EXHIBIT 10.22

                            JOINT VENTURE AGREEMENT


                        DATED AS OF NOVEMBER 30, 1995 

                      [*Confidential Treatment Requested]

 
                               TABLE OF CONTENTS

                                                                            PAGE
1.   Definitions.                                                              1
      1.1   "Affiliate".....................................................   1
      1.2   "Board of Managers" or "Board"..................................   1
      1.3   "Diagnostic Field"..............................................   1
      1.4   "Voting Interest"...............................................   1
      1.5   "Person"........................................................   2
      1.6   "MSD Products"..................................................   2
      1.7   "MST/MSD License"...............................................   2
      1.8   "Licensed Technology"...........................................   2
      1.9   "Member" or "Members"...........................................   2
     1.10   "Net Sales".....................................................   2
     1.11   "Research Technologies".........................................   2
     1.12   "ECL Improvements"..............................................   2
     1.13   "MSD Improvements"..............................................   2
     1.14   "Scientific Advisory Board".....................................   3

2.   Organization and Capitalization of MSD.................................   3
     2.1   LLC Agreement: Certificate of Formation..........................   3
     2.2   Board of Managers................................................   3
     2.3   Technology Contributions.........................................   4
     2.4   IGEN Financing...................................................   4
     2.5   Additional Funding If Product Developed..........................   5
     2.6   Distributions....................................................   5
     2.7   Restrictions on MSD..............................................   6
     2.8   Budget...........................................................   6

3.   Operation of MSD.......................................................   6
      3.1   Business of the Joint Venture...................................   6
      3.2   Place of Business...............................................   7
      3.3   Operating Plan..................................................   7
      3.4   Fiscal Year.....................................................   7
      3.5   Facilities......................................................   7
      3.7   Other Services and Support......................................   8
      3.8   Distribution....................................................   9
      3.9   Publication Control.............................................   9
     3.10   Intellectual Exchange...........................................   9
     3.11   Employment of Wohlstadter.......................................   9

4.   Future Developments: Competition: Licenses.............................  10
     4.1   Exclusive Vehicle................................................  10
     4.2   IGEN Developments................................................  11

                                      i.

 
                               TABLE OF CONTENTS
                                  (continued)
                                                                           PAGE

     4.3   MSD Developments.................................................  11
     4.4   Right of Negotiation.............................................  11

5.   Confidentiality........................................................  11
     5.1   Confidential Information.........................................  11
     5.2   Term of Confidentiality..........................................  12
     5.3   Use of Confidential Information..................................  12
     5.4   Exceptions.......................................................  12
     5.5   MST Publication Rights...........................................  12

6.   Rights and Obligations Regarding MSD Membership Interests..............  13
     6.1   Restriction on Resale............................................  13

7.   Dispute Resolution.....................................................  13
     7.1   Business Decisions and Disagreements.............................  13
     7.2   Disputes concerning Contractual Obligations......................  13

8.   Term and Termination...................................................  14
     8.1   Term.............................................................  14
     8.2   Extension of Term................................................  14
     8.3   Termination by Agreement.........................................  14
     8.4   Termination for Breach...........................................  14
     8.5   Consequences of Termination......................................  14

9.   Representations........................................................  15
     9.1   Authorization....................................................  15
     9.2   No Breach........................................................  15

10.  Miscellaneous Provisions...............................................  16

                                      ii.

 
                            JOINT VENTURE AGREEMENT


     The parties to this Agreement dated as of November 30, 1995 are MESO SCALE
DIAGNOSTICS, LLC. ("MSD"), a Delaware limited liability company, MESO SCALE
TECHNOLOGIES, LLC. ("MST"), a Delaware limited liability company, and IGEN, INC.
("IGEN"), a California corporation.

                                    RECITALS

     MST and IGEN have jointly prepared a Research Outline for a program of
research and development (the "Research Program") to be conducted by MSD.  The
Research Outline is attached hereto as Exhibit A.  IGEN and MST have caused MSD
to be organized for the purpose of conducting this research and development and,
if successful, developing, manufacturing, marketing and selling products,
processes and services based thereon.  MST wishes to license MSD to develop and
sell commercial products and services based on technology for certain
applications.  IGEN wishes to provide initial financing and facilities to MSD,
and provide the services of certain personnel.  The parties are entering into
this Joint Venture Agreement to set forth their respective rights and
obligations in this endeavor.

1.   DEFINITIONS.

     As used in this Agreement, the following terms shall have the meanings
defined below:

     1.1 "AFFILIATE" shall mean, with respect to any Person, any Person directly
or indirectly controlling or controlled by or under direct or indirect common
control with such Person. For purposes of this definition, "control" when used
with respect to any Person means the possession, direct or indirect, of the
power to direct, or cause the direction of, the management and policies of such
Person, whether through the ownership of voting securities, by contract or
otherwise, and the terms "controlling" and "controlled" have meanings
correlative to the foregoing.

     1.2 "BOARD OF MANAGERS" or "BOARD" shall mean the Board of Managers of MSD.

     1.3 "DIAGNOSTIC FIELD" shall mean all diagnostic devices and procedures for
the quantification or detection of predetermined or known analytes, including,
without limitation, immunoassays and procedures utilizing nucleic acid probes,
for human clinical research, environmental, agricultural, veterinary, food
testing, industrial and similar purposes, but excluding any territories,
segments, devices, procedures or applications to the extent, and so 

                                      1.

 
long as, IGEN has exclusively granted licenses to third parties under technology
owned by or licensed to IGEN in any such territory, segment, device, procedure
or application.

     1.4 "VOTING INTEREST" shall mean any interests in MSD that entitle the
holder thereof to vote as a Member of MSD, and any security convertible into or
exchangeable therefor.
 
     1.5 "PERSON" shall mean any individual, decedent's estate, corporation,
partnership, limited liability company, joint venture, association, joint-stock
company, trust, unincorporated organization or government or any agency or
political subdivision thereof.

     1.6 "MSD PRODUCTS" shall mean any products containing or utilizing any MSD
Improvements or ECL Improvements developed by MSD.

     1.7 "MST/MSD LICENSE" shall mean the license agreement attached hereto as
Exhibit D.

     1.8 "LICENSED TECHNOLOGY" shall mean the technology licensed to MSD
pursuant to the MST/MSD License.

