
         [****] and [****] to Photogen.

         "GENERAL NYCOMED PATENTS" shall mean the patents included in the GenNyc
         Intellectual Property.

         "GENNYC INTELLECTUAL PROPERTY" shall mean all the rights to and under
         the General Patent Rights, the Joint Patent Rights and the [****]
         Patent Rights (as those terms are defined in the General Nycomed
         Agreement) which are licensed or sublicensed as applicable to Photogen
         pursuant to the General Nycomed Agreement.

         The primary examples of GenNyc Intellectual Property existing as of the
         date hereof are set forth on Schedule 2 of the Photogen License
         Agreement, which listing is not necessarily exhaustive.

         "KNOW-HOW" shall mean information and know-how, whether patentable or
         not, including but not limited to any and all discoveries, inventions,
         substances, data, techniques, processes, systems, formulations, designs
         and commercial information relating to design, development,
         manufacture, assembly, use or sale.

         "LICENSE AGREEMENTS" shall mean the Elan License Agreement and the
         Photogen License Agreement.

         "LICENSED  TECHNOLOGIES" shall mean the Elan Intellectual  Property,
         the Photogen Intellectual Property and the GenNyc Intellectual
         Property.

         "METHOD PATENTS" shall mean the patent family that contains the [****]
         Patent, the [****] Patent, [****] and others as described in Exhibit B
         of the Alliance Agreement.

----------------

[****]   REPRESENTS MATERIAL WHICH HAS BEEN REDACTED PURSUANT TO A REQUEST
         FOR CONFIDENTIAL TREATMENT PURSUANT TO RULE 24B-2 UNDER THE
         SECURITIES EXCHANGE ACT OF 1934, AS AMENDED.

<PAGE>

         "NEWCO INTELLECTUAL PROPERTY" shall mean all Patent Rights and Know-How
         and other intellectual property arising pursuant to the Project by any
         person, that does not constitute Elan Intellectual Property or Photogen
         Intellectual Property and any technology licensed or acquired by Newco
         from a third party.

         For avoidance of doubt, Newco Intellectual Property includes all
         improvements developed pursuant to the Project and relating solely and
         specifically to Product(s).

         "NEWCO MEMORANDUM OF ASSOCIATION AND BYE-LAWS" shall mean the
         Memorandum of Association and Bye-Laws of Newco.

         "NEWCO PATENTS" shall mean any and all Patent Rights now existing,
         currently pending or hereafter filed or obtained relating to the Newco.

         "NOTE" shall mean that certain convertible promissory note, of even
         date herewith, by and between Photogen and EIS.

         "NYCOMED" shall mean Nycomed Imaging AS doing business as Nycomed
         Amersham, whose principal place of business is at 101 Carnegie Center,
         Princeton, NJ 08540, USA.

         "PARTICIPANT" shall mean Photogen or Elan, as the case may be, and
         "PARTICIPANTS" shall mean both of the Participants together as the
         context requires;

         "PARTY" shall mean Elan, Photogen, or Newco, as the case may be, and
         "PARTIES" shall mean all three together.

         "PATENT RIGHTS" shall mean any and all patents and patent applications,
         including all divisionals, continuations, continuations-in-part,
         extensions, patents-of-additions, re-examinations, re-issues,
         supplementary protection certificates and foreign counterparts of such
         patents and patent applications and any patents issuing thereon and
         extensions thereon.

         "PERMITTED TRANSFEREE" shall mean any Affiliate or subsidiary of Elan,
         EIS or Photogen, to whom this Agreement may be assigned, in whole or in
         part, pursuant to the terms hereof or in the case of Elan/EIS, a
         special purpose financing or similar vehicle created by Elan or EIS.

         "PERSON" shall mean an individual, partnership, corporation, limited
         liability company, business trust, joint stock company, trust,
         unincorporated association, joint venture, governmental entity or
         authority or other entity of whatever nature.

<PAGE>

         "PHOTOGEN" shall mean Photogen and its Affiliates, excluding Newco.

         "PHOTOGEN DIRECTORS" has the meaning set forth in Clause 5.

         "PHOTOGEN IMPROVEMENTS" shall mean improvements relating to the
         Photogen Patents and/or the Photogen Know-How, developed (i) by
         Photogen not pursuant to the Project, (ii) by Photogen pursuant to the
         Project except for that portion of improvements relating solely and
         specifically to Product(s) (iii) by Newco or Elan or by a third party
         (under contract with Newco) pursuant to the Project except for that
         portion of improvements relating solely and specifically to Product(s),
         and/or (iv) jointly by any combination of Photogen, Elan or Newco
         pursuant to the Project except for that portion of improvements
         relating solely and specifically to Product(s), except as limited by
         agreements with unaffiliated third parties.

         Subject to third party agreements with unaffiliated third parties,
         Photogen Improvements shall constitute part of Photogen Intellectual
         Property and be included in the license of the Photogen Intellectual
         Property pursuant to Clause 4.1 solely for the purposes set forth
         therein. If the inclusion of a Photogen Improvement in the license of
         Photogen Intellectual Property is restricted or limited by a third
         party agreement, Photogen shall use reasonable commercial efforts to
         minimize any such restriction or limitation.

         "PHOTOGEN  INTELLECTUAL  PROPERTY" shall mean the Photogen Know-How,
          the Photogen Patents and the Photogen Improvements.

         "PHOTOGEN KNOW-HOW" shall mean any and all rights owned, licensed or
         Controlled by Photogen to Know-How, relating to medical diagnostic
         imaging agents, methods of treatment using medical diagnostic imaging
         agents and related compositions.

         The primary examples of the Photogen Know-How existing as of the date
         hereof are set forth on Schedule 1 of the Photogen License Agreement,
         which listing is not necessarily exhaustive, and includes Know-How
         owned, licensed or Controlled by Photogen related to the Method
         Patents.

         "PHOTOGEN LICENSE AGREEMENT" shall mean the license agreement between
         Photogen and Newco, of even date herewith, attached hereto in Schedule
         2.

         "PHOTOGEN PATENTS" shall mean any and all Patent Rights owned or
         Controlled by Photogen other than Patent Rights included in the GenNyc
         Intellectual Property, now existing, currently pending or hereafter
         filed by Photogen relating to

<PAGE>

         nanoparticulate medical diagnostic imaging agents including medical
         diagnostic imaging agents, methods of treatment using medical
         diagnostic imaging agents and related compositions.

         The primary examples of Photogen Patents existing as of the date hereof
         are set forth on Schedule 1 of the Photogen License Agreement, which
         listing is not necessarily exhaustive, and includes the Method Patents.

         "PHOTOGEN SECURITIES PURCHASE AGREEMENT" shall mean that certain
         securities purchase agreement, of even date herewith, by and between
         Photogen and EIS.

         "PRODUCT" shall mean a formulation containing one or more x-ray, CT,
         and/or MRI Compounds in nanoparticulate form developed by or on behalf
         of Newco pursuant to the Project.

         "PROJECT" shall mean all activities as undertaken by Elan, Photogen and
         Newco in order to develop the Products.

         "R&D PLAN" shall mean the program of work, including the budget, agreed
         by the Management Committee as part of the Business Plan and such
         further research and development work as may be agreed by the
         Management Committee from time to time.

         "R&D PROGRAM" shall mean any research and development program
         commenced by Newco pursuant to the Project.

         "R&D TERM" shall mean the period commencing on the Closing Date and
         continuing for a period of [****] thereafter, or as extended by
         agreement of the Participants.

         "REGISTRATION RIGHTS AGREEMENTS" shall mean the Registration Rights
         Agreements of even date herewith relating to Newco and Photogen,
         respectively.

         "REGULATORY APPLICATION" shall mean any regulatory application or any
         other application for marketing approval for a Product, which Newco
         will file in any country of the Territory, including any supplements or
         amendments thereto.

         "REGULATORY APPROVAL" shall mean the final approval to market a Product
         in any country of the Territory, and any other approval which is
         required to launch the Product in the normal course of business.

----------------

[****]   REPRESENTS MATERIAL WHICH HAS BEEN REDACTED PURSUANT TO A REQUEST
         FOR CONFIDENTIAL TREATMENT PURSUANT TO RULE 24B-2

<PAGE>

         UNDER THE SECURITIES EXCHANGE ACT OF 1934, AS AMENDED

         "RHA" shall mean any relevant government health authority (or
         successor agency thereof) in any country of the Territory whose
         approval is necessary to market a Product in the relevant country of
         the Territory.

         [****]

         [****]

         "SECURITIES ACT" shall mean the Securities Act of 1933, as amended.

         "SHARES" shall mean the shares of Common Stock and shares of Preferred
         Stock of Newco.

         "STOCKHOLDER" shall mean any of EIS, Photogen, any Permitted Transferee
         or any other Person who subsequently becomes bound by this Agreement as
         a holder of the Shares, and "STOCKHOLDERS" shall mean all of the
         Stockholders together.

         "SUBSIDIARY" shall mean any company that is a subsidiary of Newco
         within the meaning of applicable laws.

         "TECHNOLOGICAL COMPETITOR OF ELAN" shall mean a company, corporation or
         person listed in Schedule 3 and successors thereof or any additional
         broad-based technological competitor of Elan added to such Schedule
         from time to time upon mutual agreement of the Parties.

         "TERM" shall mean the term of this Agreement.

         "TERRITORY" shall mean all of the countries of the world.

         "TRANSACTION DOCUMENTS" shall mean this Agreement, the Funding
         Agreement, Elan License Agreement, the Photogen License Agreement, the
         Note, the Warrant, the Photogen Securities Purchase Agreement, the
         Registration Rights Agreements, the Certificate of Designations and
         associated documentation of even date herewith, by and between
         Photogen, Elan, EIS and Newco, as applicable.

         "UNITED STATES DOLLAR" and "US$" and "$" shall mean the lawful
         currency of the United States of America.

         [****]

<PAGE>

----------------

[****]   REPRESENTS MATERIAL WHICH HAS BEEN REDACTED PURSUANT TO A REQUEST
         FOR CONFIDENTIAL TREATMENT PURSUANT TO RULE 24B-2 UNDER THE
         SECURITIES EXCHANGE ACT OF 1934, AS AMENDED.

<PAGE>

[****]

1.2      In addition, the following definitions have the meanings in the
         Clauses corresponding thereto, as set forth below.

<TABLE>
<CAPTION>
         DEFINITION                                       CLAUSE
         <S>                                             <C>
         "AAA"                                            20.6
         "Buyout Option"                                  20.4
         "Closing"                                         4.3
         "Common Stock"                                  Recital A
         "Confidential Information"                       22.1
         "Co-sale Notice"                                 17.5
         "Junior Securities"                              21.1
         "Management Committee"                          5.2.1
         "Notice of Exercise"                             17.4
         "Notice of Intention"                            17.4
         "Offered Shares"                                 17.4
         "Offer Price"                                    17.4
         "Preferred Stock"                               Recital A
         "Proposing Participant"                          20.4
         "Proposing Participant Price:                    20.6
         "Purchase Price"                                 20.6
         "R&D Committee"                                 5.2.2
         "Recipient Participant"                          20.4
         "Recipient Participant Price"                    20.6
         "Remaining Stockholders"                         17.5
         "Relevant Event"                                 20.2
         "Selling Stockholder"                            17.4
         "Tag-Along Right"                                17.5
         "Transaction Proposal"                           17.4
         "Transfer"                                       17.1
         "Transferee Terms"                               17.5
         "Transferring Stockholder"                       17.5
</TABLE>

1.3      Words importing the singular shall include the plural and vice versa.

1.4      Unless the context otherwise requires, reference to a recital,
         article, paragraph, provision, clause or schedule is to a recital,
         article, paragraph, provision, clause or schedule of or to this
         Agreement.

