<PAGE>

                                                                   Exhibit 10.11

                              EMPLOYMENT AGREEMENT

         THIS EMPLOYMENT AGREEMENT ("AGREEMENT") is made effective as of the
15th day of November, 1999, by and between Photogen, Inc., a Tennessee
corporation ("COMPANY"), and Jay Zimmerman, MEd. ("EMPLOYEE").

                                    RECITALS

         A.       Employee has substantial experience in the conduct of human
clinical trials utilizing images as surrogate endpoints; and

         B. The Company desires to retain Employee and Employee hereby agrees to
serve in such capacity to assist it in various research projects, developing
product inventions and related matters, as hereinafter provided; subject to the
terms of this Agreement.

                                    AGREEMENT

         NOW, THEREFORE, in consideration of the mutual promises herein and for
other good and valuable consideration, the receipt and adequacy of which are
hereby acknowledged, the parties agree as follows:

         1.       DEFINITIONS. The following terms have the meanings set forth
                  below:

         (a)      "COMPANY" means all affiliates of Photogen, Inc., including
                  but not limited to Photogen Technologies, Inc. and Photogen
                  Newco Ltd., except in the context of the entity directly
                  employing Employee which shall mean Photogen, Inc.

         (b)      "COMPETITIVE BUSINESS" means engaging in the research,
                  development, sale, lease, marketing, financing or distribution
                  of technology, products or services similar to or competitive
                  with the Company's products or services in the Field anywhere
                  in the world.

         (c)      "CONFIDENTIALITY AGREEMENT" means that certain Employee
                  Confidentiality and Inventions Agreement of even date herewith
                  between the Employee and the Company attached hereto as
                  Exhibit 4 and incorporated herein in its entirety by
                  reference.

         (d)      "CONFIDENTIAL INFORMATION" has that meaning set forth in the
                  Confidentiality Agreement.

         (e)      "FIELD" means the use of electromagnetic energy (including
                  light generated by ultra fast lasers or other sources, x-rays
                  and other sources of radiation), alone or in combination with
                  photoactive compounds or targeting agents, to treat, diagnose
                  or image human or animal tissue and/or disease.


<PAGE>

         (f)      "PATENTS" means patents, patent applications, and patent
                  disclosures, together with all reissuances, continuations,
                  continuations-in-part, revisions, extensions, and
                  reexaminations thereof, and all improvements and inventions
                  related thereto.

         2.       EMPLOYMENT SERVICES.

         (a)      During the Term of this Agreement, Employee shall use his best
                  efforts to and shall devote 100% of his working time to
                  competently and faithfully promote the Company's interests,
                  develop the Company's products and to perform the following
                  services (collectively, the "EMPLOYMENT SERVICES"):

                  (i) assist the Company's Medical Director to plan, implement
         and complete, the clinical activities for specific research projects
         mutually agreed to between the Company and Employee, including but not
         limited to the following: (A) sentinel lymph node mapping, (B) enhanced
         radiation therapy through the use of radiosensitizers, (C) photodynamic
         therapy of deep tissue cancer, (D) evaluation of hair removal,
         psoriasis, and leg ulcer products; (E) new treatments for Barretts
         esophagus, and (F) other research projects assigned by the Company
         (individually and collectively, "RESEARCH PROJECTS");

                  (ii) plan, implement and complete clinical trial programs
         sufficient to obtain regulatory approval for sentinel node mapping and
         diagnostic products;

                  (iii) negotiate, prepare and monitor clinical contracts;

                  (iv)  lead the implementation of human clinical trials
         undertaken by the Company;

                  (v) assist the Company in obtaining patent or other protection
         for any technologies developed by Employee and arising out of his
         Employment Services ;

                  (vi) assist the Company in obtaining licenses to technologies
         developed by third parties;

                  (vii) assist the Company in working with outside clinical
         researchers and research organizations; and

                  (viii) perform such other duties assigned to Employee from
         time to time by the Company's Medical Director, the Company's Chief
         Executive Officer and/or Board of Directors.

         (b)      Employee will perform the Employment Services substantially in
                  the Boston, Massachusetts area. Employee may also be required
                  to travel from time to time to


                                       -2-

<PAGE>

                  Knoxville, Tennessee and elsewhere as reasonably necessary to
                  perform the Employment Services.

         3.       COMPENSATION.

         (a)      Company shall pay Employee an annual base gross salary as set
                  forth in Exhibit 1, payable in accordance with normal Company
                  payroll procedures and subject to deductions and withholdings
                  required by law or by agreement with Employee. Company will
                  reimburse Employee for reasonable and necessary business
                  expenses in accordance with Company's policies.