     1.9 "MEMBER" or "MEMBERS" shall mean each of the parties of this Agreement,
or the parties as a group, other than MSD.

     1.10 "NET SALES" shall mean, for any period, the invoiced sales price
charged for all MSD Products commercially sold by IGEN in such period, less (i)
trade, cash and quantity discounts or rebates actually taken or allowed; (ii)
credits or allowances given or made for rejected, damaged or returned goods,
(iii) uncollectible amounts on MSD Products previously sold, (iv) retroactive
price reductions and (v) any freight or insurance charges billed to the
customer.

     1.11 "RESEARCH TECHNOLOGIES" shall mean (i) [ * ] methods, including,
without limitation, the [ * ] described in the United States Patent application
entitled [ * ] serial no. [ * ] (including all divisions, continuations and
continuations-in-part thereto), and [ * ] (ii) [ * ] and [ * ] the [ * ] and/or
[ * ] (e.g., through [ * ] and [ * ] and [ * ] (e.g., through [ * ] and [ * ]
and (iii) [ * ] (e.g., [ * ] "Research Technologies" specifically include, but
are not limited to, [ * ] (e.g., [ * ] and/or [ * ] and [ * ] with [ * ] and/or
[ * ] as well as the use of [ * ] and/or [ * ] of an [ * ] in the [ * ] (e.g.,
[ * ]
                                      2.
                                                                                
                                                      [* Confidential treatment]

 
     1.12 "ECL IMPROVEMENTS" shall mean electrochemiluminescent labels, general
electro-chemical techniques and processes for modulating electric potential to
alter chemical species for use in single electrode systems (i.e., for serial
detection using flow cells )

     1.13 "MSD IMPROVEMENTS" shall mean any inventions or know-how developed by
MSD based on any IGEN Confidential Information.
 
     1.14 "SCIENTIFIC ADVISORY BOARD" shall mean the committee of scientific
advisors with appropriate expertise in the Diagnostic Field and Research
Technologies to be designated by the Board of Managers of MSD.

2.   ORGANIZATION AND CAPITALIZATION OF MSD.

     2.1   LLC AGREEMENT: CERTIFICATE OF FORMATION.  The Limited Liability
Company Agreement (the "LLC Agreement") of MSD and the Certificate of Formation
(the "Certificate") of MSD are attached as Exhibits B and C hereto,
respectively.

     2.2   BOARD OF MANAGERS.  For so long as this Agreement remains in effect,
the Board of Managers of MSD shall consist of two persons, one of whom shall be
designated by MST, and one of whom shall be designated by IGEN.  MSD and each
Member (for so long as such Member owns a Voting Interest in MSD) shall take or
cause to be taken all such action (including, but not limited to, the voting of
Voting Interests in MSD held by the Members (or the taking of action by consent
with respect to such interests)) as may be required, from and after the date
hereof:

          2.2.1 to establish and maintain the authorized size of the Board of
Managers of MSD at two managers; to maintain the quorum requirements for actions
of the Board of Managers at two managers; and to maintain the voting
requirements for actions of the Board of Managers of MSD at a majority of
Managers present at a meeting at which there is a quorum, except as provided
otherwise in Section 2.2.6 hereof;

          2.2.2 so long as IGEN or any direct or indirect wholly-owned
subsidiary holds any Voting Interest in MSD, to cause to be elected to the Board
of Managers a designee of IGEN (the "IGEN Manager");

          2.2.3 so long as MST or any Affiliate holds any Voting Interest in
MSD, to cause to be elected to the Board of Managers a designee of MST (the "MST
Manager") ;

          2.2.4 to remove forthwith any IGEN Manager when and only when such
removal is requested by IGEN; to remove forthwith any MST Manager when and only

                                      3.

 
when such removal is requested by MST, provided that the parties hereto have no
right to remove any MST Manager or any IGEN Manager from the Board of Managers
of MSD other than as set forth in this Section 2.2.4;

          2.2.5 in the case of death, resignation or removal as herein provided
of such a manager of MSD, to elect (only in accordance with the procedures set
forth in Sections 2.2.2, 2.2.3 and 2.2.4 above, and subject to Section 5.1.3 of
the LLC Agreement) another manager nominated by MST or IGEN, depending upon
which party designated the deceased, resigning or removed manager;

          2.2.6 to use reasonable efforts to prevent any action from being taken
by the Board of Managers of MSD during the pendency of any vacancy due to death,
resignation or removal of a manager, unless the party entitled to nominate a
person to be elected to fill such vacancy shall have failed for a period of at
least 20 days after notice of such vacancy to nominate such person; provided,
however, that this Section 2.2.6 shall not apply to circumstances in which
action must be taken by the Board of Managers to protect the rights and assets
of MSD;

          2.2.7 to cause the Board of Managers of MSD to meet at least quarterly
during the term of this Agreement; and

          2.2.8 to cause the LLC Agreement and the Certificate to be amended to
the extent necessary to conform to, and to be consistent with, any amendments
made to this Agreement.

     2.3   TECHNOLOGY CONTRIBUTIONS.  Promptly following the execution of this
Agreement, MST and MSD shall execute the MST/MSD License as a capital
contribution of property to MSD.  In consideration for the MST/MSD License, MST
shall become a Class A Member of MSD.

     2.4   IGEN FINANCING.

          2.4.1   INITIAL IGEN CAPITAL CONTRIBUTION.  IGEN shall fund the
operations of MSD by making an initial capital contribution to MSD of $5,000,000
(the "Initial IGEN Capital Contribution").  The Initial IGEN Capital
Contribution shall be divided into two contributions: (i) the Initial IGEN Class
A Capital Contribution, and (ii) the Initial IGEN Class B Capital Contribution.

