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                                                                    Exhibit 10.7


                               BIO NEBRASKA, INC.


                              EMPLOYMENT AGREEMENT

         This Employment Agreement, dated as of September 18, 1989, between Bio
Nebraska, Inc., a corporation incorporated and existing under the laws of
Nebraska and having its office in Lincoln, Nebraska (hereinafter referred to
along with its subsidiaries and affiliates as the "Company" unless the context
otherwise requires), and Mal Riddell, residing at 29 Robin Road, Moorestown,
N.J. 08057 (hereinafter referred to as the "Executive").

         WHEREAS, the Company desires to employ the Executive to manage the
start-up of certain new businesses, generally as described in a Memorandum,
dated August 24, 1989, from Tom Coolidge to the Executive, a copy of which is
attached hereto as Appendix A (being referred to herein as the "Memorandum") and
the Executive desires to be so employed.

         NOW THEREFORE in consideration of the foregoing and of the mutual
promises hereinafter set forth, the parties hereto agree as follows:

1.       EMPLOYMENT AND TITLE, POWERS, DUTIES, FUNCTIONS AND OBJECTIVES.

         The Company shall employ the Executive and the Executive shall perform
services for the Company and any of its subsidiaries or affiliates with such
authority and with such powers and duties as may be described or assigned to him
by the Board of Directors of the Company and by the Chairman of the Board.

         The Executive's title shall be Managing Director. He shall also be made
President of any subsidiaries or divisions of the Company which may be
established, and which the Executive shall be assigned to manage, for the
purpose of commercializing elements of the Company's technologies. The Executive
shall also be invited to attend and participate in meetings of the Board of
Directors of the Company and of the Company's Advisory Board with respect to
which the Executive shall be an EX OFFICIO member.

     Generally, the Executive's functions and objectives in his employment with
the Company are expected to be as described in paragraphs 2, 3 and 5 of the
Memorandum, but these may be modified as the Company's business develops.

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2.   REPORTING AND SUPERVISION.

         In carrying out his functions, the Executive shall report to the
Chairman of the Board of the Company on all matters, but will work closely with
the President of the Company on all scientific development. He will be
ultimately responsible to the Board of Directors and the shareholders of the
Company.

3.       EXCLUSIVITY.

         The Executive agrees that during the term of his employment hereunder
he will devote his entire business time, energy, skill and resources to his
duties hereunder and to the affairs and interests of the Company and its
subsidiaries and affiliates; and he will not, without the prior written consent
of the Board of Directors of the Company, directly or indirectly (a) engage in
any compensated activity for any person other than the Company or any affiliate
or (b) engage in any business or professional activity other than on behalf of
the Company, whether or not such activity is pursued for financial gain.

4.       COMPENSATION.

         During the Executive's employment with the Company, the Company shall
pay to the Executive a base salary at the rate of one hundred thousand (100,000)
dollars per year, to be paid in equal monthly installments at the end of each
month.

5.       ADDITIONAL BENEFITS.

         (A) The Executive shall be provided with health, hospitalization and
accident insurance benefits as generally provided under the Company's and its
affiliates' group policies.

         (B) The Executive shall be provided with savings and retirement plan
benefits as generally provided under the Company's and its affiliates' plans.

6.       VACATION.

         The Executive shall be entitled to six weeks of vacation for each full
year of his employment hereunder, with the understanding that he will use his
best efforts to see that any vacation taken by him will not adversely impact the
businesses he is managing for the Company.

7.       BONUS COMPENSATION.

         In the event the objectives which the Company and the Executive will
set out for the near term progress of the business to be managed by the
Executive (referred to herein as the "Objectives") are accomplished by him as
determined by the Board of Directors, he will be entitled to receive bonus
compensation relative to the net cash flow of the new OPE and PP Businesses in
accordance with paragraph 10 of the Memorandum which is incorporated herein by
reference. He may also


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become entitled to additional bonus compensation based on the net cash flow
of other new businesses as contemplated in such paragraph 10.

8.       EQUITY INCENTIVES.

         Assuming the Objectives are accomplished by the Executive as determined
by the Board of Directors, he will be entitled, on a progressively vesting
basis, to both (i) a Designated Interest in the net book/market value of the OPE
Business and of the SM Business (as those terms are used in the Memorandum) and
(ii) stock appreciation rights (referred to as "SAR's) in the Company, all as
set forth in paragraph 11 of the Memorandum which is incorporated herein by
reference. In the event that there is a material change in the federal income
tax laws relative to the treatment of long term capital gains so that the form
of incentive provided by an SAR is substantially disadvantaged from a tax
standpoint compared with the ownership of shares of stock, then the parties
shall revisit the SAR form of incentive with a view towards providing an
incentive to the Executive which will have some or all of the advantages for
long term capital gains available under any such new tax laws.

9.       SUPPORT FACILITIES AND EXPENSES.

         The Company shall provide support facilities to the Executive,
generally as described in paragraph 6 of the Memorandum.

         The Company shall reimburse to the Executive all reasonable travelling,
hotel, entertainment and other out-of-pocket expenses which he may from time to
time be authorized to incur in the execution of his duties hereunder.