         (b)      Concurrently with the execution of this Agreement, Company and
                  Employee will execute an Incentive Stock Option Award
                  Agreement ("Award Agreement") providing for the Company to
                  grant Employee a total of 150,000 options to acquire Company
                  common stock, pursuant to Company's 1998 Long Term Incentive
                  Compensation Plan. The options will vest in accordance with
                  and in all other respects be subject to the provisions of the
                  Award Agreement.

         (c)      Employee will be eligible to participate in and receive
                  benefits provided under Company's insurance and benefit plans
                  as set forth on Exhibit 1, in accordance with their respective
                  provisions. Company reserves the right to amend all insurance
                  and benefit plans at any time as necessary to accomplish
                  Company's business objectives.

         4. COVENANTS AND REPRESENTATIONS. Employee represents and warrants to,
and covenants with, the Company as follows:

         (a)      During the Term, Employee will render services (similar to the
                  Employment Services or otherwise) in the Field only to the
                  Company and will not enter into any other agreement,
                  arrangement, understanding, or other relationship pursuant to
                  which Employee is obligated to render advice and services in
                  the Field to any third party.

         (b)      Employee is under no contractual or other obligation or
                  restriction which is inconsistent with Employee's obligations
                  under this Agreement or the performance of the Employment
                  Services. Employee's pre-existing relationships with
                  commercial, educational or other research institutions are
                  listed in Exhibit 2 attached hereto. Employee will terminate
                  all employment, consulting and similar affiliations with
                  commercial entities in the Field.

         (c)      Employee has set forth on Exhibit 3 attached hereto, a
                  complete list of any patents or patent applications in the
                  Field of which Employee is the joint or sole inventor.


                                       -3-

<PAGE>

         5.       CONFIDENTIALITY.

         (a)      The Company has developed and will develop Confidential
                  Information over a substantial period of time and at
                  substantial expense. The Confidential Information is of great
                  importance to the Company's business. During the Term,
                  Employee may develop, become aware of, or have access to the
                  Confidential Information. In consideration of the foregoing
                  and as an inducement for Company to extend employment to
                  Employee hereunder, Employee has executed the Confidentiality
                  Agreement and Employee acknowledges and agrees the Company is
                  and shall at all times remain the sole owner of the
                  Confidential Information.

         (b)      During the Term and thereafter, Employee shall exercise all
                  commercially reasonable precautions to physically protect the
                  integrity and confidentiality of the Confidential Information.
                  Employee will not remove any Confidential Information or
                  copies thereof from the Company's premises or the other places
                  Employee is authorized to perform the Employment Services to
                  the extent necessary to perform such Employment Services, and
                  then only with the Company's prior written consent.

         (c)      Employee will comply with Company's policies concerning
                  publication with respect to his work for the Company.

         6.       NONCOMPETITION; NONSOLICITATION.

         (a)      During the Term, and for 12 months after termination of the
                  Term, the Employee agrees not to, directly or indirectly
                  through any other person or entity, (i) own, manage, control,
                  participate in, consult with, be employed by, render services
                  for, any person or entity engaged in a Competitive Business or
                  in any manner or in any capacity (except as owner of 2% or
                  less of stock of a publicly registered and traded entity)
                  engage in any Competitive Business, (ii) solicit, induce or
                  attempt to influence any other person or entity to engage in
                  any Competitive Business or to curtail or cease any business
                  or business relationship with the Company, its affiliates,
                  employees or independent contractors, (iii) solicit any other
                  employee or independent contractor to terminate any employment
                  or engagement with the Company and engage in a Competitive
                  Business, or (iv) disparage the Company, its affiliates,
                  employees, independent contractors or their services or
                  products.

         (b)      The Company consents to Employee performing services for the
                  entities listed in paragraph 4(b), provided that (i) Employee
                  keeps the Company advised on a current basis of his activities
                  for such other entities (or, to the extent Employee is unable
                  to keep the Company advised because of a confidentiality
                  agreement with such other entity, Employee will disclose as
                  much information as possible without


                                       -4-

<PAGE>

                  breaching the confidentiality agreement and seek the other
                  entity's permission to make further limited disclosure to the
                  Company), (ii) Employee strictly observes the confidentiality
                  obligations in paragraph 7, above, and (iii) Employee uses his
                  best efforts to assure that those other entities do not obtain
                  any interest in Developments or the Company's Patents. Upon
                  written notice by one party hereto to the other of a conflict
                  situation, Employee and the Company will negotiate in good
                  faith for a period of 30 days (or longer by mutual agreement)
                  to modify Employee's responsibilities under this Agreement or
                  to develop other protections and procedures to minimize the
                  possibility of competitive conflict, the disclosure of
                  Confidential Information and uncertainty as to the Company's
                  ownership of Developments or the Company's Patents. If
                  Employee and the Company are unable to agree on such
                  modifications, either of them may terminate this Agreement
                  upon written notice to the other.