          (a) The Initial IGEN Capital Contribution shall be contributed by IGEN
to MSD over time, on a quarterly basis (in advance), in accordance with the
budget approved by the Board of Managers from time to time pursuant to Section
2.8 hereof.  For purposes of determining the amount to be contributed, the
budget shall be rounded up to the nearest $500 increment.  After approval by the
Board of Managers, MSD may require IGEN to accelerate 

                                      4.

 
the Initial IGEN Capital Contribution in amounts in excess of such budget by
giving IGEN three business days notice. In the event the Board of Managers has
not approved a budget for a given quarter, IGEN shall contribute to MSD at the
beginning of such quarter an amount equal to the greater of (i) the amount set
forth in the most recently approved earlier budget, or (ii) the quotient
obtained by dividing (x) the amount of the Initial IGEN Capital Contribution not
previously contributed to MSD pursuant to this Section 2.4.1 by (y) the number
of quarters remaining in the initial five (5) year term of this Agreement. In
the event of a change of control of 30% or more of the voting capital stock of
IGEN from the date hereof, or if Richard Massey ceases to be IGEN's
representative on the Board of Managers of MSD, IGEN shall promptly pay to MSD
any amount of the Initial IGEN Capital Contribution not previously paid to MSD.

          (b) For each $500 of the Initial IGEN Capital Contribution
contributed, $1.00 shall be credited to IGEN's Class A Capital Account (the
"Initial Class A Capital Contribution") and $499.00 shall be credited to IGEN's
Class B Capital Account (the "Initial IGEN Class B Capital Contribution"). As of
any date, IGEN's Class A membership interest shall be the quotient, expressed as
a percentage, obtained by dividing the amount of the Initial IGEN Class A
Capital Contribution credited to IGEN's Class A Capital Account as of such date
by 20,000, and MST's Class A membership interest as of any date shall be the
difference between such quotient, expressed as a percentage, and 100 percent
(each, a "Percentage Interest"). Upon contribution of all of the Initial IGEN
Capital Contribution, the Percentage Interest of each Member shall be 50%.

          (c) Notwithstanding any other provision in this Agreement, IGEN may,
upon written notice to MST, contribute the remaining portion of the Initial IGEN
Capital Contribution.

          2.4.2  ORGANIZATIONAL AND START-UP CAPITAL EXPENSES.  IGEN shall fund
the organizational and ongoing operating (non-Research Program) expenses of MSD
(and, to the extent incurred in connection with services rendered on behalf of
MSD, such expenses of any subcontractor of MSD retained by MSD pursuant to
Section 3.1 hereof), including reasonable travel and legal expenses, and startup
capital expenses (including without limitation, the capital expenditures set
forth on Schedule 2.4.2), all such expenses and expenditures to be subject to
approval by the Board of Managers.  Such amounts shall be funded by IGEN
promptly upon the request of the Board of Managers.  Such funding shall be
treated as Class C capital contributions to MSD in exchange for IGEN becoming a
Class C Member of MSD.

     2.5   ADDITIONAL FUNDING IF PRODUCT DEVELOPED.  If MSD has developed a
product prior to the expiration of the term of this Agreement or any extended
term, then MSD shall from time to time prepare and submit to IGEN plans for the
funding required to cover all costs of testing, manufacturing and marketing such
product, including all approvals, and the operating expenses of MSD.  MSD shall
have the right to continue to seek funding from IGEN until such time as MSD
shall have positive net income for two consecutive fiscal quarters as a result

                                      5.

 
of the sale or license of such product.  IGEN shall, within 45 days of its
receipt of each such plan, notify MSD as to whether IGEN agrees to provide funds
in accordance with such plan.  Such funding shall be treated as additional Class
C capital contributions to MSD.  In the event IGEN elects not to provide such
funding, IGEN, MST and MSD shall work in good faith and use reasonable efforts
to secure funding for such plan from third parties.  If a definitive agreement
regarding such funding has not been executed within 180 days after IGEN's
receipt of such plan, MST shall have the right to terminate this Agreement and
MSD and MST shall have the rights set forth in Section 8.5.3 hereto.

          2.5.1   DEVELOPED PRODUCT. For the purposes of this Agreement, a
product shall be deemed to have been developed if (i) it is submitted for FDA
approval, (ii) it is declared developed by the Board of Managers, or (iii) it
has been developed sufficiently to be submitted for FDA approval,
notwithstanding failure of MSD to do so.

     2.6   DISTRIBUTIONS.  Except for distributions made in accordance with the
LLC Agreement, MSD shall not make any distributions to its members without the
unanimous consent of the Members.
 
     2.7  RESTRICTIONS ON MSD.

          2.7.1   During the term of this Agreement, MSD shall not, without the
unanimous consent of the Members:

               (a) Issue any Voting Interest or admit any members;

               (b) Enter into any agreement with, make any payment to, or 
engage in any transaction with IGEN or MST, other than those expressly provided
for herein; or

               (c) Amend or repeal any provision of, or add any provision to the
LLC Agreement or the Certificate.

          2.7.2  MSD will not grant any sublicense on the License Technology (as
defined in the MST/MSD License) or under the MST/MSD License without the prior
written consent of MST in each case, which consent may be withheld by MST in
each case in its sole discretion.  A breach by MSD of this provision stall
entitle MST to terminate the MST/MSD License upon notice by MST to MSD.  If MST
terminates the MST/MSD License due to a breach by MSD of this Section 2.7.2, the
license granted pursuant to the MST/MSD License shall terminate immediately.

     2.8   BUDGET.  Prior to the beginning of each fiscal year, the management
of MSD shall prepare and submit to the Board of Managers a budget for that
fiscal year, which budget shall be subject to unanimous approval of the Board of
Managers. For each calendar quarter, 

                                      6.

 
management shall submit a revised budget for the balance of such year, which
revised budget shall also be subject to unanimous approval of the Board of
Managers. Any changes to an approved budget, and any expenditures outside of the
budget, must be approved in each case by unanimous vote of the Board of
Managers. If the Board of Managers shall fail to approve a budget, the most
recently approved earlier budget shall remain in effect until the Board of
Managers approves a new budget.

3.   OPERATION OF MSD.

     3.1   BUSINESS OF THE JOINT VENTURE.  The business of MSD shall be limited
to the following:

          (i) to perform the obligations and exercise the rights of MSD under
the Research Program;

          (ii) to conduct research and development for the purpose of developing
products, processes and services utilizing the results of the Research Program
in the Diagnostic Field; and
 
          (iii) to manufacture, market, and sell such products, processes and
services in the Diagnostic Field, including, without limitation, the operation
of businesses performing services utilizing the products and processes
developed, and the storage and sale of information obtained from the provision
of such services.