1.5      Reference to a statute or statutory provision includes a reference to
         it as from time to time amended, extended or re-enacted.

<PAGE>

1.6      The headings in this Agreement are inserted for convenience only and
         do not affect its construction.

1.7      Unless the context or subject otherwise requires, references to words
         in one gender include references to the other genders.

----------------

[****]   REPRESENTS MATERIAL WHICH HAS BEEN REDACTED PURSUANT TO A REQUEST
         FOR CONFIDENTIAL TREATMENT PURSUANT TO RULE 24B-2 UNDER THE
         SECURITIES EXCHANGE ACT OF 1934, AS AMENDED.

1.8      Capitalized terms used but not defined herein shall have the meanings
         ascribed in the Transaction Documents, if defined therein.

                                    CLAUSE 2

                                    BUSINESS

2.1      This Agreement shall regulate the business of the
         development, testing, registration, manufacture,
         commercialization and licensing of Products in the Territory
         and to achieve the other objectives set out in this Agreement.
         The focus of the Business will be to develop the Products using
         the Elan Intellectual Property, the Photogen Intellectual
         Property and the Newco Intellectual Property to agreed upon
         specifications and timelines.

2.2      The central management and control of Newco shall be exercised in
         Bermuda and shall be vested in the Directors and such Persons as they
         may delegate the exercise of their powers in accordance with the Newco
         Memorandum of Association and Bye-Laws. The Stockholders shall use
         their best endeavors to ensure that to the extent required pursuant to
         the laws of Bermuda, and to ensure the sole residence of Newco in
         Bermuda, all meetings of the Directors are held in Bermuda or other
         jurisdictions outside the United States and generally to ensure that
         Newco is treated as resident for taxation purposes in Bermuda.

2.3      Additional diagnostic imaging agent(s) may be selected from the
         Elan Intellectual Property or the Photogen Intellectual
         Property in the Field during the Term or from Newco
         Intellectual Property and designated as Compound(s) by the
         unanimous vote of the Management Committee. In such case, the
         Parties shall negotiate in good faith such amendments as are
         required to this Agreement, such as amending the provisions
         regulating non-competition.

<PAGE>

                                    CLAUSE 3

                         REPRESENTATIONS AND WARRANTIES

3.1      REPRESENTATIONS AND WARRANTIES OF NEWCO: Newco hereby represents and
         warrants to each of the Stockholders as follows, as of the date hereof:

         3.1.1    ORGANIZATION: Newco is an exempted company duly organized,
                  validly existing and in good standing under the laws of
                  Bermuda, and has all the requisite corporate power and
                  authority to own and lease its properties, to carry on its
                  business as presently conducted and as proposed to be
                  conducted.

         3.1.2    CAPITALIZATION: As of the date hereof, the authorized capital
                  stock of Newco consists of 12,000 shares of Common Stock and
                  12,000 shares of Preferred Stock. Prior to the date hereof, no
                  shares of capital stock of Newco have been issued.

         3.1.3    AUTHORIZATION:  The execution, delivery and performance by
                  Newco of this Agreement, including the issuance of the
                  Shares, have been duly authorized by all requisite
                  corporate actions; this Agreement has been duly executed
                  and delivered by Newco and is the valid and binding
                  obligation of Newco, enforceable against it in accordance
                  with its terms except as limited by applicable bankruptcy,
                  insolvency, reorganization,  moratorium and other laws of
                  general application affecting the enforcement of creditors'
                  rights generally, and except as enforcement of rights to
                  indemnity and contribution hereunder may be limited by
                  United States federal or state securities laws or
                  principles of public policy. The Shares, when issued as
                  contemplated hereby, will be validly issued and
                  outstanding, fully paid and non-assessable and not subject
                  to preemptive or any other similar rights of the
                  Stockholders or others.

         3.1.4    NO CONFLICTS: The execution, delivery and performance by Newco
                  of this Agreement, the issuance, sale and delivery of the
                  Shares, and compliance with the provisions hereof by Newco,
                  will not:

                  (i)      violate any provision of applicable law, statute,
                           rule or regulation applicable to Newco or any ruling,
                           writ, injunction, order, judgment or decree of any
                           court, arbitrator, administrative agency or other
                           governmental body applicable to Newco or any of its
                           properties or assets;

<PAGE>

                  (ii)    conflict with or result in any breach of any of the
                          terms, conditions or provisions of, or constitute
                          (with notice or lapse of time or both) a default (or
                          give rise to any right of termination, cancellation or
                          acceleration) under its charter or organizational
                          documents or any material contract to which Newco is a
                          party, except where such violation, conflict or breach
                          would not, individually or in the aggregate, have a
                          material adverse effect on Newco; or

                  (iii)   result in the creation of, any Encumbrance upon any of
                          the properties or assets of Newco.

         3.1.5    APPROVALS: As of the date hereof, no permit, authorization,
                  consent or approval of or by, or any notification of or filing
                  with, any Person is required in connection with the execution,
                  delivery or performance of this Agreement by Newco. Newco has
                  full authority to conduct its business as contemplated in the
                  Business Plan and the Transaction Documents.

         3.1.6    DISCLOSURE: This Agreement does not contain any untrue
                  statement of a material fact or omit to state any material
                  fact necessary to make the statements contained herein not
                  misleading. Newco is not aware of any material contingency,
                  event or circumstance relating to its business or prospects,
                  which could have a material adverse effect thereon, in order
                  for the disclosure herein relating to Newco not to be
                  misleading in any material respect.

         3.1.7    NO BUSINESS; NO LIABILITIES: Newco has not conducted any
                  business or incurred any liabilities or obligations prior to
                  the date hereof, except solely in connection with its
                  organization and formation.

3.2      REPRESENTATIONS AND WARRANTIES OF THE STOCKHOLDERS: Each of the
         Stockholders hereby severally represents and warrants to Newco as
         follows as of the date hereof:

         3.2.1    ORGANIZATION: Such Stockholder is a corporation duly organized
                  and validly existing under the laws of its jurisdiction of
                  organization and has all the requisite corporate power and
                  authority to own and lease its respective properties, to carry
                  on its respective business as presently conducted and as
                  proposed to be conducted and to carry out the transactions
                  contemplated hereby.

         3.2.2    AUTHORITY:  Such Stockholder has full legal right, power
                  and authority to enter into this Agreement and to perform
                  its obligations hereunder, which have been duly authorized
                  by all requisite corporate action. This Agreement is the
                  valid and binding obligation of such Stockholder,

<PAGE>

                  enforceable against it in accordance with its terms except
                  as limited by applicable bankruptcy, insolvency,
                  reorganization,  moratorium and other laws of general
                  application affecting the enforcement of creditors' rights
                  generally, and except as enforcement of rights to indemnity
                  and contribution hereunder may be limited by United States
                  federal or state securities laws or principles of public
                  policy.

         3.2.3    NO CONFLICTS: The execution, delivery and performance by such
                  Stockholder of this Agreement, purchase of the Shares, and
                  compliance with the provisions hereof by such Stockholder will
                  not:

                  (i)     violate any provision of applicable law, statute,
                          rule or regulation known by and applicable to such
                          Stockholder or any ruling, writ, injunction, order,
                          judgment or decree of any court, arbitrator,
                          administrative agency or other governmental body
                          applicable to such Stockholder or any of its
                          properties or assets;

                  (ii)    conflict with or result in any breach of any of the
                          terms, conditions or provisions of, or constitute
                          (with notice or lapse of time or both) a default (or
                          give rise to any right of termination, cancellation or
                          acceleration) under the charter or organizational
                          documents of such Stockholder or any material contract
                          to which such Stockholder is a party, except where
                          such violation, conflict or breach would not,
                          individually or in the aggregate, have a material
                          adverse effect on such Stockholder; or

                  (iii)   result in the creation of, any Encumbrance upon any of
                          the properties or assets of such Stockholder.

         3.2.4    APPROVALS: As of the date hereof, no permit, authorization,
                  consent or approval of or by, or any notification of or filing
                  with, any Person is required in connection with the execution,
                  delivery or performance of this Agreement by such Stockholder.

         3.2.5    INVESTMENT REPRESENTATIONS: Such Stockholder is
                  sophisticated in transactions of this type and capable of
                  evaluating the merits and risks of its investment in Newco.
                  Such Stockholder has not been formed solely for the purpose
                  of making this investment and such Stockholder is acquiring
                  the Common Stock and Preferred Stock for investment for its
                  own account, not as a nominee or agent, and not with the
                  view to, or for resale in connection with, any distribution
                  of any part thereof. Such Stockholder understands that the
                  Shares have not been registered under the Securities

<PAGE>

                  Act or applicable state and foreign securities laws by
                  reason of a specific exemption from the registration
                  provisions of the Securities Act and applicable state and
                  foreign securities laws, the availability of which depends
                  upon, among other things, the bona fide nature of the
                  investment intent and the accuracy of such Stockholders'
                  representations as expressed herein. Such Stockholder
                  understands that no public market now exists for any of the
                  Shares and that there is no assurance that a public market
                  will ever exist for such Shares.


                                    CLAUSE 4

                            AUTHORIZATION AND CLOSING

4.1      Newco has authorized the issuance to (i) EIS of 2,980 shares of
         Preferred Stock and (ii) Photogen of 12,000 shares of Common Stock,
         issuable as provided in Clause 4.3 hereof.

4.2      Photogen and EIS hereby subscribe for the number of Shares set forth in
         Clause 4.1 and shall pay to Newco in consideration therefor, by wire
         transfer of immediately available funds (to a bank account established
         by Newco in connection with Completion) the subscription amounts each
         as provided in Clause 4.4.1.

4.3      The closing (the "CLOSING") shall take place at the offices of Brock
         Silverstein LLC at 800 Third Avenue, New York, New York 10022 on the
         date hereof or such other places if any, as the Parties may agree and
         shall occur contemporaneously with the closing under the Photogen
         Securities Purchase Agreement.

4.4      At the Closing, each of the Stockholders shall take or (to the extent
         within its powers) cause to be taken the following steps at directors
         and shareholder meetings of Newco, or such other meetings or locations,
         as appropriate:

         4.4.1    Newco shall issue and sell to EIS, and EIS shall purchase from
                  Newco, upon the terms and subject to the conditions set forth
                  herein, 2,980 shares of Preferred Stock for an aggregate
                  purchase price of $2,985,000. Newco shall issue and sell to
                  Photogen, and Photogen shall purchase from Newco, upon the
                  terms and conditions set forth herein, (i) 12,000 shares of
                  Common Stock for an aggregate purchase price of $12,015,000.

         4.4.2    the Parties shall execute and deliver to each other, as
                  applicable, certificates in respect of the Common Stock and
                  Preferred Stock described above and any other certificates,
                  resolutions or documents which the

<PAGE>

                  Parties shall reasonably require;

         4.4.3.   the adoption by Newco of Newco=s Memorandum of Association
                  and Bye-Laws;

         4.4.4.   the appointment of Kevin Insley, John Smolik and Eric
                  Wachter as Directors of Newco;

         4.4.5.   the resignation of all directors and the secretary of Newco
                  holding office prior to the execution of this Agreement and
                  delivery of written confirmation under seal by each Person
                  so resigning that he has no claim or right of action
                  against Newco and that Newco is not in any way obligated or
                  indebted to him; and

         4.4.6.   the transfer to Newco of the share register.