         7.       TERM AND TERMINATION.

         (a)      Unless terminated earlier pursuant to paragraph 7(b) below,
                  this Agreement shall be in effect for an initial term of four
                  years beginning on the effective date hereof (the "INITIAL
                  TERM"). This Agreement may be renewed for successive renewal
                  terms lasting for one year (the "RENEWAL TERMS") upon mutual
                  written agreement of the parties. The Initial Term and any
                  subsequent Renewal Terms are collectively referred to as the
                  "TERM."

         (b)      This Agreement and Employee's employment by the Company may be
                  terminated before the expiration of any Term as follows:

                  (i)      By the Company in the event:

                           (1)      Employee commits a material breach of this
                                    Agreement where such breach, if curable, is
                                    not remedied to the Company's reasonable
                                    satisfaction within thirty (30) days after
                                    written notice to Employee (and termination
                                    shall be effective as of the end of such
                                    30-day period); or

                           (2)      Employee is convicted for committing an act
                                    of fraud, embezzlement, theft or another act
                                    constituting a felony (and termination shall
                                    be effective upon written notice to
                                    Employee); or

                           (3)      Employee dies or becomes mentally or
                                    physically disabled such that the Employee
                                    cannot, in the opinion of an independent
                                    physician selected by the Company, perform
                                    the Employment Services (with reasonable
                                    accommodation to the extent required by law)
                                    for a period of 12 months (and termination
                                    shall be effective


                                       -5-

<PAGE>

                                    on the date Employee dies or upon written
                                    notice the Company has determined he is
                                    disabled under the foregoing criteria);

                           in which case: (A) the Company shall pay Employee his
                           base salary and any other amounts required by
                           applicable law to be paid through the effective date
                           of termination but the Company shall have no other
                           obligations under this Agreement as of the effective
                           date of the termination, and (B) the Company shall
                           permit the Employee or his beneficiary to exercise
                           vested options to acquire Company stock in accordance
                           with and subject to the Award Agreement.

                  (ii) By the Company in the event the Company is dissatisfied
         in its reasonable judgment with the Employee's performance of the
         Employment Services or the results thereof which, if curable, are not
         remedied to the Company's reasonable satisfaction within forty-five
         (45) days after specific written notice thereof has been delivered to
         the Employee (and termination shall be effective as of the end of such
         45-day period); in which case: (A) the Company shall pay Employee his
         base salary and any other amounts required by applicable law to be paid
         through the effective date of termination but the Company shall have no
         other obligations under this Agreement as of the effective date of the
         termination, and (B) the Company shall permit the Employee or his
         beneficiary to exercise vested options to acquire Company stock in
         accordance with and subject to the Award Agreement.

                  (iii) By the Employee, provided the Employee shall give the
         Company at least 60 days prior written notice thereof (and termination
         shall be effective as of the end of such 60-day or longer period); in
         which case (A) the Company shall pay Employee his base salary and any
         other amounts required by applicable law to be paid through the
         effective date of termination but the Company shall have no other
         obligations under this Agreement as of the effective date of the
         termination, and (B) the Company shall permit the Employee to exercise
         vested options to acquire Company stock in accordance with and subject
         to the Award Agreement.

         (c)      Notwithstanding anything to the contrary, the obligations
                  under this Agreement which by their terms survive termination,
                  including, without limitation, the applicable Confidentiality,
                  Noncompetition, and Nonsolicitation provisions of this
                  Agreement as set forth in paragraphs 5 and 6 hereof and the
                  Confidentiality Agreement, shall survive termination; and the
                  representations and warranties, including without limitation
                  the provisions of paragraph hereof, shall survive termination.
                  Upon termination, and in any case upon the Company's request,
                  Employee shall return immediately to the Company all
                  Confidential Information and copies thereof and not retain any
                  copies thereof.