MSD shall engage in no other business without the written consent of both of the
Members.  MSD may contract with third parties for the performance of one or more
of MSD's obligations under this Agreement, including without limitation, the
conduct of the Research Program.  Such third parties, may, but need not be,
Affiliates of a Member, provided that any such agreement with an Affiliate of a
Member must be approved by unanimous consent of the Board of Managers.  In the
event such a third party shall develop a product for MSD, MSD shall be deemed to
have developed such product for purposes of this Agreement.

     3.2   PLACE OF BUSINESS.  The principal place of business of MSD shall
initially be located in Gaithersburg, Maryland at IGEN's facility.  The Board of
Managers may, at any time and from time to time, change the location of MSD's
principal place of business or establish such additional place or places of
business as the Board of Managers may from time to time deem appropriate.

     3.3   OPERATING PLAN.  Promptly following commencement of the Research
Program, and each year thereafter, the Board of Managers shall formulate and
approve a business plan for the following twelve-month period and shall review
the operations of MSD for the preceding twelve months and make such changes in
the Research Program and the methods and plans of operation of MSD as the Board
of Managers deems advisable.

                                      7.


     3.4   FISCAL YEAR.  The fiscal year of MSD shall be the calendar year.

     3.5   FACILITIES.  During the term (including any extension of the term) of
this Agreement (and for such additional period thereafter as is reasonably
required to permit MSD to locate and move into alternative facilities without
disrupting MSD's operations), IGEN shall provide MSD with office and laboratory
facilities reasonably suitable for the conduct of the Research Program at IGEN's
facility in Gaithersburg, Maryland (or such other IGEN facility as IGEN may
occupy in place of the Gaithersburg, Maryland facility).  IGEN shall be
obligated to provide such facilities to MSD until MSD elects to move from such
facilities.  Such facilities shall also be available to any contractors of MSD
for the conduct of the Research Program.

     3.6   RESEARCH PERSONNEL.  At the request of MSD, IGEN shall make available
to MSD (or, at MSD's instruction, a subcontractor of MSD) IGEN personnel
reasonably necessary to permit MSD to conduct the Research Program (the "IGEN
Research Personnel").  The IGEN Research Personnel shall keep track of their
time spent working on the Research Program.  The time of the IGEN Research
Personnel spent working on the Research Program shall, at the option of the
Board of Managers of MSD, be credited against either the Initial IGEN Capital
Contribution, or credited as Class C capital contributions to MSD.  In either
case, the cost of the time of the IGEN Research Personnel shall be credited in
an amount equal to IGEN's direct cost for such time (including all amounts in
respect of salary and group insurance premiums, but not including any amount for
stock options, bonus payments, or other amounts for overhead or other indirect
costs). The IGEN Research Personnel shall, unless otherwise agreed by MSD and
IGEN, devote themselves full-time to the conduct of the Research Program. The
expense of consumable laboratory supplies used in the conduct of the Research
Program shall be credited as Class C capital contributions to MSD. The cost of
such supplies shall be credited in an amount equal to IGEN's direct cost of such
supplies (not including any overhead or other indirect costs). IGEN hereby
assigns to MSD all information inventions, improvements, compositions of matter,
processes, material, data, drawings, and know-how, whether or not patented or
patentable, developed by employees, consultants, contractors, or other personnel
of IGEN, including, without limitation, the IGEN Research Personnel, related to
the subject matter of the Research Program, or related to the Research
Technologies (each a "Development") including, without limitation, Developments
made prior to the date hereof. IGEN shall ensure that all such IGEN employees,
consultants, contractors and other personnel, and the IGEN Research Personnel
execute an agreement reasonably satisfactory to MSD in which each such person
agrees to:

          (a) protect and maintain trade secrets or other Confidential
Information (as defined in Section 5.1 hereof) received pursuant to, or arising
out of, the Research Program;

          (b) report promptly to MSD (or a subcontractor of MSD) each
Development and all other discoveries, inventions or improvements of whatever
nature conceived 

                                      8.

 
solely or jointly by him/her related to, or as a result of, or
derived from the Research Program;

          (c) execute any and all papers or other documents necessary for the
protection of any Development, including a written assignment thereof to MSD (or
a subcontractor), as appropriate under this Section 3.6; and

          (d) cooperate with MSD (or a subcontractor) in the filing and
prosecution of any patent applications.

IGEN assumes the risk of, and all responsibility for, the acts or omissions of
its employees, consultants and other personnel in connection with the conduct of
the Research Program and for the activities related to the Research Program
carried on at IGEN's facilities, and shall defend, indemnify and hold MSD (and
any subcontractor of MSD) harmless from and against any and all claims made
against MSD (or any subcontractor of MSD) by IGEN personnel or third parties
arising out of the conduct of the Research Program. IGEN will maintain in force
adequate insurance to cover risk of liability resulting from the conduct of the
Research Program.

     3.7   OTHER SERVICES AND SUPPORT.  At the request of MSD, IGEN shall, to
the extent practicable given IGEN's resources, provide MSD with such
administrative and operating services as MSD shall reasonably require. IGEN
shall supply such services at IGEN's direct cost for such services (including
all amounts in respect of salary and group insurance premiums, but not including
any amount for stock options, bonus payments, or other amounts for overhead or
other indirect costs). Such services shall include, without limitation,
accounting, financial management, human resources, legal, secretarial,
regulatory compliance and maintenance services, and other similar services.
IGEN's funding of such services shall be Class C capital contributions to MSD
made in accordance with Section 2.4.2 of this Agreement.

     In addition, whenever MSD requires other services, facilities or materials,
the Board of Managers shall determine whether such can be obtained from IGEN.
If IGEN, to the extent practicable given its resources, has the ability to
supply the needed services, facilities or materials, it shall do so at its
direct cost for such services (including all amounts in respect of salary and
group insurance premiums, but not including any amount for stock options, bonus
payments, or other amounts for overhead or other indirect costs).  The value of
any services and materials (but not facilities) that IGEN provides shall be
treated as Class C capital contributions to MSD.  Subject to the terms of the
MST/MSD License, any such services contract shall provide that all results of
such work, including all intellectual property rights, are owned by MSD, and
shall be subject to approval by the Board of Managers.

     3.8   DISTRIBUTION.  It is anticipated by the Members that MSD will be able
to utilize the distribution network of IGEN.  If MSD wishes to do so, IGEN will
agree to distribute any 
                                      9.


