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                                                                   Exhibit 10.51

                       PRODUCTION AND MARKETING AGREEMENT
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*** Confidential treatment has been requested as to certain portions of this
agreement. Such omitted confidential information has been filed separately with
the Securities and Exchange Commission pursuant to Rule 24b-2 under the
Securities Exchange Act of 1934, as amended, and the Commission's rules and
regulations promulgated under the Freedom of Information Act, pursuant to a
request of confidential treatment.

     This Production and Marketing Agreement (this "Agreement"), dated and
effective August 15, 2000, is between SENETEK PLC, a United Kingdom Company,
whose principal office is located at 23 Place Street, London, SW1E, 5HW England
(hereinafter referred to as "Senetek"), and SIGNET LABORATORIES, INC., a
Delaware corporation having its principal place of business at 180 Rustcraft
Road, Dedham, Massachusetts 02026 (hereinafter referred to as "Signet").

                                 WITNESSETH THAT
                                 ---------------

     WHEREAS, Senetek has a ten-year exclusive worldwide license to certain cell
lines (hereinafter the "Cell Lines"), to wit:

          1. Those certain cell lines designated "4G8" and "6E10" more
     particularly described in an Agreement by and between Research Foundation
     for Mental Hygiene, Inc. (hereinafter referred to as RFMH) and Senetek
     dated by Senetek July 21, 1994 and dated by RFMH July 12, 1994 (hereinafter
     referred to as the "Basic Agreement/ License"), as amended by Amendment #1
     dated by Senetek August 1, 1995 and dated by RFMH July 28, 1995;

          2. The monoclonal antibody designated "525 Reactive to PHF" more
     particularly described in an Agreement dated by Senetek August 1, 1995 and
     dated by RFMH July 28, 1995, said Agreement being attached as "Appendix
     A-1" to the Basic Agreement/License;

          3. Those certain cell lines designated "339 Reactive to PHF" and "3F4
     Reactive to Prion PrP (human and hamster)" more particularly described in
     an Agreement dated by Senetek August 30, 1995 and dated by RFMH May 22,
     1995, said Agreement being attached as "Appendix A-2" to the Basic
     Agreement/License;

          WHEREAS, the Basic Agreement/License provides for a ten-year exclusive
     worldwide license to cell line products (hereinafter the "Cell Line
     Products"), attached hereto as Exhibit "A" to wit: the monoclonal
     antibodies produced in any form by using the Cell Lines, including, but not
     limited to pure, Fab fragment, ascites fluid, tissue culture fluid,
     modified or conjugated (i.e., enzymes, biotin, florescent or any other
     form);

          WHEREAS, Senetek desires to grant to Signet and Signet desires to
     secure from Senetek rights to manufacture, package, promote and sell the
     Cell Line Produces--such activities to be performed in accordance with the
     terms and conditions set forth herein and subject to and in accordance with
     the terms of the Basic Agreement;

     NOW, THEREFORE, in consideration of the mutual covenants herein recited,
the parties hereby agree as follows:

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     1. Grant.
        ------

          1.1 Right to Manufacture, Package, Promote and Sell. Upon the terms
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and conditions set forth herein, Senetek hereby grants to Signet a worldwide
excusive right to manufacture, package, promote and sell the Cell Line Products.

          1.2 Acceptance by Signet. Signet hereby accepts the foregoing grant of
worldwide exclusive rights to manufacture, package, promote and sell the Cell
Line Products.

          1.3 Not a License. This grant shall not be construed as a license, by
implication or otherwise, under any applications or rights to which shall remain
with Senetek in accordance with the terms of the Basic Agreement/License.

     2. Term of Agreement. The term of this Agreement shall be contemporaneous
with the Basic Agreement/License and any and all renewals/extensions thereof,
unless terminated as hereinafter provided.

     3. Sharing of Revenues.
        --------------------

     Level 1 From the first "*Filed Separately with the Commission*" of annual
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     sales revenues received by Signet from sales of Cell Line Products, Signet
     shall retain "*Filed Separately with the Commission*" of annual sales
     revenues, plus reasonable production costs consistent with Senetek's
     agreement with Covance Research Products, Inc., plus reasonable charges for
     QA/QC compliance not to exceed "*Filed Separately with the Commission*"
     annually, plus sales and distribution taxes [including, but not limited to,
     federal manufacturer's and retailer's excise, state and local sales and use
     taxes and personal property taxes), value-added taxes, public charges,
     tariffs, import duties, quarantine charges or license fees however
     designated, levied or based on such prices (hereinafter referred to as
     "Taxes")]. The remainder of the sales revenues shall be remitted to
     Senetek. Senetek shall be responsible for all fees due to RFMH in
     accordance with the Basic Agreement/ License.