                                       -6-

<PAGE>

         8.       MISCELLANEOUS.

         (a)      This Agreement and the rights and obligations hereunder may
                  not be assigned, delegated or transferred by Employee without
                  the prior written consent of the Company. The Company may
                  assign this Agreement to an affiliate of the Company or to an
                  acquirer or successor in connection with the merger,
                  consolidation, or sale of all or substantially all of its
                  assets, and this Agreement shall inure to the benefit of the
                  Company's assignee.

         (b)      This Agreement may not be amended or modified, or any
                  provision hereof waived, except by a written instrument duly
                  signed by both parties contemporaneously or after the date of
                  this Agreement. This Agreement (together with the Award
                  Agreement and the Agreement regarding certain conditions)
                  constitutes the entire agreement between the parties
                  concerning the subject matter hereof and thereof, and
                  supersedes all prior written or oral negotiations,
                  representations and agreements.

         (c)      The Employee acknowledges that a breach of paragraphs 5, 6 or
                  the Confidentiality Agreement may cause the Company and its
                  affiliates irreparable harm. Accordingly, in the event of a
                  breach or threatened breach by the Employee of any of the
                  provisions of paragraphs 5, 6 or the Confidentiality
                  Agreement, the Employee agrees that the Company may be
                  entitled to injunctive relief restraining the Employee and any
                  individual or entity from participating in such breach or
                  threatened breach. The Employee waives any provision of law
                  requiring the Company to post a bond for any such injunctive
                  relief. Nothing herein shall be construed as prohibiting the
                  Company from pursuing any other remedies available at law or
                  in equity for any breach or threatened breach of this
                  Agreement.

         (d)      Any waiver of a breach of any provision of this Agreement
                  shall not operate as a waiver of any other breach of such
                  provision or any other provision, nor shall any failure to
                  enforce any provision hereof operate as a waiver of such
                  provision or of any other provision.

         (e)      If any provision of this Agreement is deemed in a final order
                  by a court of competent jurisdiction to be unenforceable or
                  invalid, the enforceability and validity of all other
                  provisions shall not be affected and that court shall modify
                  the unenforceable or invalid provision to the extent necessary
                  to render it enforceable and valid and that provision shall be
                  enforced as modified. Employee agrees that the time period and
                  scope of the covenants in paragraphs 6, 7 and 8 of this
                  Agreement are reasonable and appropriate under the
                  circumstances of the Company's business.


                                       -7-

<PAGE>

                  IN WITNESS WHEREOF, Employee and the President of the Company
have signed this Agreement as of the Effective Date.

COMPANY                                   EMPLOYEE

Photogen, Inc.

By:     /S/ JOHN T. SMOLIK                  By:         /S/ JAY ZIMMERMAN
         John T. Smolik, President                       Jay Zimmerman, MEd.

Address: 7327 Oak Ridge Highway             Address:      165 Codman Hill Rd.
         Suite B                                          Harvard, MA  01451
         Knoxville, TN  37931
         Telephone:    423/769-4011                  Telephone:_______________
         Telecopier:   423/769-4013                  Telecopier:______________
         E-mail:       smolik@photogen.com           E-mail: _________________



                                       -8-
<PAGE>

                                    EXHIBIT 1

                             TITLE AND COMPENSATION

Title:            Vice President of Clinical Operations

Gross Salary:     Starting salary of $125,000 per year.  Salary subject
                  to periodic review.

Bonus/Options:    Bonus will be available and paid at the discretion
                  of the Board or its Compensation Committee.

Benefits:         Medical/Dental/Term Life Insurance
                  Long term disability insurance
                  Paid vacation (4 weeks, 9 Company holidays and 2
                  floating days)
                  Benefit programs will be developed and
                  implemented as approved by the Board 401(k) salary
                  deferral plan (non-contributory by Company


<PAGE>

                                    EXHIBIT 2

                      EMPLOYEE'S PREEXISTING RELATIONSHIPS

<TABLE>
<CAPTION>
                                                      SUBJECT TO WRITTEN
                                                          AGREEMENT
                                                           (Y OR N)
                                                      IF "YES" ATTACH A
ENTITY             SUMMARY OF RELATIONSHIP            COPY OF AGREEMENT
                                                         (REDACTED AS
                                                           NECESSARY)
<S>               <C>                                 <C>
------------------------------------------------------------------------------
NF Foundation     Board Member                                  N
------------------------------------------------------------------------------
WorldCare Inc.    Past COO                                      N
------------------------------------------------------------------------------

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

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

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

------------------------------------------------------------------------------
</TABLE>


                                       -1-
<PAGE>

                                    EXHIBIT 3

                        EMPLOYEE'S INTELLECTUAL PROPERTY

<TABLE>
<CAPTION>

DESCRIPTION                                            STATUS
<S>                                              <C>
------------------------------------------------------------------------------
[List any patents or patent applications]

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

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

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

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

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

------------------------------------------------------------------------------
</TABLE>

<PAGE>

                                    EXHIBIT 4

         See attached Employee Confidentiality and Inventions Agreement.