MSD product for a fee equal to [   *   ] of distributing such product.
Unless otherwise agreed in writing by MSD and IGEN, MSD shall retain ownership
of any data or other information derived from the use of the MSD's products,
processes or services. IGEN shall, however, be permitted to manufacture, market
and sell, for research purposes only, a magnetic bead based 96 well micro-titer
reader.

     3.9   PUBLICATION CONTROL.  Because of issues related to the prosecution of
the patent applications set forth on Exhibit A to the MST/MSD License, and to
Jacob Wohlstadter's ("Wohlstadter") doctoral research, all publications that are
based in whole or part on such patent application, the inventions disclosed
therein, or the Research Program must be approved by Wohlstadter prior to
submission for publication and shall list Wohlstadter as last author or, at
Wohlstadter's election, first author when written by Wohlstadter.  Any reduction
to practice of inventions described in or arising from such patent application
shall be under the direction and guidance of Wohlstadter.

     3.10   INTELLECTUAL EXCHANGE.  Subject to the provisions of Section 5
hereof, all research and development activities, including all invention
disclosures and patent applications, shall be disclosed to the Board of Managers
as soon as practical, and MST and representatives of IGEN shall have the right
to participate in scientific discussions with MSD research staff.

     3.11   EMPLOYMENT OF WOHLSTADTER.  IGEN will repay to Wohlstadter his
reasonable travel expenses, living expenses and other out-of-pocket expenses
involved in providing technical assistance and guidance to the Research Program,
and legal expenses in establishing and maintaining this Agreement and the
relationship.  All such expenses paid by IGEN, with the exception of legal and
other expenses incurred prior to the date hereof, or incurred in establishing
this Agreement, shall be Class C capital contributions to MSD made in accordance
with Section 2.4.2 of this Agreement.  In addition, upon the termination of
Wohlstadter's Howard Hughes fellowship (or other graduate school support), MSD
and Wohlstadter will enter into a written employment agreement (the "Employment
Agreement") reasonably satisfactory to the Members and Wohlstadter setting forth
the scope of Wohlstadter's responsibilities (including a provision concerning
restrictions on Wohlstadter as specified in Section 4.1 hereof) providing that
Wohlstadter's employment will commence June 1, 1996, at which time Wohlstadter
will receive a bonus of $60,000, and providing for the payment of an annual
salary at the rate set forth below:
 

     Commencement (June 1, 1996) - September 30, 1996      $ 75,000
     October 1, 1996 - September 30, 1997                  $ 85,000
     October 1, 1997 - September 30, 1998                  $ 95,000
     October 1, 1998 - September 30, 1999                  $105,000
     Thereafter                                            $115,000

The foregoing amounts may be adjusted by written agreement of MSD and
Wohlstadter.  Salary after the fifth year following the date hereof shall be as
mutually agreed between MSD 

                                      10.
                                                       [*Confidential Treatment]

 
and Wohlstadter, subject to a written employment agreement reasonably
satisfactory to the Members and Wohlstadter setting forth the scope of
Wohlstadter's responsibilities (including a provision concerning restrictions on
Wohlstadter as specified in Section 4.1 hereof). The foregoing salary amounts
shall be adjusted for inflation each year.

4.   FUTURE DEVELOPMENTS: COMPETITION: LICENSES.

     4.1   [   *   ] Except as provided below, and except for MSD's
right to contract with third parties for the performance of one or more of its
obligations, MST and IGEN agree that MSD shall be their and Wohlstadter's
[   *   ] of conducting [   *   ] and making, using and selling [   *   ] and 
neither MST, IGEN, nor Wohlstadter shall [   *   ] with respect to such 
[   *   ] The Employment Agreement shall contain a provision whose effect shall 
be to restrict Wohlstadter as specified in the foregoing sentence.  In addition,
IGEN agrees that during the term of this Agreement, IGEN will not directly or 
indirectly develop, manufacture, market or sell, or allow IGEN's technology to 
be used to develop, manufacture, market or sell products, processes or services
utilizing, or related to, the Research Technologies.  MSD and IGEN shall work 
together, so far as is practicable, to manage the marketing of their respective 
products and processes in a complementary manner.  Each of IGEN and MSD shall, 
prior to filing, disclose to the other the subject matter of patent 
applications or continuations in part filed after the date hereof that cover 
diagnostics for human, clinical, research, environmental, agricultural, 
veterinary, food testing, industrial or similar purposes.  All such information 
shall be deemed to be "Confidential Information" (as such term is defined in 
Section 5.1 hereof) for purposes of this Agreement.  Any Member and any 
Affiliate of any Member may engage in or possess any interest in other business
ventures of any kind, nature or description, independently or with others,
unless such ventures are in competition with MSD with respect to such products
or processes. No party to this Agreement by virtue of this Agreement shall have
any rights or obligations to such independent ventures or the income or profits
or losses derived therefrom and the pursuit of such ventures shall not be deemed
wrongful or improper. No Member or any Affiliate or any Member shall be
obligated to present any particular business opportunity to MSD unless such
opportunity is directly related to the business of MSD.

     4.2   IGEN DEVELOPMENTS.  Promptly following the execution of this
Agreement, IGEN and MSD shall execute the IGEN/MSD License Agreement which
agreement shall be in the form of Exhibit E.

     4.3   MSD DEVELOPMENTS.  Subject to the terms of this Agreement and the
MST/MSD License, MSD shall be the sole and exclusive owner of all inventions,
concepts, know-how and technology developed by it, and of all patent
applications, patents and copyrights thereon.


                                      11.
                                                      [* Confidential Treatment]


          4.3.1   LICENSE TO IGEN OF ECL IMPROVEMENTS.  In the event that,
during the course of performing the Research Program, MSD develops ECL
Improvements, or MSD Improvements, MSD hereby grants to IGEN an exclusive,
worldwide, royalty-free license to such improvement for use in the Diagnostic
Field, provided, however, that IGEN may not make, use or sell products,
processes or services utilizing such improvements if doing so would violate the
provisions of Section 4.1.