4.5      EXEMPTION FROM REGISTRATION:

         The Shares will be issued under an exemption or exemptions from
         registration under the Securities Act. Accordingly, the certificates
         evidencing the Shares shall, upon issuance, contain the following
         legend:

         THE SECURITIES REPRESENTED HEREBY HAVE NOT BEEN
         REGISTERED UNDER THE SECURITIES ACT OF 1933, AS
         AMENDED, OR ANY SECURITIES LAWS OF A STATE OR OTHER
         JURISDICTION AND MAY NOT UNDER ANY CIRCUMSTANCES BE
         SOLD, TRANSFERRED, OR OTHERWISE DISPOSED OF (OTHER
         THAN TO AN AFFILIATE OF THE ORIGINAL HOLDER OR AS
         OTHERWISE PERMITTED IN THE AGREEMENT PURSUANT TO
         WHICH THEY WERE ISSUED) EXCEPT PURSUANT TO (i) AN
         EFFECTIVE REGISTRATION STATEMENT UNDER THE SECURITIES
         ACT AND ANY APPLICABLE STATE SECURITIES OR BLUE SKY
         LAWS, OR (ii) TO THE EXTENT APPLICABLE, RULE 144
         UNDER THE SECURITIES ACT (OR ANY SIMILAR RULE UNDER
         THE SECURITIES ACT RELATING TO THE DISPOSITION OF
         SECURITIES) TOGETHER WITH AN OPINION OF COUNSEL
         REASONABLY SATISFACTORY TO THE CORPORATION THAT
         REGISTRATION IS NOT REQUIRED UNDER SUCH ACT OR
         APPLICABLE STATE SECURITIES LAWS.

<PAGE>

4.6.     Newco shall use reasonable efforts to file any documents that require
         filing with the Registrar of Companies in Bermuda within the prescribed
         time limits. EIS and Photogen shall provide all reasonable co-operation
         to Newco in relation to the matters set forth in this Clause 4.6.

4.7.     In the event that EIS exercises the Exchange  Right prior to the
         third  anniversary  of the Closing Date as set forth in Section 5 of
         the Certificate of Designations,  and Photogen is required to
         transfer to EIS any shares of Common Stock,  Newco shall,
         immediately  upon such exercise,  take all necessary steps to ensure
         that each share to be  transferred  by Photogen  to EIS upon
         exercise  of the  Exchange  Right is duly and validly  issued and
         that EIS has full legal  right,  title and  interest in and to such
         shares of Preferred Stock  thereby  exchanged.  The Parties
         acknowledge  that such Shares have been pledged to EIS pursuant to
         the Photogen  Securities  Purchase Agreement and that EIS has
         physical possession of such Shares; upon such exercise,  EIS shall
         be entitled to keep and retain  such  shares,  which shall be owned
         by EIS as provided above.  In  connection  with  the  foregoing,
         Newco  and the  Participants  shall  take all  necessary  or
         appropriate steps to ensure such ownership by EIS.

                                    CLAUSE 5

                    DIRECTORS; MANAGEMENT AND R&D COMMITTEES

5.1.     DIRECTORS:

         5.1.1    Prior to the exercise of the Exchange Right, the Board shall
                  be composed of three Directors.

                  Photogen shall have the right to nominate two directors of
                  Newco, ("PHOTOGEN DIRECTORS") and EIS shall have the right to
                  nominate one Director of Newco ("EIS DIRECTOR") which
                  Director, [****]. To the extent required by applicable Bermuda
                  law, in the event that the EIS Director is not a resident of
                  Bermuda, at least one Photogen Director shall be a resident of
                  Bermuda

                  [****]

                  [****]

         5.1.2    If EIS removes the EIS Director, or Photogen removes any of
                  the Photogen Directors, EIS or Photogen, as the case may be,
                  shall indemnify the other Stockholder against any claim by
                  such removed Director arising

<PAGE>

                  from such removal.

         5.1.3    The Directors shall meet not less than three times in each
                  Financial Year and all Board meetings shall be held in Bermuda
                  to the extent required pursuant to the laws of Bermuda or to
                  ensure the sole residence of Newco in Bermuda provided that
                  Directors may attend such meetings telephonically.

----------------

[****]   REPRESENTS MATERIAL WHICH HAS BEEN REDACTED PURSUANT TO A REQUEST
         FOR CONFIDENTIAL TREATMENT PURSUANT TO RULE 24B-2 UNDER THE
         SECURITIES EXCHANGE ACT OF 1934, AS AMENDED.

<PAGE>

         5.1.4    At any such meeting, the presence of the EIS Director and at
                  least one of the Photogen Directors shall be required to
                  constitute a quorum and, subject to Clause 18 hereof, the
                  affirmative vote of a majority of the Directors present at a
                  meeting at which such a quorum is present shall constitute an
                  action of the Directors. In the event of any meeting being
                  inquorate, the meeting shall be adjourned for a period of
                  seven days. A notice shall be sent to the EIS Director and the
                  Photogen Directors specifying the date, time and place where
                  such adjourned meeting is to be held and reconvened.

         5.1.5    [****]

                  (i)      [****]

                  (ii)     [****]

                  (in each case the "CHAIRMAN STATUS BOARD MEETING")

                  [****]

                  If the chairman is unable to attend any meeting of the Board
                  held prior to the Chairman Status Board Meeting, the Photogen
                  Directors shall be entitled to appoint another Photogen
                  Director to act as chairman in his place at the meeting.

                  If the chairman of Newco is unable to attend any meeting of
                  the Board held after the Chairman Status Board Meeting, the
                  Directors shall be entitled to appoint another Director to act
                  as chairman of Newco in his place at the meeting.

         5.1.6    In case of an equality of votes at a meeting of the Board, the
                  chairman of Newco shall not be entitled to a second or casting
                  vote. In the event of continued deadlock, the Board shall
                  resolve the deadlock pursuant to the provisions set forth in
                  Clause 19.

----------------

[****]   REPRESENTS MATERIAL WHICH HAS BEEN REDACTED PURSUANT TO A REQUEST
         FOR CONFIDENTIAL TREATMENT PURSUANT TO RULE 24B-2 UNDER THE
         SECURITIES EXCHANGE ACT OF 1934, AS AMENDED.

<PAGE>

5.2      MANAGEMENT AND R&D COMMITTEES:

         5.2.1    The Board shall appoint a management committee (the
                  "MANAGEMENT COMMITTEE") to consist of four members, two of
                  whom shall be nominated by Elan and two of whom shall be
                  nominated by Photogen, and each of whom shall be entitled to
                  one vote, whether or not present at any Management Committee
                  meeting. Decisions of the Management Committee shall require
                  the approval of all four members of the Management Committee.

                  Elan and Photogen shall be entitled to remove any of their
                  nominees to the Management Committee and appoint a replacement
                  in place of any nominees so removed. The number of members of
                  the Management Committee may be altered if agreed to by a
                  majority of the Directors and of the shareholders of Newco;
                  provided that, each of Elan and Photogen shall be entitled to
                  appoint an equal number of members to the Management
                  Committee. The Management Committee shall be responsible for,
                  INTER ALIA, devising, implementing and reviewing strategy for
                  the Project.

         5.2.2    The Management Committee shall appoint a research and
                  development committee (the "R&D COMMITTEE"), which shall be
                  comprised of four members, two of whom shall be nominated by
                  Elan and two of whom shall be nominated by Photogen, and each
                  of whom shall have one vote, whether or not present at an R&D
                  Committee meeting during which research and development issues
                  are discussed. Decisions of the R&D Committee shall require
                  approval of all four members of the R&D Committee.

                  Elan and Photogen shall be entitled to remove any of their
                  nominees to the R&D Committee and appoint a replacement in
                  place of any nominees so removed. The number of members of the
                  R&D Committee may be altered if agreed to by a majority of the
                  directors and shareholders of Newco provided that each of Elan
                  and Photogen shall be entitled to appoint an equal number of
                  members to the R&D Committee.

         5.2.3    The R&D Committee shall be responsible for:-

                  (i)      designing that portion of the Business Plan that
                           relates to the Project for consideration by the
                           Management Committee;

                  (ii)     establishing a joint Project team consisting of an
                           equal number of team members from Elan and Photogen,
                           including one Project leader from each of Elan and
                           Photogen; and

<PAGE>

                  (iii)    implementing such portion of the Business Plan that
                           relates to the Project, as approved by the Management
                           Committee.

         5.2.4    In the event of any dispute amongst the R&D Committee, the R&D
                  Committee shall refer such dispute to the Management Committee
                  whose decision on the dispute shall be binding on the R&D
                  Committee.

                  If the Management Committee cannot resolve the matter, the
                  dispute will be referred to a designated senior officer of
                  each of Elan and Photogen, and thereafter, in the event of
                  continued deadlock, pursuant to the deadlock provisions to be
                  set forth in Clause 19, involving inter alia, the referral of
                  the dispute to an expert, whose decision, however, will
                  ultimately be non-binding on the Participants. This process
                  shall also apply to any dispute within the Management
                  Committee.

                  Any ultimate deadlock within the Management Committee or the
                  Board (subject to applicable laws and the bye-laws of Newco)
                  will be settled by binding arbitration pursuant to Clause 24.

         5.2.5    Elan and Photogen shall permit Newco or its duly authorized
                  representative on reasonable notice and at any reasonable
                  time during normal business hours to have access to inspect
                  and audit the accounts and records of Elan or Photogen and any
                  other book, record, voucher, receipt or invoice relating to
                  the calculation or the cost of the R&D Program and to the
                  accuracy of the reports which accompanied them. Any such
                  inspection of Elan's or Photogen's records, as the case may
                  be, shall be at the expense of Newco, except that if such
                  inspection reveals an overpayment in the amount paid to Elan
                  or Photogen, as the case may be, for the R&D Program hereunder
                  in any Financial Year of [****]% or more of the amount due to
                  Elan or Photogen, as the case may be, then the expense of such
                  inspection shall be borne [****] by Elan or Photogen, as the
                  case may be, instead of by Newco.  Any surplus over the sum
                  properly payable by Newco to Elan or Photogen, as the case may
                  be, shall be paid promptly by Elan or Photogen, as the case
                  may be, to Newco.  If such inspection reveals a deficit in the
                  amount of the sum properly payable to Elan or Photogen, as
                  the case may be, by Newco, Newco shall pay the deficit to Elan
                  or Photogen, as the case may be.

----------------

[****]   REPRESENTS MATERIAL WHICH HAS BEEN REDACTED PURSUANT TO A REQUEST
         FOR CONFIDENTIAL TREATMENT PURSUANT TO RULE 24B-2 UNDER

<PAGE>

         THE SECURITIES EXCHANGE ACT OF 1934, AS AMENDED.

<PAGE>

                                    CLAUSE 6

                          THE BUSINESS PLAN AND REVIEWS

6.1      The Directors shall meet together as soon as reasonably practicable
         after the Closing Date hereof and shall agree upon and approve the
         Business Plan for the current Financial Year within 60 days of the
         Closing Date.

6.2      The Business Plan shall be reviewed and agreed by the unanimous
         approval of the EIS Director and of Photogen Directors on a quarterly
         basis.

6.3.     Neither Participant shall be obliged to provide funding to Newco in the
         absence of quarterly approval of the Business Plan and a determination
         by each Participant, in its sole discretion, that Subsequent Funding
         (as such term is defined in the Funding Agreement) shall be provided
         for the development of the Products.