<PAGE>

                       [PHOTOGEN TECHNOLOGIES, INC. LETTERHEAD]

                                November 15, 1999

Mr. Jay Zimmerman, Ph.D
165 Codman Hill Rd.
Harvard, MA  01451

       RE: EMPLOYEE CONFIDENTIALITY AND INVENTIONS AGREEMENT ("AGREEMENT")

Dear Mr. Zimmerman:

                  In the course of your work for Photogen, Inc., its parent
company Photogen Technologies, Inc. or any of their affiliates (collectively,
"Photogen"), you may have access to Photogen's confidential and proprietary
information and/or you may create Developments (defined below). As a condition
to Photogen hiring and employing you (and for other legally sufficient
consideration, the receipt and adequacy of which you acknowledge), you and
Photogen agree as follows:

         1.       CONFIDENTIAL INFORMATION.

         (a)      During your employment by Photogen and for a period of three
                  (3) years following termination of your employment, for any
                  reason, you will hold in trust, keep confidential and not
                  disclose, directly or indirectly, to any third parties or make
                  any use of Confidential Information (defined below) for any
                  purpose except for the benefit of Photogen in the performance
                  of your duties. Confidential Information will not be subject
                  to these restrictions if it becomes generally known to the
                  public or in the industry without any fault by you or any
                  other person or entity, or if Photogen ceases to have a
                  legally protectable interest in it. Upon termination of your
                  employment (regardless of the reason for termination), you
                  will immediately return to Photogen all tangible Confidential
                  Information and any other material made or derived from
                  Confidential Information, including information stored in
                  electronic format and handwritten notes, which is in your
                  possession or which you delivered to others.

         (b)      "Confidential Information" means any and all information that
                  has or could have value or utility to Photogen, whether or not
                  reduced to written or other tangible form and all copies
                  thereof, relating to Photogen's private or proprietary
                  matters,


<PAGE>

[LOGO]

Jay Zimmerman, Ph.D.
November 15, 1999
Page 2

                  confidential matters or trade secrets. Confidential
                  Information includes, but is not limited to, the following:

                  (i) technical information (whether or not subject to patent
         registration or protection), such as research and development, methods,
         trade secrets, know-how, formulas, compositions, protocols, processes
         and techniques, discoveries, machines, inventions, ideas, computer
         programs (including software and data used in all such programs),
         drawings, specifications;

                  (ii) except to the extent publicly disclosed by Photogen
         without any fault by you or any other person or entity, information
         relating to Photogen's patents, patent applications, and patent
         disclosures, together with all reissuances, continuations,
         continuations-in-part, revisions, extensions, and reexaminations
         thereof, and all improvements and inventions related thereto;

                  (iii) business information, such as information concerning any
         products, customers, suppliers, production, developments, costs,
         purchasing, pricing, profits, markets, sales, accounts, customers,
         financing, acquisitions, strategic alliances or collaborations,
         expansions; and

                  (iv) other information relating to Photogen's business
         practices, strategies or policies which are deemed a "trade secret"
         under applicable laws.

         2.       DEVELOPMENTS.

         (a)      You agree to promptly and fully disclose in writing to
                  Photogen, Inc.'s President all Developments that are related
                  to or useful in the business or demonstrably anticipated
                  business of Photogen, or result from duties assigned to you by
                  Photogen or from the use of any of Photogen's assets or
                  facilities. "Developments" means any and all inventions,
                  discoveries, improvements, know- how, works or other
                  intellectual property (whether or not subject to registration
                  with any governmental office) you conceive, reduce to
                  practice, discover or make, alone or with others, during your
                  employment and for twelve (12) months after termination
                  (regardless of the reason for termination).