          4.3.2  ROYALTIES.  In the event IGEN ceases to be a Class A Member of
MSD, then IGEN shall pay to MST a royalty of 3% of Net Sales of MSD Products.
Such amounts shall be paid to MST within 60 days of the end of the quarter in
which the sale giving rise to such royalty occurred.  Royalty payments shall be
made after deducting any withholding amounts required to be paid in connection
with the payment of such royalty.  The royalty obligation set forth above shall
terminate on a country-by-country, product-by-product basis upon the expiration
of the last to expire of the patents in a given country that would be infringed
by the sale of such MSD Product in such country absent a license to such patent
from MST.  IGEN shall be under no obligation to sell any MSD Products.

     4.4   RIGHT OF NEGOTIATION.  In the event that MST desires to grant a
license with respect to the Licensed Technology for a use outside the Diagnostic
Field, the Board of Managers of MSD, with the MST Manager abstaining from
voting, shall have thirty (30) days in which to notify MST that MSD wishes to
negotiate for such license.  If within such period MSD provides notice that it
does wish to negotiate for such license, the parties shall promptly commence
exclusive negotiations in good faith.  If the parties are unable to conclude
such a license within ninety (90) days, or if MSD has notified MST that it no
longer wishes such a license, or if MSD has failed to respond within the initial
thirty (30) day period, MST shall be free to negotiate and conclude a license
for such field with any other person.

5.   CONFIDENTIALITY.

     5.1   CONFIDENTIAL INFORMATION.  "Confidential Information" shall mean any
and all information disclosed by any party hereto to another in accordance with
the terms hereof or pursuant to the MST/MSD License Agreement, the IGEN/MSD
License Agreement, or the MSD/MST Sublicense Agreement of even date herewith
among the parties hereto, including any and all patent applications and any and
all information concerning the distribution network of IGEN (specified in
Section 3.8 hereto). Confidential Information may include information disclosed
in writing, orally or through inspection of facilities or products of a party.
Confidential Information disclosed in written or photographic form or on
magnetic or other media shall be clearly and conspicuously marked as
"confidential" or "proprietary" information. Any proprietary disclosure, if made
orally, shall be promptly confirmed in writing by the disclosing party and
identified as proprietary information by the disclosing party, if the disclosing
party wishes to keep such information confidential.


                                      12.


     5.2   TERM OF CONFIDENTIALITY.  During the term of this Agreement and
thereafter, for ten (10) years after the termination or expiration of this
Agreement, each of the parties shall hold confidential the Confidential
Information of the other parties and shall not disclose it to any third party,
without prior written consent of the party owning such Confidential Information.
Where Confidential Information of IGEN, MST or MSD is disclosed between the
parties, the receiving party may not disclose such Confidential Information to
any other party, without the consent of the disclosing party, except as
necessary for the performance of this Agreement.

     5.3   USE OF CONFIDENTIAL INFORMATION.  Each party may use the Confidential
Information of another party disclosed to it only for the purposes authorized by
this Agreement or the MST/MSD License; provided, however, subject to Board of
Managers' approval, that limited disclosure may be made for sales, assignments
or transfers under Section 6.1 hereof.  No party may use the Confidential
Information of another party in any patent application or similar document,
without the express written consent of the disclosing party.  The obligation of
confidentiality shall survive for ten (10) years following termination of this
Agreement.

     5.4   EXCEPTIONS.  The foregoing restrictions in Sections 5.1, 5.2 and 5.3
hereof shall not apply to:

          (a) information which, at the time of disclosure, is in the public
domain;

          (b) information which, after disclosure, becomes part of the public
domain by publication or otherwise, other than by a breach of this Agreement;

          (c) information which a party receiving such information from another
party (the "Receiving Party") can establish by written documentation was in its
possession at the time of disclosure by the transmitting party (the "Disclosing
Party");

          (d) information which the Receiving Party can establish it received
from a third party who has the right to disclose it; and

          (e) information which the Receiving Party is obligated to disclose by
law or in legal proceedings; provided, however, that the Receiving Party shall
provide prompt notice of any need to make such disclosure and cooperate with the
Disclosing Party in obtaining available protective orders, if any, relating
thereto.
 
     5.5   MST PUBLICATION RIGHTS.  MST (or Wohlstadter) may publish results of
research performed under this Agreement and otherwise relating to the Research
Program.  MST shall first give MSD and IGEN notice of its or Wohlstadter's
intention to publish such results, and a reasonable period (not to exceed 60
days) to prepare and file a patent application thereon.


6.   RIGHTS AND OBLIGATIONS REGARDING MSD MEMBERSHIP INTERESTS.


                                      13.

 
     6.1   RESTRICTION ON RESALE.  Unless otherwise unanimously agreed to in
writing by the Members, or as otherwise required by this Agreement, no party to
this Agreement may resell, assign, transfer, mortgage or otherwise encumber any
interest as a member of MSD or other interest in MSD held by such Member.

7.   DISPUTE RESOLUTION.

     7.1   BUSINESS DECISIONS AND DISAGREEMENTS.  In the event that the Board of
Managers are unable to agree upon or resolve a dispute concerning the Research
Program or the operating plan (specified in Section 3.3 hereof), the Board of
Managers shall consult with the Scientific Advisory Board of MSD, or other
advisors familiar with the technical aspects of the Research Program in order to
resolve such dispute.

     7.2   DISPUTES CONCERNING CONTRACTUAL OBLIGATIONS.  Upon execution of this
Agreement, each party hereby designates the person listed opposite its name to
act as its representative who shall have the initial responsibility for
discharging or causing to be discharged the responsibility of that party for the
performance of this Agreement:

          Party      Representative
          -----      --------------

          MSD:      Chief Executive Officer
          IGEN:     Richard J. Massey
          MST:      Jacob Wohlstadter

     In the event that any dispute arising out of, or related to this Agreement
(except for any dispute concerning the Research Program or operating plan
resolved pursuant to Section 7.1 hereof), or the breach, termination or validity
hereof, cannot be resolved by the representatives of the parties, such dispute
may be referred by either party for resolution by final and binding arbitration
conducted in Washington, D.C., by an arbitrator mutually agreeable to each of
the Members or, in the event the parties cannot agree on a single arbitrator, by
three arbitrators, selected as stated below, under the patent arbitration rules
of the American Arbitration Association then in effect.  Arbitration of any such
issue may be commenced by written notice from one party to the other designating
the arbitrator selected by the party giving such notice.  The party receiving
such written notice shall within sixty (60) days designate a second arbitrator
and the two arbitrators together shall mutually select a neutral third
arbitrator. Each arbitration shall be conducted at a site selected by the three
arbitrators. The arbitrators shall have no power to add to, subtract from or
modify any of the terms or conditions of this Agreement. The arbitrators shall
render their decision in writing within sixty (60) days of the hearing and shall
provide the bases on which they reached their decision. Any award rendered in
such arbitration may be enforced by either party in any court or forum (state or
federal) having jurisdiction, to whose jurisdiction for such purposes each
Stockholder hereby irrevocably consents and submits.