                                    CLAUSE 7

                          RESEARCH AND DEVELOPMENT WORK

7.1      Subject to the provisions of Clause 6.3, Elan and Photogen, at Newco's
         request, may undertake research and development work related to the
         development and commercialization of the Products, at the request of
         Newco and as articulated in the Business Plan, in furtherance of the
         development and commercialisation of the Products and cultivation of
         patent rights and know-how related to the Elan Intellectual Property,
         Photogen Intellectual Property and Newco Intellectual Property.

7.2      The cost of such development work shall be Elan's and Photogen's, as
         the case may be, [****] costs in respect thereof, [****] of such costs.
         Research and development work that is sub-contracted by Elan or
         Photogen to third party providers shall be charged by Elan or Photogen
         to Newco at the amount invoiced by the relevant third party provider.

7.3      [****]

----------------

<PAGE>

[****]   REPRESENTS MATERIAL WHICH HAS BEEN REDACTED PURSUANT TO A REQUEST
         FOR CONFIDENTIAL TREATMENT PURSUANT TO RULE 24B-2 UNDER THE
         SECURITIES EXCHANGE ACT OF 1934, AS AMENDED.

<PAGE>

                                    CLAUSE 8

                                COMMERCIALIZATION

8.1      Newco shall diligently pursue the research, development, prosecution
         and commercialization of the Products, as provided in the Business
         Plan.

8.2      [****]

         [****]

         If Newco has not entered into an agreement with a third party within
         the 6 month period described above, the Elan/Newco Option shall be
         deemed to have re-commenced upon the same terms as set forth herein.

                                    CLAUSE 9

                        SUBLICENSE AND ASSIGNMENT RIGHTS

9.1      Newco shall not be permitted to assign, license or sublicense any of
         its rights in respect of the Newco Intellectual Property without the
         prior written consent of Elan and Photogen, as the case may be, which
         consent will not be unreasonably withheld or delayed; PROVIDED THAT
         Elan shall in all cases, in its sole discretion, be entitled to
         withhold its consent in the case of a proposed sublicense to any
         Technological Competitor to Elan.

9.3      The Parties acknowledge and agree to be bound by the provisions of
         Clause 2.5 of the Elan License Agreement and the provisions of Clause
         2.7 of the Photogen License Agreement which set forth the agreement
         between the Parties thereto in relation to sub-licensing of the Elan
         Intellectual Property and the Photogen Intellectual Property
         respectively.

----------------

[****]   REPRESENTS MATERIAL WHICH HAS BEEN REDACTED PURSUANT TO A REQUEST
         FOR CONFIDENTIAL TREATMENT PURSUANT TO RULE 24B-2 UNDER THE
         SECURITIES EXCHANGE ACT OF 1934, AS AMENDED.

<PAGE>

                                    CLAUSE 10

                OWNERSHIP OF INTELLECTUAL PROPERTY RIGHTS /[****]

10.1     The Parties acknowledge and agree to be bound by the provisions of
         Clause 3.1 of the Elan License Agreement and Clause 3.1 of the Photogen
         License Agreement which set forth the agreement between the parties
         thereto in relation to the ownership of the Elan Intellectual Property,
         the Photogen Intellectual Property and the Newco Intellectual property
         respectively.

10.2     The Parties acknowledge and agree to be bound by the provisions the
         provisions of Clause 4 of the Elan License Agreement and the provisions
         of Clause 4 of the Photogen License Agreement which set forth the
         agreement between the parties thereto in relation to the [****]
         obligations of Elan and Photogen, respectively.

                                    CLAUSE 11

                          INTELLECTUAL PROPERTY RIGHTS

11.1     Subject to Clause 11.8 herein, Elan has the sole and exclusive right,
         at its sole discretion and at its cost and expense, to prepare, file,
         prosecute, enforce, maintain, and protect against infringement or
         unauthorized use of all such Elan Patent Rights, and any other Elan
         Intellectual Property.

11.2     Subject to Clause 11.8 herein, Photogen, at its cost and expense, shall
         prepare, file, prosecute, enforce, maintain, and protect against
         infringement or unauthorized use of all such Photogen Patent Rights,
         and any other Photogen Intellectual Property.

11.3     Title and all other ownership rights to the GynNyc Intellectual
         Property, including the Patent Rights, shall be governed by the General
         Nycomed Agreement

11.4     Newco, at its cost and expense, shall prepare, file, prosecute and
         maintain and protect against infringement of all patents and patent
         applications relating to Newco Intellectual Property. Newco shall
         timely appraise both Photogen and Elan in writing of any such activity
         prior to occurrence of the same.

----------------

[****]   REPRESENTS MATERIAL WHICH HAS BEEN REDACTED PURSUANT TO A REQUEST
         FOR CONFIDENTIAL TREATMENT PURSUANT TO RULE 24B-2 UNDER THE
         SECURITIES EXCHANGE ACT OF 1934, AS AMENDED.

<PAGE>

11.5     In the event that a Party informs the other Parties that it does not
         intend to file patent applications on patentable inventions and
         discoveries within the Photogen or Elan Intellectual Property as the
         case may be, in the Field in one or more countries in the Territory or
         fails to file such an application within a reasonable period of time,
         Newco shall have the option at its expense to file and prosecute such
         patent application(s) in the joint names of Newco and the Party not
         intending or failing to so file. Upon written request from Newco, such
         Party shall execute all documents, forms and declarations and to do all
         things as shall be reasonably necessary to enable Newco to exercise
         such option.

11.6     In the event that Newco informs both Elan and Photogen that it does not
         intend to file an application on the Newco Intellectual Property in or
         outside the Field, Elan shall have the right to file and prosecute such
         inventions that Elan invents solely and Photogen shall have the right
         to file and prosecute such patent applications on inventions which
         Photogen invents solely and Elan and Photogen agree to negotiate in
         good faith on the course of action to be taken with respect to Newco
         Intellectual Property that both Elan and Photogen invent.

11.7     The Parties shall promptly inform each other in writing of any alleged
         infringement of any patents within the Elan Patents, the Photogen
         Patents or the Newco Patents or the GenNyc Intellectual Property or any
         alleged misappropriation of trade secrets within the Elan Intellectual
         Property, the Photogen Intellectual Property by a third party of which
         it becomes aware and provide the others with any available evidence of
         such infringement or misappropriation.

11.8     Newco shall have the right to enforce at its own expense and for its
         own benefit the Elan Patents and the Photogen Patents or
         misappropriation of the Elan Intellectual Property and the Photogen
         Intellectual Property, against any third party infringement or
         misappropriation, insofar as such infringements or misappropriation
         relates solely to the Field. In the event that Newco takes such action,
         Newco shall do so at its own cost and expense. At Newco's request, the
         Parties shall cooperate with such action. Any recovery remaining after
         the deduction by Newco of the reasonable expenses (including attorney's
         fees and expenses) incurred in relation to such infringement proceeding
         shall belong to Newco. Should Newco decide not to pursue such
         infringers, within a reasonable period but in any event within sixty
         (60) days after receiving written notice of such alleged infringement
         or misappropriation either Party may in its discretion initiate such
         proceedings in its own name, at its expense and for its own benefit,
         and at such Party's request, Newco shall cooperate with such action.

<PAGE>

         Alternatively, the Parties may agree to institute such proceedings in
         their joint names and shall reach agreement as to the proportion in
         which they shall share the proceeds of any such proceedings, and the
         expense of any costs not recovered, or the costs or damages payable to
         the third party. If the infringement of the Elan Patents or the
         Photogen Patents affects both the Field as well as other products being
         developed or commercialized by Photogen or Elan or its commercial
         partners outside the Field, Photogen or Elan shall endeavor to agree as
         to the manner in which the proceedings should be instituted and as to
         the proportion in which they shall share the proceeds of any such
         proceedings, and the expense of any costs not recovered, or the costs
         or damages payable to the third party.

11.9     Newco shall have the first right but not the obligation to bring suit
         or otherwise take action against any alleged infringement of the Newco
         Patents or alleged misappropriation of the Newco Intellectual Property.
         If any such alleged infringement or misappropriation occurs that gives
         rise to a cause of action both inside and outside the Field, Newco, in
         consultation with the other Parties, shall determine the cause of
         action to be taken. In the event that Newco takes such action, Newco
         shall do so at its own cost and expense and all damages and monetary
         award recovered in or with respect to such action shall be the property
         of Newco. Newco shall keep Elan and Photogen informed of any action in
         a timely manner so as to enable Photogen and Elan to provide input in
         any such action and Newco shall reasonably take into consideration any
         such input. At Newco's request, the Parties shall cooperate with any
         such action at Newco=s cost and expense.

11.10    In the event that Newco does not bring suit or otherwise take action
         against all infringement of the Newco Patents or misappropriation of
         the Newco Intellectual Property (i) if only one Party determines to
         pursue such suit or take such action at its own cost and expense, it
         shall be entitled to all damages and monetary award recovered in or
         with respect to such action and (ii) if the other Parties pursue such
         suit or action outside of Newco, they shall negotiate in good faith an
         appropriate allocation of costs, expenses and recovery amounts.

         In the event that a claim is or proceedings are brought against Newco
         by a third party alleging that the sale, distribution or use of a
         Product in the Territory or use of the Elan Intellectual Property or
         the Photogen Intellectual Property, as the case may be, infringes the
         intellectual property rights of such Party, Newco shall promptly advise
         the other Parties of such threat or suit.

11.11    All actions of Newco required under this Clause 11 shall be
         determined by the unanimous action of the Management Committee.

<PAGE>

                                    CLAUSE 12

    CROSS-LICENSES / EXPLOITATION OF NEWCO INTELLECTUAL OUTSIDE THE FIELD

12.1     Solely for the purpose of and insofar as is necessary, in each case,
         for Elan to perform its obligations under the Elan License Agreement,
         Newco shall grant to Elan a [****] worldwide, [****], fully paid-up
         license for the term of the License Agreements:

         12.1.1   to use the Newco Intellectual Property in the Field, and

         12.1.2   subject to the terms and conditions of the Photogen License
                  Agreement, a [****] to use the Photogen Intellectual Property
                  in the Field, and subject to the terms and conditions of the
                  Photogen License Agreement and the General Nycomed Agreement,
                  the GenNyc Intellectual Property in the Field.

12.2     Solely for the purpose of and insofar as is necessary, in each case,
         for Photogen to perform its obligations to Newco under the Photogen
         License Agreement, Newco shall grant to Photogen a [****] worldwide,
         [****], fully paid-up license for the term of the License Agreements:

         12.2.1   to use the Newco Intellectual Property in the Field, and

         12.2.2   subject to the terms and conditions of the Elan License
                  Agreement, a sublicense to use the Elan Intellectual Property
                  in the Field.

12.3     Elan shall be entitled to exploit the Newco Intellectual Property
         outside the Field subject to the Parties negotiating a license
         agreement in good faith (including all material provisions thereof,
         including as to whether the license should be exclusive or
         non-exclusive), pursuant to which Newco will grant Elan a license under
         the Newco Intellectual Property outside the Field on a Product by
         Product basis. The financial terms of the said license agreement shall
         have regard, inter alia, to:

         12.3.1   the amount of monies expended by Newco in developing the
                  Newco Intellectual Property;

----------------

<PAGE>


[****]   REPRESENTS MATERIAL WHICH HAS BEEN REDACTED PURSUANT TO A REQUEST
         FOR CONFIDENTIAL TREATMENT PURSUANT TO RULE 24B-2 UNDER THE
         SECURITIES EXCHANGE ACT OF 1934, AS AMENDED.

         12.3.2   the materiality of the Newco Intellectual Property by
                  comparison to the further research and development work to be
                  conducted, and of the Elan Intellectual Property and the
                  Photogen Intellectual Property; and

         12.3.3   the financial return likely to be earned by Elan from the
                  proposed exploitation outside the Field; and

         12.3.4   the impact of the proposed exploitation of the Newco
                  Intellectual Property outside the Field on the exploitation of
                  the Newco Intellectual Property within the Field.