         (b)      You hereby assign and transfer to Photogen, Inc. all of your
                  right, title and interest in and to all Developments. You
                  agree to sign and deliver to Photogen, Inc. (during and after
                  employment) other documents Photogen, Inc. considers


<PAGE>

[LOGO]

Jay Zimmerman, Ph.D.
November 15, 1999
Page 3

                  necessary or desirable to evidence its ownership of
                  Developments. All copyrightable works that are Developments,
                  whether or not works made for hire (as defined in 17 U.S.C.
                  Section 101), shall be owned by Photogen, Inc. and it may file
                  and own the same as the author throughout the world. If
                  Photogen, Inc. is unable for any reason to secure your
                  signature on any document necessary or desirable to apply for,
                  prosecute, obtain, or enforce any patent, trademark, service
                  mark, copyright, or other right or protection relating to any
                  Development, you hereby irrevocably designate and appoint
                  Photogen, Inc. and each of its duly authorized officers and
                  agents, as your agent and attorney-in-fact to act for and in
                  your behalf and stead to execute and file any such document
                  and to do all other lawfully permitted acts to further the
                  prosecution, issuance, and enforcement of patents, trademarks,
                  service marks, copyrights, or other rights or protections with
                  the same force and effect as if personally executed and
                  delivered by you. You agree that this power of attorney is
                  irrevocable and is coupled with an interest and thereby
                  survives your death or disability.

         3. NO CONFLICTS. You represent and warrant to, and agree with Photogen
that:

         (a)      You are under no contractual or other obligation or
                  restriction which is inconsistent with your obligations under
                  this Agreement or the performance of you duties for Photogen.
                  Without limiting the generality of the foregoing, performing
                  your duties for Photogen will not cause you to breach any
                  agreement or other duty which obligates you to keep in
                  confidence any confidential or proprietary information or
                  trade secret of any third party or to refrain from competing,
                  directly or indirectly, with the business of any third party.

         (b)      Neither you nor any third party has any ownership or other
                  interest in any idea, invention or other item of intellectual
                  property that will be used in performing your duties for
                  Photogen, and all Developments will be free and clear of any
                  encumbrances or claims of third parties. In performing your
                  duties for Photogen, you will not disclose to Photogen or use
                  any confidential or proprietary information or trade secret of
                  any third party, and you will not interfere with the business
                  of any third party in any way contrary to applicable law.

         (c)      In performing your duties for Photogen, you will comply with
                  applicable laws and regulations.


<PAGE>

[LOGO]

Jay Zimmerman, Ph.D.
November 15, 1999
Page 4

         4. NO EMPLOYMENT RIGHTS. Nothing in this Agreement shall affect your or
Photogen's right to terminate your employment or Photogen's right modify your
terms of employment, or to confer on you any other rights or benefits in
connection with your employment.

         5. SEVERABILITY; CHOICE OF LAW; INJUNCTION. If any provision of this
Agreement is deemed by a court of competent jurisdiction to be unenforceable or
invalid, the enforceability and validity of all other provisions shall not be
affected and that court shall modify the unenforceable or invalid provision to
the extent necessary to render it enforceable and valid and that provision shall
be enforced as modified. You agree that the time period and scope of the
covenants in this Agreement are reasonable and appropriate under the
circumstances of Photogen's business. This Agreement shall be governed and
interpreted in accordance with the laws of the State of Tennessee without regard
to its provisions on conflicts of law. Without limiting any other available
remedies at law or in equity, Photogen will be entitled to injunctive relief
restraining any individual or entity from participating in any breach or
threatened breach of this Agreement without having to post a bond or security.

         6. MISCELLANEOUS. This Agreement may not be amended or modified except
by a written instrument signed by both parties after the date of this Agreement.
This Agreement may be assigned by Photogen and shall inure to the benefit of
Photogen, its successors and assigns, but may not be assigned or delegated by
you. This Agreement supersedes all prior agreements, negotiations and
representations, written or oral, between the parties with respect to the
subject matter contained herein. Any waiver of any breach of, or failure to
enforce, any of the provisions of this Agreement shall not operate as a waiver
of any other breach or waiver of performance of such provisions or any other
provisions. Your obligations under this Agreement survive termination of your
employment, regardless of the manner or reason for termination.


<PAGE>

[LOGO]

Jay Zimmerman, Ph.D.
November 15, 1999
Page 5

                  Please indicate your agreement to the foregoing by signing a
copy of this letter below and returning it to me. I look forward to working with
you.

                                               Very truly yours,

                                               /s/ John Smolik

                                               John T. Smolik, President

Accepted and Agreed to as of
November 15, 1999.



By:  /S/ JAY ZIMMERMAN
   -------------------------
     Jay Zimmerman, MEd.