                                      14.

 
8.   TERM AND TERMINATION.

     8.1   TERM.  Except as otherwise agreed by the Members, and unless a
product has been developed by such date, the term of this Agreement shall expire
on the earlier of the fifth anniversary of the date of this Agreement, or such
time as MSD shall be unable to continue operations as a result of a lack of
funds.

     8.2   EXTENSION OF TERM.  If no product has been developed by the time this
Agreement is set to expire as determined pursuant to Section 8.1 above, MSD
shall prepare and submit to IGEN a written research plan and budget (the
"Additional Research Budget") for the conduct of additional research.  IGEN
shall, within 90 days of IGEN's receipt of the Additional Research Budget,
determine whether to extend the term of this Agreement and provide the funding
specified in the Additional Research Budget.  If IGEN elects to provide such
funding, such funding shall be in the form of a Class C capital contribution in
MSD.  In the event IGEN elects not to fund such additional research, IGEN, MST
and MSD shall work in good faith and shall use reasonable efforts to secure
third-party funding of the Additional Research Budget.  In the event a
definitive agreement has not been executed within 180 days of IGEN's receipt of
the Additional Research Budget providing for funding as set forth in the
Additional Research Budget, this Agreement shall expire, and MST and MSD shall
have the rights set forth in Section 8.5.3.  MST agrees not to block any such
extension of the term of this Agreement as a member of the Board of Managers.
If no product has been developed during any such extended term, this Agreement
shall terminate upon the expiration of such extended term.

     8.3   TERMINATION BY AGREEMENT.  This Agreement may be terminated at any
time by the unanimous written agreement of the Members.

     8.4   TERMINATION FOR BREACH.  MST may terminate this Agreement if IGEN
shall have defaulted on its obligations to fund the Research Program pursuant to
Section 2.4 hereof or if IGEN shall have materially defaulted on its obligations
pursuant to Section 3.5 or 3.6 hereof, and any default under this Section 8.4
shall continue for thirty (30) days following written notice thereof to two
officers of IGEN from MST.

     8.5   CONSEQUENCES OF TERMINATION.

          8.5.1  In the event that this Agreement is terminated pursuant to
Section 8.3, the parties shall agree on the consequences of such termination.
 
          8.5.2  In the event that MST terminates this Agreement pursuant to
Section 8.4, MST shall have the right to purchase all of IGEN's interest as a
Class A member of MSD at a price of $10,000, and to purchase all of IGEN's
interest as a Class B and Class C Member of MSD at a price of $1.00.  In such
event, IGEN hereby consents to such sale as a Member of MSD.  Upon termination
of this Agreement by MST 

                                      15.

 
pursuant to Section 8.4, the MST/MSD License shall terminate immediately and the
license granted to MSD therein shall also immediately terminate.

          8.5.3 In the event that this Agreement expires as provided in Section
8.1, and it is not extended as provided in Section 8.2, or in the event that
this Agreement is extended, but upon the expiration of the extended term, is not
further extended, or if MST elects pursuant to Section 2.5 to terminate this
Agreement, then MSD and MST shall jointly have the right to purchase all of
IGEN's interest as a Class A Member, Class B Member and Class C Member of MSD by
paying to IGEN an amount equal to (1) the difference, if any, between (i) the
amount of the Initial IGEN Capital Contribution previously paid to MSD, and (ii)
the aggregate amount of Net Profits (as defined in the LLC Agreement)
distributed to IGEN as of such expiration or termination of this Agreement and
(2) the sum of (i) the Adjusted Cumulative Class C Capital Contributions (as
such term is defined in the LLC Agreement) plus (ii) the Preferred Return
Amounts (as such term is defined in the LLC Agreement) still outstanding.  Such
amount shall be paid to IGEN not later than the date such amount would have been
paid to IGEN under the terms of the LLC Agreement.  Upon payment of such amount,
IGEN shall cease to be a Class A, Class B and Class C Member of MSD.  In such
event, IGEN hereby consents to such sale as a Member of MSD.

          8.5.4 In the event that MST does not exercise its rights under Section
8.5.2, or MSD and MST do not exercise their rights under Section 8.5.3, then MSD
shall be liquidated and any proceeds remaining following payment or provision
for liabilities shall be distributed to the Members of MSD in accordance with
the LLC Agreement and the Certificate, as then in effect.

          8.5.5 In the event that MST exercises its rights under Section 8.5.2
or MSD or MST exercises its rights under Section 8.5.3, IGEN hereby agrees to
(i) remove from the Board of Managers its designee and elect a second designee
of MST, (ii) vote all of its Voting Interest in the manner requested by MST,
provided that in the case of the exercise by MSD or MST of its rights under
Section 8.5.3, IGEN shall not be obligated to vote in favor of any amendment to
the LLC Agreement that would diminish IGEN's priority position with respect to
the payment to IGEN of Net Profits of MSD, and (iii) otherwise provide
reasonable cooperation and provide such consents (including the execution of
such amendments to this Agreement and other documents as may be reasonably
required) to permit MSD to raise additional capital.

9.   REPRESENTATIONS.

     9.1   AUTHORIZATION.  Each of IGEN and MST represents to the other parties
that it has the power and authority to enter into this Agreement (including all
Exhibits) and to perform its obligations hereunder, and that the execution,
delivery and performance hereof has been duly and validly authorized.


                                      16.


     9.2   NO BREACH.  Each party hereby severally represents to all other
parties that its entry into and performance under this Agreement (including all
Exhibits) will not constitute a breach of any agreement or duty to or by which
such party is bound, and will not violate any law or governmental regulation
applicable to such party.


10.  MISCELLANEOUS PROVISIONS.

     10.1   This Agreement may not be assigned by any party without the prior
written consent of the Members.  The rights of any party hereunder shall not
extend to any party purchasing or otherwise acquiring any Voting Interest, or
other economic interests in MSD from such party, unless and to the extent agreed
to by the Members.