12.4     Photogen shall be entitled to exploit the Newco Intellectual Property
         outside the Field subject to the Parties negotiating a license
         agreement in good faith (including all material provisions thereof,
         including as to whether the license should be exclusive or
         non-exclusive), pursuant to which Newco will grant Photogen a license
         under the Newco Intellectual Property outside the Field on a Product by
         Product basis. The financial terms of the said license agreement shall
         have regard, inter alia, to:

         12.4.1   the amount of monies expended by Newco in developing the Newco
                  Intellectual Property;

         12.4.2   the materiality of the Newco Intellectual Property by
                  comparison to the further research and development work to be
                  conducted, and of the Elan Intellectual Property and the
                  Photogen Intellectual Property; and

         12.4.3   the financial return likely to be earned by Photogen from the
                  proposed exploitation outside the Field; and

         12.4.4   the impact of the proposed exploitation of the Newco
                  Intellectual Property outside the Field on the exploitation of
                  the Newco Intellectual Property within the Field.

                                    CLAUSE 13

                                   REGULATORY

13.1     Newco shall keep the other Parties promptly and fully advised of
         Newco's regulatory activities, progress and procedures. Newco shall
         inform the other Parties of any dealings it shall have with an RHA, and
         shall furnish the other Parties with copies of all correspondence
         relating to the Products. The Parties

<PAGE>

         shall collaborate to obtain any required regulatory approval of the RHA
         to market the Products.

13.2     Newco shall, at its own cost, file, prosecute and maintain any and all
         Regulatory Applications for the Products in the Territory in accordance
         with the Business Plan.

13.3     Subject to Clause 13.5, and subject to a determination by Newco that
         one or more Regulatory Approvals should be held in the name of Newco's
         commercial partner such as a sub-licensee, any and all Regulatory
         Approvals obtained hereunder for any Product shall remain the property
         of Newco, provided that Newco shall allow Elan and Photogen access
         thereto to enable Elan and Photogen to fulfill their respective
         obligations and exercise their respective rights under this Agreement.
         Newco shall maintain such Regulatory Approvals at its own cost.

13.4     It is hereby acknowledged that there are inherent uncertainties
         involved in the registration of pharmaceutical products with the RHA's
         insofar as obtaining approval is concerned and such uncertainties form
         part of the business risk involved in undertaking the form of
         commercial collaboration as set forth in this Agreement.

13.5     All Regulatory Approvals and the DMF (Drug Master File) relating to
         the Elan Intellectual Property shall be processed by and be the
         absolute property of Elan.

<PAGE>

                                    CLAUSE 14

                                  MANUFACTURING

Elan shall have the [****] right to manufacture and supply, and/or subcontract
the manufacture and supply of the Products.

A supply agreement with Elan shall be subject to negotiation and mutual
agreement by the Parties not later than the date of completion of Phase III (as
such term is commonly used in connection with FDA applications) of the R&D Plan.
The terms of the said supply agreements shall be on [****] terms, and shall be
negotiated in good faith by the Parties thereto.

[****]

[****]

                                    CLAUSE 15

                        TECHNICAL SERVICES AND ASSISTANCE

15.1     Whenever commercially and technically feasible, Newco shall contract
         with Photogen or Elan, as the case may be, to perform such other
         services as Newco may require, other than those specifically dealt with
         hereunder or in the License Agreements. In determining which Party
         should provide such services, the Management Committee shall take into
         account the respective infrastructure, capabilities and experience of
         Elan and Photogen. There shall be no obligation upon either of Photogen
         or Elan to perform such services.

----------------

[****]   REPRESENTS MATERIAL WHICH HAS BEEN REDACTED PURSUANT TO A REQUEST
         FOR CONFIDENTIAL TREATMENT PURSUANT TO RULE 24B-2 UNDER THE
         SECURITIES EXCHANGE ACT OF 1934, AS AMENDED.

<PAGE>

15.2     Newco shall, if the Participants so agree, conclude an administrative
         support agreement with Elan and/or Photogen on such terms as the
         Parties thereto shall in good faith negotiate. The administrative
         services shall include one or more of the following administrative
         services as requested by Newco:

         15.2.1   accounting, financial and other services;

         15.2.2   tax services;

         15.2.3   insurance services;

         15.2.4   human resources services;

         15.2.5   legal and company secretarial services;

         15.2.6   patent and related intellectual property services; and

         15.2.7   all such other services consistent with and of the same type
                  as those services to be provided pursuant to this Agreement,
                  as may be required.

         The foregoing list of services shall not be deemed exhaustive and may
         be changed from time to time upon written request by Newco.

15.3.    The Parties agree that each Party shall effect and maintain
         comprehensive general liability insurance in respect of all clinical
         trials and other activities performed by them on behalf of Newco. The
         Stockholders and Newco shall ensure that the industry standard
         insurance policies shall be in place for all activities to be carried
         out by Newco.

15.4     If Elan or Photogen so requires, Photogen or Elan, as the case may be,
         shall receive, at times and for periods mutually acceptable to the
         Parties, employees of the other Party (such employees to be acceptable
         to the receiving Party in the matter of qualification and competence)
         for instruction in respect of the Elan Intellectual Property or the
         Photogen Intellectual Property, as the case may be, as necessary to
         further the Project.

15.5     The employees received by Elan or Photogen, as the case may be, shall
         be subject to obligations of confidentiality no less stringent than
         those set out in Clause 22 and such employees shall observe the rules,
         regulations and systems adopted by the Party receiving the said
         employees for its own employees or visitors.

<PAGE>

                                    CLAUSE 16

                      AUDITORS, BANKERS, REGISTERED OFFICE,
                  ACCOUNTING REFERENCE DATE; SECRETARY; COUNSEL

Unless otherwise agreed by the Stockholders and save as may be provided to the
contrary herein:

16.1     the auditors of Newco shall be [****];

16.2     the bankers of Newco shall be [****] or such other bank as may be
         mutually agreed from time to time;

16.3     the accounting reference date of Newco shall be December 31st in
         each Financial Year; and

16.4     the secretary of Newco shall be [****] or such other Person as may
         be appointed by the Directors  from time to time.

                                    CLAUSE 17

                              TRANSFERS OF SHARES;
                     RIGHT OF FIRST OFFER; TAG ALONG RIGHTS

GENERAL:

17.1.    No Stockholder shall, directly or indirectly, sell or otherwise
         transfer (each, a "TRANSFER") any Shares held by it except in as
         expressly permitted by and accordance with the terms of this Agreement.
         Newco shall not, and shall not permit any transfer agent or registrar
         for any Shares to, transfer upon the books of Newco any Shares from any
         Stockholder to any transferee, in any manner, except in accordance with
         this Agreement, and any purported transfer not in compliance with this
         Agreement shall be void.

----------------

[****]   REPRESENTS MATERIAL WHICH HAS BEEN REDACTED PURSUANT TO A REQUEST
         FOR CONFIDENTIAL TREATMENT PURSUANT TO RULE 24B-2 UNDER THE
         SECURITIES EXCHANGE ACT OF 1934, AS AMENDED.

<PAGE>

         During the R&D Term, no Stockholder shall, directly or indirectly, sell
         or otherwise Transfer any of its legal and/or beneficial interest in
         the Shares held by it to any other Person. After completion of the R&D
         Term, a Stockholder may Transfer Shares provided such Stockholder
         complies with the provisions of Clauses 17.2 and 17.3.

         Notwithstanding anything contained herein to the contrary, at all
         times, EIS and/or Photogen shall have the right to Transfer any Shares
         to their Affiliates provided, however, that such assignment does not
         result in adverse tax consequences for any other Parties. EIS shall
         have the right to Transfer any Shares to an Affiliate or special
         purpose financing or similar entity established by Elan or EIS;
         provided, that such Affiliates or special purpose financing or similar
         entity shall agree to be expressly subject to and bound by all the
         limitations and provisions which are embodied in this Agreement.

17.2     No Stockholder shall, except with the prior written consent of the
         other Stockholder, create or permit to subsist any Encumbrance over or
         in, all or any of the Shares held by it (other than by a Transfer of
         such Shares in accordance with the provisions of this Agreement).

17.3     No Stockholder shall, except with the prior written consent of the
         other Stockholder, create or permit to subsist any pledge, lien or
         charge over, or grant any option or other rights in all or any of the
         Shares held by it (other than by a Transfer of such Shares in
         accordance with the provisions of this Agreement) made by it to Newco
         unless any Person in whose favour any such pledge, lien, or charge is
         created or permitted to subsist or such option or rights are granted or
         such interest is disposed of shall be expressly subject to and bound by
         all the limitations and provisions which are embodied in this
         Agreement.

17.4     RIGHTS OF FIRST OFFER:

         If at any time after the end of the R&D Term a Stockholder shall desire
         to Transfer any Shares owned by it (a "SELLING STOCKHOLDER"), in any
         transaction or series of related transactions other than a Transfer to
         an Affiliate or subsidiary or in the case of EIS to a special purpose
         financing or similar entity established by EIS, then such Selling
         Stockholder shall deliver prior written notice of its desire to
         Transfer (a "NOTICE OF INTENTION") (i) to Newco and (ii) to the
         Stockholders who are not the Selling Stockholder (and any transferee
         thereof permitted hereunder, if any), as applicable, setting forth such
         Selling Stockholder's desire to make such Transfer, the number of
         Shares proposed to be transferred (the "OFFERED SHARES") and the
         proposed form of transaction (the "TRANSACTION PROPOSAL"), together
         with any available documentation relating thereto, if any, and the
         price at which such Selling Stockholder proposes to Transfer the
         Offered

<PAGE>

         Shares (the "OFFER PRICE"). The "Right of First Offer" provided for
         in this Clause 17 shall be subject to any "Tag Along Right"
         benefiting a Stockholder which may be provided for by Clause 17,
         subject to the exceptions set forth therein.

         Upon receipt of the Notice of Intention, the Stockholders who are not
         the Selling Stockholder shall have the right to purchase at the Offer
         Price the Offered Shares, exercisable by the delivery of notice to the
         Selling Stockholder (the "NOTICE OF EXERCISE"), with a copy to Newco,
         within 10 business days from the date of receipt of the Notice of
         Intention. If no such Notice of Exercise has been delivered by the
         Stockholders who are not the Selling Stockholder within such
         10-business day period, or such Notice of Exercise does not relate to
         all of the Offered Shares covered by the Notice of Intention, then the
         Selling Stockholder shall be entitled to Transfer all of the Offered
         Shares to the intended transferee. In the event that all of the Offered
         Shares are not purchased by the non-selling Stockholders, the Selling
         Stockholder shall sell the available Offered Shares within 30 days
         after the delivery of such Notice of Intention on terms no more
         favorable to a third party than those presented to the non-selling
         Stockholders. If such sale does not occur, the Offered Shares shall
         again be subject to the Right of First Offer set forth in Clause 17.4.

         In the event that any of the Stockholders who are not the Selling
         Stockholder exercise their right to purchase all of the Offered Shares
         (in accordance with this Clause 17), then the Selling Stockholder shall
         sell all of the Offered Shares to such Stockholder(s), in the amounts
         set forth in the Notice of Intention, after not less than 10 business
         days and not more than 25 business days from the date of the delivery
         of the Notice of Exercise. In the event that more than one of the
         Stockholders who are not the Selling Stockholders wish to purchase the
         Offered Shares, the Offered Shares shall be allocated to such
         Stockholders on the basis of their pro rata equity interests in Newco.