     Level 2 From annual sales revenues in excess of "*Filed Separately with the
     -------
     Commission*" received by Signet from sales of Cell Line Products, Signet
     shall pay "*Filed Separately with the Commission*"of annual sales revenues
     in excess of "*Filed Separately with the Commission*" and all fees due RFMH
     in accordance with the Basic Agreement/License. Signet is responsible for
     costs and expenses incurred in connection with the sale of Cell Line
     Products.

     Level 3 "New Cell Line Products" are described as products which are not
     -------
     listed on Exhibit A, including derivatives of Cell Line Products and
     additional products obtained from RFMH for sale under this agreement. From
     annual sales revenues received by Signet from sales of new Cell Line
     Products, Signet shall pay to Senetek "*Filed Separately with the
     Commission*" of annual sales revenues. Signet is responsible for all costs
     and expenses incurred in connection with the sale of New Cell Line
     Products. Signet shall be responsible for all fees due to RFMH in
     accordance with the Basic Agreement/License. If at any time during the

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first three (3) years of this Agreement, a derivative product significantly
impacts sales of Level 1 Cell Line Products, Senetek and Signet may re-negotiate
a revenue-sharing agreement for those derivative products.

4.       Reports.
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     4.1 Reports. Signet agrees to deliver to Senetek and RFMH within thirty
         -------
(30) days after the expiration of each calendar quarter beginning with the
calendar quarter having the first sales date following the date of this
Agreement, an accounting in writing setting forth the net proceeds of sales
during such calendar quarter.

     4.2 Records and Audits. Signet shall keep a true and exact record in
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connection with the accounting provided herein, and Senetek shall have the right
once each calendar year beginning with the first report to appoint at no cost to
Signet an independent certified public accountant to whom Signet can have no
reasonable objection, who, during the regular business hours of Signet, may
examine the accounts and records of Signet insofar as they relate to net
proceeds of sales for a period not more than two (2) years preceding the date of
inspection, for the sole purpose of verifying the correctness of any accounting
by Signet, and not for any other purpose. Said accountant shall be under an
obligation of secrecy not to disclose any information (s)he learns except (s)he
may disclose to Senetek any information which relates solely to the accuracy of
reports and payments under this Agreement.

5.       Payments.
         --------

     5.1 Payments. Payments to Senetek from Level 1 revenues and payments to
         --------
Senetek and RFMH from Level 2 and Level 3 revenues, as the case may be, shall be
due and payable thirty (30) days after the expiration of each calendar quarter.

     5.2 Currencies. All payments payable hereunder to Senetek shall be payable
         ----------
in United States Dollars (USD). If foreign exchange is freely available and
remittance of the payments provided herein is not otherwise prohibited, all
royalties due to Senetek hereunder as a result of sales in countries foreign to
the United States shall be converted (for the purpose only of calculation of
such royalties) into its equivalent in USD at the foreign exchange rate for such
foreign funds as reported in the Wall Street Journal at the close of business on
the last business day of the quarterly reporting period.

6.       Representations and Warranties.
         ------------------------------

     6.1 Signet.
         ------

          (i) Signet warrants and represents that Signet shall devote its
faithful, diligent and best efforts to distribute, market, promote and sell the
Cell Line Products, and maintain and enhance the good will of the Cell Line
Products worldwide.

          (ii) Signet warrants and represents to Senetek that it is not, and
shall not hold itself out as, the representative, agent, servant or employee of
Senetek for any purpose. This Agreement creates no relationship of joint
venture, partnership, limited partnership, or agency between the parties.

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         (iii) Signet represents and warrants that the execution of this
Agreement by Signet has been duly authorized by all necessary corporate action
of Signet and constitutes the valid and binding obligation of Signet. The
execution of this Agreement by Signet and the consummation of the transactions
contemplated hereby does not conflict with or result in a default under or
breach of: (1) Signet's Articles of Incorporation or By-laws or other
organizational documents; (2) any agreement, indenture, mortgage, contract or
instrument to which Signet is bound or by which any of its properties or assets
is subject; (3) any order, writ, injunction, decree or judgment of any court or
governmental agency applicable to Signet or to which any of its assets is bound;
or (4) any law or regulation applicable to Signet or by which any of its assets
is bound.