     10.2   If any provision or provisions of this Agreement shall be held
invalid, illegal or unenforceable, the validity, legality or enforceability of
the remaining provision(s) shall not be affected.

     10.3   As this Agreement relates to the governance and internal affairs of
a Delaware limited liability company and relations among its members, this
Agreement shall be governed by and interpreted, construed and enforced in
accordance with the laws of the State of Delaware without regard to the
principles of conflicts of laws.

     10.4   No delay or failure by any party in exercising any rights hereunder
shall be deemed to constitute a waiver of such rights or any other rights
hereunder.

     10.5   All notices, requests, consents, demands or communications called
for under this Agreement shall be in writing and shall be personally delivered,
mailed, postage prepaid, telecopied or telegraphed as follows:

          (a)  If to MSD to:

                    MESO SCALE DIAGNOSTICS, LLC.
                    16020 Industrial Drive
                    Gaithersburg, MD 20877
                    Attn: President
                    Facsimile: (301) 208-3799


                                      17.


          (b)  If to IGEN:

                    IGEN, Inc.
                    16020 Industrial Drive
                    Gaithersburg, MD 20877
                    Attn: Richard J. Massey, Ph.D.
                    Facsimile: (301) 230-0158

 
               with a copy to:

                    Wilmer, Cutler & Pickering
                    2445 M Street, N.W.
                    Washington, D.C. 20037
                    Attn: Stephen P. Doyle, Esq.
                    Facsimile: (202) 663-6363


          (c)  If to MST to:

                    MESO SCALE TECHNOLOGIES, LLC.
                    9919 Gable Ridge Terrace, Apt. G
                    Rockville, MD 20850
                    Attn: Jacob Wohlstadter
                    Facsimile: (617) 354-1912

               with a copy to:

                    Ropes & Gray
                    One International Place
                    Boston, MA 02110
                    Attn: Gregory E. Moore
                    Facsimile: (617) 951-7050

or such other address as may be furnished in writing to the parties hereto.  All
such notices, requests, demands and other communications shall, when mailed
(registered or certified mail, return receipt requested, postage prepaid),
personally delivered, or telegraphed, be effective four days after deposit in
the mails, when personally delivered, or when delivered to the telegraph
company, respectively addressed as aforesaid, unless otherwise provided herein
and, when telecopied, shall be effective upon actual receipt in legible form by
the recipient at such address and when the recipient has been requested to
acknowledge receipt of the entire telecopier transmission upon the sending or
receiving of the acknowledgment of receipt (which acknowledgment the recipient
will promptly give.)

                                      18.

 
     10.6   This Agreement may not be modified or amended, altered or changed
except by written agreement signed by the parties against whom such change is
asserted.

     10.7   The provisions of Sections 4.2, 4.3, 5, 6, 7, 8, 9, and 10 shall
survive termination of this Agreement for any reason.

     10.8   This Agreement includes the following Exhibits, each of which
constitutes an integral component part of this Agreement and which must be
attached before this Agreement shall become effective:

          Exhibit A Research Outline
          Exhibit B MSD Limited Liability Company Agreement
          Exhibit C MSD Certificate of Formation
          Exhibit D MST/MSD License Agreement
          Exhibit E IGEN/MSD License Agreement

     10.9  This Agreement, including all Exhibits hereto, constitutes the entire
agreement among the parties with respect to the financing and operation of MSD
and supersedes all prior written or oral communications and agreements with
respect to the financing and operation of MSD among the parties and any employee
or agent thereof, all of which are hereby terminated.

     10.10  This Agreement may be executed in one or more counterparts, each of
which shall be an original but all of which shall together constitute a single
agreement.

     10.11  Each party hereto agrees not to disclose the terms and conditions of
this Agreement or documents issued hereunder, except as may be required by law
or government rule or regulation, and except to third parties as may be required
for financing purposes (such third parties being required to hold such facts and
terms and conditions in confidence), without the express written consent of the
Members .

     10.12  This joint venture and this Agreement entered into by the parties
does not constitute a partnership under Title 6, Chapter 15 of the Delaware Code
or a limited partnership under Title 6, Chapter 17 of the Delaware Code (but
does constitute a limited liability company under Title 6, chapter 18 of the
Delaware Code) and no party has the power or authority to bind any other party
or to incur any liabilities on any other party's behalf.

                  [Remainder of Page Intentionally Left Blank]
 

                                      19.

 
     IN WITNESS WHEREOF, the parties have caused this Agreement to be executed
by their duly authorized representatives as of the date first written above.

MESO SCALE DIAGNOSTICS, LLC.              IGEN, INC.



By:    /s/ Jacob Wohlstadter              By:     /s/ Richard Massey
   ------------------------------            ------------------------------
Name:     Jacob Wohlstadter                  Name:      Richard Massey
Title:    President                          Title:     President



                                          MESO SCALE TECHNOLOGIES, LLC.



                                          By: /s/ Jacob Wohlstadter
                                             ------------------------------ 
                                             Name:     Jacob Wohlstadter
                                             Title:    President
 


                                      20.

 
                                LIST OF EXHIBITS


Exhibit A:   Research Outline

Exhibit B:   Limited Liability Company Agreement

Exhibit C:   Certificate of Formation

Exhibit D:   MST/MSD License

Exhibit E:   IGEN/MSD License Agreement
 
                                      21.


 
                                   EXHIBIT A

                                RESEARCH OUTLINE


     The research will be conducted under the direction and guidance of
Wohlstadter. The Research initially shall be directed at the use in diagnostic
procedures, including diagnostic procedures utilizing electrochemiluminescent
("ECL") technology, of (i) the [ * ] disclosed in United States Patent 
Application Serial No. [ * ] and (ii) [ * ] and [ * ] the [ * ] and/or [ * ]
(e.g., through [ * ] and [ * ] and [ * ] (e.g., through [ * ] and [ * ] and
(iii) [ * ] (e.g., [ * ] The foregoing specifically includes, but is not
limited to, [ * ] (e.g., [ * ] and/or [ * ] and [ * ] and/or [ * ] as well as
the use of [ * ] and/or [ * ] of an [ * ] in the [ * ] (e.g., [ * ]

                                      22.
                                                       [*Confidential Treatment]