         The rights and obligations of each of the Stockholders pursuant to the
         Right of First Offer provided herein shall terminate upon the date that
         the Common Stock is registered under Section 12(b) or 12(g) of the
         Exchange Act.

         At the closing of the purchase of all of the Offered Shares by the
         Stockholders who are not the Selling Stockholder (scheduled in
         accordance with Clause 17), the Selling Stockholder shall deliver
         certificates evidencing the Offered Shares being sold, duly endorsed,
         or accompanied by written instruments of transfer in form reasonably
         satisfactory to the Stockholders who are not the Selling Stockholder,
         duly executed by the Selling Stockholder, free and clear of any adverse
         claims, against payment of the purchase price therefor in cash, and
         such other customary documents as shall be necessary in connection
         therewith.

<PAGE>

17.5     TAG ALONG RIGHTS:
         Subject to Clause 17.4, a Stockholder (the "TRANSFERRING STOCKHOLDER")
         shall not Transfer (either directly or indirectly), in any one
         transaction or series of related transactions, to any Person or group
         of Persons, any Shares, unless the terms and conditions of such
         Transfer shall include an offer to the other Stockholders (the
         "REMAINING STOCKHOLDERS"), to sell Shares at the same price and on the
         same terms and conditions as the Transferring Stockholder has agreed to
         sell its Shares (the "TAG ALONG RIGHT").

         In the event a Transferring Stockholder proposes to Transfer any Shares
         in a transaction subject to this Clause 17.5, it shall notify, or cause
         to be notified, the Remaining Stockholders in writing of each such
         proposed Transfer. Such notice shall set forth: (i) the name of the
         transferee and the amount of Shares proposed to be transferred, (ii)
         the proposed amount and form of consideration and terms and conditions
         of payment offered by the transferee (the "TRANSFEREE TERMS") and (iii)
         that the transferee has been informed of the Tag Along Right provided
         for in this Clause 17, if such right is applicable, and the total
         number of Shares the transferee has agreed to purchase from the
         Stockholders in accordance with the terms hereof.

         The Tag Along Right may be exercised by each of the Remaining
         Stockholders by delivery of a written notice to the Transferring
         Stockholder (the "CO-SALE NOTICE") within 10 business days following
         receipt of the notice specified in the preceding subsection. The
         Co-sale Notice shall state the number of Shares owned by such Remaining
         Stockholder which the Remaining Stockholder wishes to include in such
         Transfer; provided, however, that without the written consent of the
         Transferring Stockholder, the amount of such securities belonging to
         the Remaining Stockholder included in such Transfer may not be greater
         than such Remaining Stockholder's percentage beneficial ownership of
         Fully Diluted Common Stock multiplied by the total number of shares of
         Common Stock to be sold by both the Transferring Stockholder and all
         Remaining Stockholders. Upon receipt of a Co-sale Notice, the
         Transferring Stockholder shall be obligated to transfer at least the
         entire number of Shares set forth in the Co-sale Notice to the
         transferee on the Transferee Terms; provided, however, that the
         Transferring Stockholder shall not consummate the purchase and sale of
         any Shares hereunder if the transferee does not purchase all such
         Shares specified in all Co-sale Notices. If no Co-sale Notice has been
         delivered to the Transferring Stockholder prior to the expiration of
         the 10 business day period referred to above and if the provisions of
         this Section have been complied with in all respects, the Transferring
         Stockholder shall have the right for a 30 day calendar day period to
         Transfer Shares to the transferee on the Transferee Terms without
         further notice to any other party, but after such 30-day period, no
         such Transfer may be made without again giving notice to the Remaining
         Stockholders of the proposed Transfer and

<PAGE>

         complying with the requirements of this Clause 17.

         At the closing of any Transfer of Shares subject to this Clause 17, the
         Transferring Stockholder, and the Remaining Stockholder, in the event
         such Tag Along Right is exercised, shall deliver certificates
         evidencing such securities as have been Transferred by each, duly
         endorsed, or accompanied by written instruments of transfer in form
         reasonably satisfactory to the transferee, free and clear of any
         adverse claim, against payment of the purchase price therefor.

         Notwithstanding the foregoing, this Clause 17 shall not apply to any
         sale of Common Stock pursuant to an effective registration statement
         under the Securities Act in a bona fide public offering.

                                   CLAUSE 18

                    MATTERS REQUIRING PARTICIPANTS' APPROVAL

18.1     In consideration of Photogen and Elan agreeing to enter into the
         License Agreements, the Parties hereby agree that Newco shall not
         without the prior approval of the EIS Director and all of the Photogen
         Directors:

         18.1.1.  make a material Newco determination outside the ordinary
                  course of business, including, among other things,
                  acquisitions or dispositions of intellectual property and
                  licenses or sublicenses, changes in the Business or the Newco
                  budget; entry into joint ventures and similar arrangements as
                  they relate to the Licensed Technologies and changes to the
                  Business Plan as they relate to the Licensed Technologies;

         18.1.2.  issue any unissued Shares or unissued Common Stock
                  Equivalents, or create or issue any new shares (including a
                  split of the Shares) or Common Stock Equivalents, except as
                  expressly permitted by the Newco Memorandum of Association
                  and Bye-Laws (it being agreed that Newco shall not issue
                  additional shares of authorized but unissued shares of
                  Preferred Stock without the prior approval of the EIS
                  Director and all of the Photogen Directors except to the
                  extent provided for in the Transaction Documents);

         18.1.3.  alter any rights attaching to any class of share in the
                  capital of Newco or alter the Newco Memorandum of Association
                  and Bye-Laws;

         18.1.4.  consolidate, sub-divide or convert any of Newco's share
                  capital or in

<PAGE>
                    any way alter the rights attaching thereto;

         18.1.5.    dispose of all or substantially all of the assets of Newco;

         18.1.6.    do or permit or suffer to be done any act or thing whereby
                    Newco may be wound up (whether voluntarily or compulsorily),
                    save as otherwise expressly provided for in this Agreement;

         18.1.7.    enter into any contract or transaction except in
                    the ordinary and proper course of the Business on
                    arm's length terms;

         18.1.8.    licence or sub-licence any of the Elan Intellectual
                    Property, Photogen Intellectual Property, Newco
                    Intellectual Property;

         18.1.9.    amend or vary the terms of the Photogen License Agreement
                    or the Elan License Agreement;

         18.1.10.   permit a person other than Newco to own a regulatory
                    approval relating to the Product(s);

         18.1.11.   approve, amend or vary the Business Plan or the Newco
                    budget;

         18.1.12.   alter the number of Directors; and

         18.1.13.   whether any shares of Newco shall be registered for public
                    trading with any governmental authority for public trading
                    in any securities market other than pursuant to demand
                    registration under the Registration Rights agreement
                    applicable to Newco.

                                    CLAUSE 19

                                    DISPUTES

19.1     Should any dispute or difference arise between Elan and Photogen, or
         between Elan or Photogen and Newco, during the period that this
         Agreement is in force, other than a dispute or difference relating to
         (i) the interpretation of any provision of this Agreement, (ii) the
         interpretation or application of law, or (iii) the ownership of any
         intellectual property, then any Party may forthwith give notice to the
         other Parties that it wishes such dispute or difference to be referred
         to the chief executive officer of Photogen and the President of EPT.

<PAGE>

19.2     In any event of a notice being served in accordance with Clause 19.1,
         each of the Participants shall within 14 days of the service of such
         notice prepare and circulate to the chief executive officer of each
         Participant a memorandum or other form of statement setting out its
         position on the matter in dispute and its reasons for adopting that
         position. Each memorandum or statement shall be considered by the chief
         executive officers of the Participants who shall endeavor to resolve
         the dispute. If the chief executive officers of the Participants agree
         upon a resolution or disposition of the matter, they shall each sign a
         statement which sets out the terms of their agreement. The Participants
         agree that they shall exercise the voting rights and other powers
         available to them in relation to Newco to procure that the agreed terms
         are fully and promptly carried into effect.

19.3     In the event the chief executive officers of the Participants are
         unable to resolve a dispute or difference when it is referred to them
         under Clause 19.1 which relates to the interpretation of this Agreement
         or any other Transaction Document or the compliance of the Parties with
         their legal obligations thereunder, such dispute or difference shall be
         referred to arbitration in accordance with Clause 24.8.3 hereof. If the
         dispute or difference does not relate to the interpretation of this
         Agreement or any other Transaction Document or the compliance of the
         Parties with their legal obligations thereunder, the provisions of
         Clause 24.8.2 shall govern.

                                    CLAUSE 20

                                   TERMINATION

20.1     This Agreement shall govern the operation and existence of
         Newco until:

         20.1.1   terminated by written agreement of all Parties hereto; or

         20.1.2   otherwise terminated in accordance with this Clause 20.

20.2     For the purpose of this Clause 20, a "RELEVANT EVENT" is committed
         or suffered by a Participant if:

         20.2.1   it commits a material breach of its obligations under this
                  Agreement or the applicable License and fails to remedy it
                  within 60 days of being specifically required in writing to do
                  so by the other Participant; provided, however, that if the
                  breaching Participant has proposed a course of action to
                  rectify the breach and is acting in good faith to rectify same
                  but has not cured the breach by the 60th day, such period
                  shall be extended by such period as is reasonably necessary to
                  permit the breach to be rectified; or

         20.2.2   a distress, execution, sequestration or other process is
                  levied or enforced

<PAGE>

                  upon or sued out against substantially all of its assets
                  which is not discharged or challenged within 30 days; or

         20.2.3   it is unable to pay its debts in the normal course of
                  business; or
         20.2.4   it ceases wholly or substantially to carry on its business,
                  otherwise than for the purpose of a reconstruction or
                  amalgamation, without the prior written consent of the other
                  Participant (such consent not to be unreasonably withheld); or

         20.2.5   the appointment of a liquidator, receiver, administrator,
                  examiner, trustee or similar officer of such Participant or
                  over all or substantially all of its assets under the law of
                  any applicable jurisdiction, including without limitation, the
                  United States of America, Bermuda or Ireland; or

         20.2.6   an application or petition for bankruptcy, corporate
                  re-organization, composition, administration, examination,
                  arrangement or any other procedure similar to any of the
                  foregoing under the law of any applicable jurisdiction,
                  including without limitation, the United States of America,
                  Bermuda or Ireland, is filed, and is not discharged within 60
                  days, or a Participant applies for or consents to the
                  appointment of a receiver, administrator, examiner or similar
                  officer of it or of all or a material part of its assets,
                  rights or revenues or the assets and/or the business of a
                  Participant are for any reason seized, confiscated or
                  condemned.

20.4     If either Participant commits or suffers a Relevant Event, the other
         Participant shall be entitled, within three months of the occurrence of
         the Relevant Event, to require the defaulting Participant (the
         "RECIPIENT PARTICIPANT") to sell on reasonable terms of payment to the
         non-defaulting Participant (the "PROPOSING PARTICIPANT") all (but not
         some only) of the Shares, held or beneficially owned by the Recipient
         Participant for an amount equal to [****]% of the fair market value of
         the Shares of the Recipient Participant (the "BUYOUT OPTION").

20.5     The Proposing Participant shall notify the Recipient Participant of the
         exercise of the Buyout Option, no later than 30 business days prior to
         the proposed exercise thereof, by delivering written notice to the
         Recipient Participant stating that the Buyout Option is exercised and
         the price at which the Proposing Participant is willing to purchase the
         Shares of the Recipient Participant.