         (iv) Signet acknowledges that the Cell Line Products: (1) are the sole
property and confidential information of RFMH; (2) are subject to
confidentiality requirements under the Basic Agreement/License which
requirements also bind Signet; and (3) may be transferred only back to Senetek
or RFMH in accordance with the terms and requirements of the Basic
Agreement/License.

         (v) Signet agrees not to undertake any separate and independent
business relationship with RFMH in the field of neuroscience products during the
term of this Agreement.

     6.2 Senetek.
         -------

          (i) Senetek represents and warrants that it is not in default of any
term, provision or condition of the Basic Agreement/License and that its rights
thereunder are not encumbered in any manner, and the Cell Line Products are free
of any claims for infringement, patent or copyrights and trademarks of third
parties. Senetek also represents and warrants that there is no litigation, claim
or assessment pending or threatened against Senetek contesting Senetek's rights
under the Basic Agreement/License. Senetek hereby indemnifies and will hold
Signet harmless from any and all costs, expenses, claims, attorney's fees and so
forth in regard to all matters which have transpired prior to the execution of
this Agreement now known or hereafter arising from the Basic Agreement/License,
including, but not limited to, any and all claims from RFMH.

         (ii) Senetek represents and warrants that it will terminate its
Manufacturing and Distribution Agreement with Covance Research Products, Inc.
dated September 24, 1999 in accordance with the terms of said Agreement, and
that there is no litigation, claim or assessment pending or threatened against
Senetek on account thereof. Senetek will consult with Signet on the timing of
the thirty (3) day notice of termination required thereunder.

         (iii) Senetek has complied with the terms and conditions of the Basic
Agreement/License, including, but not limited to, all notice requirements and
has received all of the necessary approvals from RFMH regarding the execution of
this Agreement, including without limitation under Section 2.4 of the Basic
Agreement/License, to engage Signet to manufacture, package, promote and sell
the Cell Line Products. Copies of all such approvals in form satisfactory to
Signet will be delivered to Signet simultaneously with the execution of this

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Agreement. Senetek will deliver forthwith to Signet any and all documents
and correspondence received by Senetek from RFMH in regard to the bal. Copies of
all such approvals in form satisfactory to Signet will be delivered to Signet
simultaneously with the execution of this Agreement. Senetek will deliver
forthwith to Signet any and all documents and correspondence received by Senetek
from RFMH in regard to the Basic Agreement/License, including, but not limited
to, any and all notices of default delivered by RFMH to Senetek. Senetek hereby
grants to Signet the right to cure any and all such defaults in accordance with
the Basic Agreement/License. In the event a default is based on the failure of
Senetek to comply with the terms of the Basic Agreement/License and there is an
expenditure of time and money by Signet to cure said default, Signet shall have
the right to offset any such expenditure from future payments due from Signet to
Senetek hereunder.

         (iv) Senetek represents and warrants that the execution of this
Agreement by Senetek has been duly authorized by all necessary corporate action
of Senetek and constitutes the valid and binding obligation of Senetek. The
execution of this Agreement by Senetek and the consummation of the transactions
contemplated herby does not conflict with or result in a default under or breach
of: (1) Senetek's Articles of Incorporation or By-laws or other organizational
documents; (2) any agreement, indenture, mortgage, contract or instrument to
which Senetek is bound or by which any of its properties or assets is subject;
(3) any order, writ, injunction, decree or judgment of any court or governmental
agency applicable to Senetek or to which any of its assets is bound; or (4) any
law or regulation applicable to Senetek or by which any of its assets is bound.

7.       Termination.
         -----------

     7.1 Termination by Signet. This Agreement can be terminated by Signet at
         ---------------------
any time upon ninety (90) days written notice to Senetek, if it is determined by
Signet, in its sole and absolute discretion, that the annual sales revenues will
fall below the minimums required by Signet to make this Production and Marketing
Agreement profitable to Signet. In the event of such termination, Signet agrees
to pay to Senetek all amounts due and payable up to the effective date of such
termination. Upon such termination, Signet shall return to Senetek all
antibodies, all technical information, Cell Lines and know-how transferred to
Signet by Senetek. Signet shall have the right to sell any Cell Line Products in
inventory at the time of said termination and shall pay amounts due to Senetek
upon the sale of Cell Line Products in accordance with Section 4.