10.      NON COMPETITION.

         The Executive agrees that during the term of his employment hereunder
and for a one-year period thereafter the Executive shall not directly or
indirectly do any of the following:

                  (i) Engage in, be employed by or affiliated with, finance or
         assist others to operate, establish or acquire any business activity
         that is competitive with the business which is being conducted by the
         Company or by any of its affiliates or subsidiaries or with any
         business for which substantial planning is made by the Company or by
         any of its affiliates or subsidiaries;

                  (ii) Divert, disrupt or otherwise interfere in any way with
         any business relationship of the Company or any of its affiliates or
         subsidiaries with any of their respective clients, customers or
         business contacts;

                  (iii) Solicit for employment for his own or another's benefit
         (as employee, partner, independent contractor or otherwise) any person
         who has been employed by the Company or any affiliate within the two
         year period prior to the date in question.


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         During any such one year period after termination of this Agreement
during which the Executive is required to adhere to the foregoing
restrictions, and during which the Executive has no bonus, DI or SAR rights
which could result in payments to him during or after such period, the
Executive shall be paid a fee at the end of such year period, assuming full
compliance with this Paragraph 8, equal to 25% of the basic salary which he
received during the last full year of employment with the Company.

11.      CONFIDENTIALITY AND OTHER REQUIREMENTS.

         (A) As between the Company or any of its subsidiaries or affiliates, as
the case may be, and the Executive, all products, methods, processes,
discoveries, materials, ideas, creations, inventions, plans, strategies and
other intellectual properties pertaining to the business of the Company or any
of its subsidiaries or affiliates, developed or invented by the Executive or by
others affiliated with the Company, whether or not developed or discovered
during regular working hours, shall be the sole and absolute property of the
Company or its respective subsidiary or affiliate, for any and all purposes. The
Executive shall not claim to have, under this Agreement or otherwise, any right,
title or interest of any kind or nature in any of the foregoing.

         (B) The Executive acknowledges that in the course of his employment
hereunder he will make use of, acquire and add to proprietary information of the
Company and its subsidiaries and affiliates which shall be of a special and
unique nature and value relating to such matters as plans, strategies, trade
secrets, technical systems and procedures, inventions, manuals, confidential
reports, customer business and similar matters. The Executive agrees that with
respect to any of the foregoing, during and following the term hereof, for so
long as the same remains confidential (and beyond should loss of confidentiality
be caused by the Executive), he will not, for any purpose, divulge or disclose
any of such proprietary information to others or let others use such information
for any purpose other than for the benefit of the Company or its subsidiaries or
affiliates, as the case may be. The Executive shall promptly, whenever requested
by the Company and in any event upon the termination of his employment with the
Company hereunder, deliver to the Company all reports, laboratory notes,
correspondence and all other documents, papers and records which may have been
prepared by him or have come into his possession in the course of his employment
hereunder; and, after termination of this agreement, the Executive shall not be
entitled to and shall not retain any copies thereof unless otherwise agreed to
in writing by the Company.

         (C) In the event any of the Executive's activities or services give
rise to the creation of an idea or invention which by itself, or in combination
with the efforts of others, may be, in the judgement of the Company,
appropriately the subject of an application for patent, copyright, trademark or
tradename or similar intellectual property right, the Executive shall, at the
Company's request and expense, prepare and execute all such documents (including
assignments of all of his interests therein to the Company) and take all such
other action as may in the opinion of the Company or its advisors be necessary
or advisable to secure property and other rights therein for the Company and to
obtain the issuance of any such patent, copyright, trademark, trade name or
other right in any jurisdiction on behalf of the Company.


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12.      TERM OF EMPLOYMENT.

         This Agreement shall initially be for a term of one year, and shall
continue thereafter for successive one year terms unless terminated by either
party by giving six months' notice thereof prior to the end of any such term.

         Notwithstanding the foregoing, the Company shall be entitled, by giving
notice in writing to the Executive, to terminate forthwith this Agreement and
his employment hereunder for cause including any misconduct on the part of the
Executive or any material breach of his obligations to the Company hereunder or
otherwise.

         Any termination of this Agreement shall in no manner relieve the
Executive of his obligations under Paragraphs 10 and 11 hereof. Any termination
of this Agreement other than for cause shall not impair any vested right the
Executive may have achieved relative to bonuses and equity incentives pursuant
to Paragraphs 7 and 8 hereof.

13.  NOTICES.

         All notices hereunder shall be in writing and delivered personally or
by registered or certified mail. Such notices shall be addressed to the Company
at its principal office and to the Executive at the address stated in the first
paragraph of this Agreement, or in either case at such other address as shall be
designated in writing by the party to whom the notice is to be sent. Any such
communication so sent by mail shall be deemed given three days after mailing and
immediately upon delivery.

14.      MISCELLANEOUS.

         This Agreement constitutes the entire agreement of the parties hereto
relating to the subject matter covered hereunder and there are no written or
oral terms or representations made by either party other than those contained
herein. All of the terms and provisions of this Agreement shall be binding upon
and shall inure to the benefit of and be enforceable by and against the parties
to this Agreement and their respective heirs, executors and successors in
interest.

16.      GOVERNING LAW.

         This Agreement shall be governed and construed in accordance with the
laws of Nebraska which shall be deemed to be the primary locus of activities
hereunder. The courts, both federal and state, in that State shall have full
jurisdiction over all matters hereunder and the parties herewith submit to
service of process and to the appropriate venue of such courts with respect to
any actions brought hereunder.


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         IN WITNESS WHEREOF, the Company has caused this Agreement to be
executed by its duly authorized officer and the Executive has executed this
Agreement as of the date first written above.

BIO NEBRASKA, INC.


By: /s/ Thomas R. Coolidge                   /s/ Mal Riddell
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         Chairman of the Board               Mal Riddell, the Executive