----------------

[****]   REPRESENTS MATERIAL WHICH HAS BEEN REDACTED PURSUANT TO A REQUEST
         FOR CONFIDENTIAL TREATMENT PURSUANT TO RULE 24B-2 UNDER THE
         SECURITIES EXCHANGE ACT OF 1934, AS AMENDED.

<PAGE>

20.6     In the event that the Participants do not agree upon a purchase price
         for the Shares within five Business Days following the receipt by the
         Recipient Participant of written notice from the Proposing Participant
         pursuant to Clause 20.5 above, the Proposing Participant may contact
         the American Arbitration Association ("AAA"), sitting in New York City
         and request that an independent US-based arbitrator who is expert in
         valuation and the pharmaceutical/biotechnology industry be appointed
         within 10 Business Days. The AAA shall endeavor to select an arbitrator
         who is technically knowledgeable in the pharmaceutical/biotechnology
         industry (and who directly and through his affiliates, has no business
         relationship with, or shareholding in, either the Proposing Participant
         or the Recipient Participant). Promptly upon being notified of the
         arbitrator's appointment, the Proposing Participant and the Recipient
         Participant shall submit to the arbitrator details of their assessment
         of the fair market value for the Shares of the Recipient Participant
         together with such information as they think necessary to validate
         their assessment. The arbitrator shall notify the Recipient Participant
         of [****]% of the fair market value assessed by the Proposing
         Participant (the "PROPOSING PARTICIPANT PRICE") and shall notify the
         Proposing Participant of [****]% of the fair market value assessed by
         the Recipient Participant (the "RECIPIENT PARTICIPANT PRICE"). The
         Proposing Participant and the Recipient Participant shall then be
         entitled to make further submissions to the arbitrator within five
         Business Days explaining why the Recipient Participant Price or the
         Proposing Participant Price, as the case may be, is unjustified. The
         arbitrator shall thereafter meet with the Proposing Participant and the
         Recipient Participant and shall thereafter choose either the Recipient
         Participant Price or the Proposing Participant Price (but not any other
         price) as the purchase price for the Shares (the "PURCHASE PRICE") on
         the basis of which price the expert determines to be closer to [****]%
         of the fair market value for the Shares of the Recipient Participant.
         The arbitrator shall use his best efforts to determine the Purchase
         Price within 30 Business Days of his appointment. The Proposing
         Participant and the Recipient Participant shall bear the costs of the
         arbitrator equally provided that the arbitrator may, in his discretion,
         allocate all or a portion of such costs to one Party. Any decision of
         the arbitrator shall be final and binding.

20.7     The Proposing Participant shall purchase the Shares of the Recipient
         Participant by delivery of the Purchase Price in cash no later than the
         15th Business Day following determination of the Purchase Price by the
         expert.

----------------

[****]   REPRESENTS MATERIAL WHICH HAS BEEN REDACTED PURSUANT TO A REQUEST
         FOR CONFIDENTIAL TREATMENT PURSUANT TO RULE 24B-2 UNDER THE
         SECURITIES EXCHANGE ACT OF 1934, AS AMENDED.

<PAGE>

20.8     The Shares of the Recipient Participant so transferred shall be sold by
         the transferor as beneficial owner with effect from the date of such
         transfer free from any lien, charge or encumbrance with all rights and
         restrictions attaching thereto. If the Proposing Participant elects to
         purchase the Shares of the Recipient Participant, the Shares of the
         Recipient Participant shall be sold by the Recipient Participant as
         beneficial owner for a price equal to [****]% of the Purchase Price
         with effect from the date specified by the Proposing Participant in its
         notice of election free from any lien, charge or encumbrance together
         with all rights attaching thereto.

20.9     If the Proposing Participant exercises the Buyout Option, both parties
         will negotiate in good faith to agree to additional reasonable
         provisions and/or amendments to the License Agreements to protect the
         intellectual property rights of the Recipient Party.

20.10    If either Participant commits a Relevant Event, the other Stockholder
         shall have in addition to all other legal and equitable rights and
         remedies hereunder, the right to terminate this Agreement upon 30 days'
         written notice.

20.11    In the event of a termination of the Elan License Agreement and/or the
         Photogen License Agreement, both parties will negotiate in good faith
         to determine whether this Agreement should be terminated and if so,
         which provisions should survive termination.

20.12    The provisions of Clauses 1.1, 3, 6, 5.1, 10, 19, 20 and 22 shall
         survive the termination of this Agreement under this Clause 20.10 or by
         mutual consent pursuant to Clause 20.1 in accordance with their terms;
         all other terms and provisions of this Agreement shall cease to have
         effect and be null and void upon the termination of this Agreement
         under this Clause 20.10 or by mutual consent pursuant to Clause 20.1.

                                    CLAUSE 21

                                  SHARE RIGHTS

[****]

----------------

[****]   REPRESENTS MATERIAL WHICH HAS BEEN REDACTED PURSUANT TO A REQUEST
         FOR CONFIDENTIAL TREATMENT PURSUANT TO RULE 24B-2 UNDER THE
         SECURITIES EXCHANGE ACT OF 1934, AS AMENDED.

<PAGE>

                                    CLAUSE 22

                                 CONFIDENTIALITY

22.1     The Parties and/or Newco acknowledge and agree that it may be
         necessary, from time to time, to disclose to each other
         confidential and/or proprietary information, including without
         limitation, inventions, works of authorship, trade secrets,
         specifications, designs, data, know-how and other information,
         relating to the Field, the Products, present or future products,
         the Newco Intellectual Property, the Elan Intellectual Property or
         the Photogen Intellectual Property, as the case may be, methods,
         compounds, research projects, work in process, services, sales
         suppliers, customers, employees and/or business of the disclosing
         Party, whether in oral, written, graphic or electronic form
         (collectively "CONFIDENTIAL INFORMATION").

22.2     Any Confidential Information revealed by a Party to another Party shall
         be maintained as confidential and shall be used by the receiving Party
         exclusively for the purposes of fulfilling the receiving Party's rights
         and obligations under this Agreement, and for no other purpose.
         Confidential Information shall not include:

         22.2.1   information that is generally available to the public;

         22.2.2   information that is made public by the disclosing Party;

         22.2.3   information that is independently developed by the receiving
                  Party, as evidenced by such Party's records, without the aid,
                  application or use of the disclosing Party's Confidential
                  Information;

         22.2.4   information that is published or otherwise becomes part of the
                  public domain without any disclosure by the receiving Party,
                  or on the part of the receiving Party's directors, officers,
                  agents, representatives or employees;

         22.2.5   information that becomes available to the receiving Party on a
                  non-confidential basis, whether directly or indirectly, from a
                  source other than the disclosing Party, which source did not
                  acquire this information on a confidential basis;

         22.2.6   information which the receiving Party is required to disclose
                  pursuant to:

                  (i)      a valid order of a court or other governmental body
                           or any political

<PAGE>

                           subdivision thereof or as otherwise required by law,
                           rule or regulation;

                  (ii)     other requirement of law; provided,  however, that
                           if the receiving Party becomes legally required
                           to disclose any  Confidential  Information,  the
                           receiving  Party shall give the disclosing  Party
                           prompt  notice of such fact so that the
                           disclosing  Party may obtain a protective order
                           or confidential  treatment or other  appropriate
                           remedy  concerning any such  disclosure.  The
                           receiving Party shall fully  co-operate with the
                           disclosing  Party in  connection  with the
                           disclosing  Party's  efforts  to obtain any such
                           order or other remedy.  If any such  order or
                           other  remedy  does not  fully  preclude
                           disclosure,  the receiving  Party shall make such
                           disclosure  only to the extent that such
                           disclosure is legally required;

         22.2.7   information which was already in the possession of the
                  receiving Party at the time of receiving such information, as
                  evidenced by its records, provided such information was not
                  previously provided to the receiving party from a source which
                  was under an obligation to keep such information confidential;
                  or

         22.2.8   information that is the subject of a written permission to
                  disclose, without restriction or limitation, by the disclosing
                  Party.

22.3     Each Party agrees to disclose Confidential Information of another Party
         only to those employees, representatives and agents requiring knowledge
         thereof in connection with their duties directly related to the
         fulfilling of the Party's obligations under this Agreement, so long as
         such persons are under an obligation of confidentiality no less
         stringent than as set forth herein. Each Party further agrees to inform
         all such employees, representatives and agents of the terms and
         provisions of this Agreement and their duties hereunder and to obtain
         their consent hereto as a condition of receiving Confidential
         Information. Each Party agrees that it will exercise a reasonable
         degree of care and protection to preserve the proprietary and
         confidential nature of the Confidential Information disclosed by a
         Party. Each Party agrees that it will, upon request of another Party,
         return all documents and any copies thereof containing Confidential
         Information belonging to or disclosed by such other Party. Each Party
         shall promptly notify the other Parties upon discovery of any
         unauthorized use or disclosure of the other Parties' Confidential
         Information.

22.4     Notwithstanding the above, each Party may use or disclose Confidential
         Information disclosed to it by another Party to the extent such use or
         disclosure is reasonably necessary in filing or prosecuting patent
         applications, prosecuting or defending litigation, complying with
         patent applications, prosecuting or defending

<PAGE>

         litigation, complying with applicable governmental regulations or
         otherwise submitting information to tax or other governmental
         authorities, conducting clinical trials, or granting a permitted
         sub-license or otherwise exercising its rights hereunder; provided,
         that if a Party is required to make any such disclosure of the
         other Party's Confidential Information, other than pursuant to a
         confidentiality agreement, such Party shall inform the third party
         recipient of the terms and provisions of this Agreement and their
         duties hereunder and shall obtain their commitment to abide by the
         provisions of Clause 22 as a condition of releasing to the third
         party recipient the Confidential Information.

22.5     Any breach of this Clause 22 by any employee,  representative or
         agent of a Party is considered a breach by the Party itself.

22.6     The provisions relating to confidentiality in this Clause 22 shall
         remain in effect during the Term and for a period of [****] following
         the termination of this Agreement.

22.7     The Parties agree that the obligations of this Clause 22 are necessary
         and reasonable in order to protect the Parties= respective businesses,
         and each Party expressly agrees that monetary damages would be
         inadequate to compensate a Party for any breach by the other Party of
         its covenants and agreements set forth herein. Accordingly, the Parties
         agree and acknowledge that any such violation or threatened violation
         will cause irreparable injury to a Party and that, in addition to any
         other remedies that may be available, in law or in equity or otherwise,
         any Party shall be entitled to obtain injunctive relief against the
         threatened breach of the provisions of this Clause 22, or a
         continuation of any such breach by the other Party, specific
         performance and other equitable relief to redress such breach together
         with its damages and reasonable counsel fees and expenses to enforce
         its rights hereunder, without the necessity of proving actual or
         express damages.

                                    CLAUSE 23

                                      COSTS

22.1     Each Stockholder shall bear its own legal and other costs incurred in
         relation to preparing and concluding this Agreement and the Transaction
         Documents.

22.2     All other costs, legal fees, registration fees and other expenses
         relating to the transactions contemplated hereby, including the costs
         and expenses incurred in relation to the incorporation of Newco, shall
         be borne by Newco.

<PAGE>

----------------

[****]   REPRESENTS MATERIAL WHICH HAS BEEN REDACTED PURSUANT TO A REQUEST
         FOR CONFIDENTIAL TREATMENT PURSUANT TO RULE 24B-2 UNDER THE
         SECURITIES EXCHANGE ACT OF 1934, AS AMENDED.

<PAGE>

                                    CLAUSE 24

                                     GENERAL

24.1     GOOD FAITH:

         Each of the Parties hereto undertakes with the others to do all things
         reasonably within its power that are necessary or desirable to give
         effect to the spirit and intent of this Agreement.

24.2     FURTHER ASSURANCE:

         At the request of any of the Parties, the other Party or Parties shall
         (and shall use reasonable efforts to procure that any other necessary
         parties shall) execute and perform all such documents, acts and things
         as may reasonably be required subsequent to the signing of this
         Agreement for assuring to or vesting in the requesting Party the full
         benefit of the terms hereof.

24.3     NO REPRESENTATION:

         Each of the Parties hereto hereby acknowledges that in entering into
         this Agreement it has not relied on any representation or warranty
         except as expressly set forth herein or in any document referred to
         herein.

24.4     FORCE MAJEURE:

         Neither Party to this Agreement shall be liable for delay in the
         performance of any of its obligations hereunder if such delay is caused
         by or results from causes beyond its reasonable control, including
         without limitation, acts of God, fires, strikes, acts of war (whether
         war be declared or not), insurrections, riots, civil commotions,
         strikes, lockouts or other labor disturbances or intervention of any
         relevant government authority, but any such delay or failure shall be
         remedied by such Party as soon as practicable.

24.5     RELATIONSHIP OF THE PARTIES:

         Nothing contained in this Agreement is intended or is to be construed
         to constitute Elan/EIS and Photogen as partners, or Elan/EIS as an
         employee or agent of Photogen, or Photogen as an employee or agent of
         Elan/EIS.

<PAGE>

         No Party hereto shall have any express or implied right or authority to
         assume or create any obligations on behalf of or in the name of another
         Party or to bind another Party to any contract, agreement or
         undertaking with any third Party.

24.6     COUNTERPARTS:

         This Agreement may be executed in any number of counterparts, each of
         which when so executed shall be deemed to be an original and all of
         which when taken together shall constitute this Agreement.

24.7     NOTICES:

         Any notice to be given under this Agreement shall be sent in writing by
         registered or recorded delivery post or reputable overnight courier
         such as Federal Express or telecopied to:

         Elan/EIS at:

         Lincoln House, Lincoln Place, Dublin 2, Ireland
         Attention:        Vice President & General Counsel
         Elan Pharmaceutical Technologies,
         a division of Elan Corporation, plc
         Telephone:        353-1-709-4000
         Fax:              353-1-709-4124

         and

         Elan International Services, Ltd.
         102 St. James Court
         Flatts, Smiths FL04
         Bermuda
         Attention:        President
         Telephone:        441-292-9169
         Fax:              441-292-2224


         Photogen at:
         7327 Oak Ridge
         Knoxville
         TN3793
         USA

<PAGE>

         Attention:        Chief Executive Officer
         Telephone:        001 423 769 4011
         Fax:              001 423 769 4013

         with a copy to:

         Grippo & Elden
         Suite 3600
         227 West Monroe
         Chicago
         Illinois 60606
         USA
         Attention:        Theodore W Grippo
         Telephone         001 312 704 7720
         Fax:              001 312 558 1195


         Newco at:

         102 St. James Court
         Flatts, Smiths FL04
         Bermuda
         Attention:        Secretary
         Telephone:        441-292-9169
         Fax:              441-292-2224

         or to such other address(es) as may from time to time be notified by
         any Party to the others hereunder.

         Any notice sent by mail shall be deemed to have been delivered within
         three Business Days after dispatch or delivery to the relevant courier
         and any notice sent by telecopy shall be deemed to have been delivered
         upon confirmation of receipt. Notices of change of address shall be
         effective upon receipt. Notices by telecopy shall also be sent by
         another method permitted hereunder.

24.8     GOVERNING LAW; ARBITRATION

         24.8.1.  This Agreement shall be governed by and construed in
                  accordance with the laws of the State of New York.

         24.8.2.  The Parties will attempt in good faith to resolve any
                  dispute arising out of or relating to this Agreement
                  promptly by negotiation between executives of the Parties.
                  In the event that such negotiations do not result in a
                  mutually acceptable resolution, the Parties agree to
                  consider other dispute resolution mechanisms

<PAGE>

                  including mediation.

                  In the event that the Parties fail to agree on a mutually
                  acceptable dispute resolution mechanism within 90 days of
                  written notice of a dispute by one Party to the other
                  Party, any such dispute shall be finally settled by
                  arbitration pursuant to Clause 24.8.3.

         24.8.3   Any dispute under this Agreement (including any ultimate
                  deadlock within the Management Committee or the Board
                  (subject to applicable laws and the Newco Memorandum of
                  Association and Bye-Laws)) which is not settled by mutual
                  consent under Clause 24.8.2 shall be finally settled by
                  binding arbitration, conducted in accordance with the
                  Commercial Arbitration Rules of the American Arbitration
                  Association by one arbitrator appointed in accordance with
                  said rules. Such arbitrator shall be reasonably
                  satisfactory to each of the Parties; provided, that if the
                  Parties are unable to agree upon the identity of such
                  arbitrator within [****] days of demand by either Party,
                  then either Party shall have the right to petition a
                  presiding justice of the Supreme Court of New York, New
                  York County, to appoint an arbitrator.

                  The arbitration shall be held in New York, New York.

                  The arbitrator shall determine what discovery will be
                  permitted, consistent with the goal of limiting the cost
                  and time which the Parties must expend for discovery;
                  provided the arbitrator shall permit such discovery as he
                  deems necessary to permit an equitable resolution of the
                  dispute.

                  Any written evidence originally in a language other than
                  English shall be submitted in English translation
                  accompanied by the original or a true copy thereof.

                  The costs of the arbitration, including administrative and
                  arbitrator's fees, shall be shared equally by the Parties
                  and each Party shall bear its own costs and attorneys' and
                  witness' fees incurred in connection with the arbitration.

----------------

[****]   REPRESENTS MATERIAL WHICH HAS BEEN REDACTED PURSUANT TO A REQUEST
         FOR CONFIDENTIAL TREATMENT PURSUANT TO RULE 24B-2 UNDER THE
         SECURITIES EXCHANGE ACT OF 1934, AS AMENDED.

<PAGE>

                  In rendering judgement, the arbitrator shall be instructed
                  by the Parties that he shall be permitted to select solely
                  from between the proposals for resolution of the relevant
                  issue presented by each Party, and not any other proposal.

                  A disputed performance or suspended performances pending
                  the resolution of the arbitration must be completed within
                  30 days following the final decision of the arbitrators or
                  such other reasonable period as the arbitrator determine in
                  a written opinion.

                  Any arbitration under this Agreement shall be completed
                  within one year from the filing of notice of a request for
                  such arbitration.

                  The arbitration proceedings and the decision shall not be
                  made public without the joint consent of the Parties and
                  each Party shall maintain the confidentiality of such
                  proceedings and decision unless otherwise permitted by the
                  other Party.

                  The Parties agree that the decision shall be the sole,
                  exclusive and binding remedy between them regarding any and
                  all disputes, controversies, claims and counterclaims
                  presented to the arbitrator. Application may be made to any
                  court having jurisdiction over the Party (or its assets)
                  against whom the decision is rendered for a judicial
                  recognition of the decision and an order of enforcement.

24.9     SEVERABILITY:

         If any provision in this Agreement is agreed by the Parties to be,
         deemed to be or becomes invalid, illegal, void or unenforceable under
         any law that is applicable hereto, such provision will be deemed
         amended to conform to applicable laws so as to be valid and enforceable
         or, if it cannot be so amended without materially altering the
         intention of the Parties, it will be deleted, with effect from the date
         of such agreement or such earlier date as the Parties may agree, and
         the validity, legality and enforceability of the remaining provisions
         of this Agreement shall not be impaired or affected in any way.

24.10    AMENDMENTS:

         No amendment, modification or addition hereto shall be effective or
         binding on any Party unless set forth in writing and executed by a duly
         authorized representative of all Parties.

24.11    WAIVER:

         No waiver of any right under this Agreement shall be deemed effective
         unless contained in a written document signed by the Party charged with
         such waiver,

<PAGE>

         and no waiver of any breach or failure to perform shall be deemed to
         be a waiver of any future breach or failure to perform or of any
         other right arising under this Agreement.

24.12    ASSIGNMENT:

         None of the Parties shall be permitted to assign its rights or
         obligations hereunder without the prior written consent of the other
         Parties except as follows:

         24.12.1  Elan, EIS and/or Photogen shall have the right to
                  assign their rights and obligations hereunder to their
                  Affiliates provided, however, that such assignment does
                  not result in adverse tax consequences for any other
                  Parties.

         24.12.2  Elan and EIS shall have the right to assign their
                  rights and obligations hereunder to a special purpose
                  financing or similar entity established by Elan or EIS
                  which assignee shall be capable of fulfilling such
                  obligations.

24.13    WHOLE AGREEMENT/NO EFFECT ON OTHER AGREEMENTS:

         This Agreement (including the Schedules attached hereto) and the
         Transaction Documents set forth all of the agreements and
         understandings between the Parties with respect to the subject matter
         hereof, and supersedes and terminates all prior agreements and
         understandings between the Parties with respect to the subject matter
         hereof. There are no agreements or understandings with respect to the
         subject matter hereof, either oral or written, between the Parties
         other than as set forth in this Agreement and the Transaction
         Documents.

         In the event of any ambiguity or conflict arising between the terms of
         this Agreement and those of the Newco Memorandum of Association and
         Bye-Laws, the terms of this Agreement shall prevail.

         No provision of this Agreement shall be construed so as to negate,
         modify or affect in any way the provisions of any other agreement
         between any of the Parties unless specifically referred to, and solely
         to the extent provided herein. In the event of a conflict between the
         provisions of this Agreement and the provisions of the License
         Agreements, the terms of this Agreement shall prevail unless this
         Agreement specifically provide otherwise.

24.14    SUCCESSORS:

<PAGE>

         This Agreement shall be binding upon and inure to the benefit of the
         Parties hereto, their successors and permitted assigns.

<PAGE>

SCHEDULE 1


ELAN LICENSE AGREEMENT

<PAGE>

SCHEDULE 2


PHOTOGEN LICENSE AGREEMENT

<PAGE>

SCHEDULE 3

TECHNOLOGICAL COMPETITORS OF ELAN

[****]

(including any and all divisions or subsidiaries of such entities and
successor entities).

----------------

[****]   REPRESENTS MATERIAL WHICH HAS BEEN REDACTED PURSUANT TO A REQUEST
         FOR CONFIDENTIAL TREATMENT PURSUANT TO RULE 24B-2 UNDER THE
         SECURITIES EXCHANGE ACT OF 1934, AS AMENDED.

<PAGE>

IN WITNESS WHEREOF, the Parties hereto have executed this Agreement on the day
first set forth above.

                                       SIGNED

                                       BY:        /s/ Kevin Insley
                                          --------------------------------
                                       for and on behalf of
                                       ELAN PHARMA INTERNATIONAL LIMITED

in the presence of:
                   ------------------------------


                                       SIGNED

                                       BY:        /s/ Kevin Insley
                                          --------------------------------
                                       for and on behalf of
                                       ELAN INTERNATIONAL SERVICES, LTD.

in the presence of:
                   ------------------------------


                                       SIGNED

                                       BY:        /s/ John Smolik
                                          --------------------------------
                                       for and on behalf of
                                       PHOTOGEN TECHNOLOGIES, INC.
in the presence of:    /s/
                   -----------------------------


                                       SIGNED

                                       BY:        /s/ John Smolik
                                          --------------------------------
                                       for and on behalf of
                                       PHOTOGEN NEWCO LTD.

in the presence of:
                   -----------------------------