     7.2 Termination by Senetek. This Agreement may be terminated by Senetek if:
         ----------------------

         (a) Signet shall fail to pay any amounts as provided in Section 4 at
any time when the same become due, and such failure shall continue unremedied
for thirty (30) days after written notice thereof is sent by Senetek to Signet;

         (b) Signet shall at any time become insolvent or make a general
assignment for the benefit of creditors, or if a petition in bankruptcy, or
insolvency, or any reorganization shall be commenced by, against or in respect
of Signet and shall remain undismissed for more than sixty (60) days;

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         (c) In the event of breach or default (for reasons other than failure
to pay any amounts due hereunder) by Signet; provided, however, Senetek shall
give written notice of termination by reason of such default. If such default
shall not be cured within ninety (90) days after written notice, the Agreement
shall be terminated at the end of such ninety (90) day period.

         (d) In the event revenues received by Senetek from Signet from
"Level 1", i.e., payments received from "Current Cell Line Products" hereunder
shall be less than "*Filed Separately with the Commission*" for a period of two
(2) successive years, Senetek has the right to terminate this Agreement with
respect to "Current Cell Line Products" only.

8.       Confidentiality. Signet agrees to keep strictly confidential all
         ---------------
material and other information classified as "Confidential" including, but not
limited to, the terms and conditions of the Basic Agreement/License, and
supplied to Signet by Senetek in connection with its performance under this
Agreement. Signet undertakes not to disclose any such "Confidential" materials
or information to any person except as may be necessary for the furtherance of
this Agreement. Signet further agrees to bind its officers and employees, and
any agents, representatives or third parties who have knowledge of or access to
such "Confidential" information to a similar obligation of confidentiality. In
the event of termination of this Agreement, Signet agrees to return any such
"Confidential" materials or information to Senetek and to cause any person to
whom such "Confidential" materials or information has been supplied to do
likewise.

9.       Governing Law and Arbitration: Venue.
         ------------------------------------

     9.1 This Agreement shall be deemed made under, governed by and construed in
accordance with the laws of the State of California, without giving effect to
conflict of laws provisions thereof. The parties agree that the party to this
Agreement prevailing in an action arising from breach of this Agreement or of
any of its provisions shall be entitled to all costs of such suit or action,
including attorneys' fees.

     9.2 Any controversy or claim arising out of or relating to this Agreement
or the breach thereof, shall be settled by arbitration in San Francisco,
California, in accordance with the Rules of the American Arbitration Association
then obtaining, and judgment upon the award rendered by the arbitrator(s) may be
enforced in either the courts of the State of California or the United States
District Court for the District of California, to whose jurisdiction each of the
parties herby consents. Nothing contained herein shall prevent the parties from
seeking injunctive or other equitable relief in the foregoing courts prior to
arbitration.

10.      General.
         -------

     10.1 In the event any proceeding is commenced to enforce this Agreement or
otherwise relating to this Agreement, the prevailing party shall be entitled to
reasonable attorneys' fees and costs incurred in connection therewith.

     10.2 This Agreement may be executed in one or more counterparts, each of
which shall be deemed an original, but all of which together shall constitute
one and the same instrument; however, this Agreement shall be of no force or
effect until executed by both parties.

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     10.3 Captions and Section and Subsection headings used herein are for
convenience only, and are not a part of this Agreement and shall not be used in
construing it.

     10.4 Each of the parties agrees to execute and deliver such further
documents and to cooperate in such manner as may be necessary to implement and
give effect to the agreements contained herein.

     10.5 This Agreement shall be binding upon and shall inure to the benefit of
each party, its successors and permitted assigns.

     10.6 If any provision of this Agreement, or the application thereof, is
held to be invalid or unenforceable, the remainder of the Agreement shall
continue in full force and effect.

     10.7 The terms of this Agreement shall supersede the terms of any invoice,
confirmation, purchase order or other commercial document of the parties.

     10.8 The parties executing this Agreement warrant that they have the
requisite authority to do so.

     10.9 No waiver by either party of any condition, or of any breach of any
term, covenant, representation or warranty contained in this Agreement, in any
one or more instances, shall be deemed to be construed as a further breach or a
waiver of any other condition or of any breach of any other term, covenant,
representation or warranty.

     10.10 This Agreement sets forth the entire agreement and understanding
between the parties hereto respecting the subject matter hereof, and supersedes
all prior oral discussions and writing between the parties. No modifications,
extension or waiver of this Agreement or any provision thereof shall be binding
unless agreed to in writing by the parties.

     10.11 This Agreement shall inure to the benefit of and be binding upon the
parties and their agents, successors and permitted assigns.

     10.12 For the purpose of all provisions of this Agreement requiring the
giving of notice by either party to the other, notice shall be deemed to be
given when mailed by registered mail, postage prepaid, and sent to the addresses
given below for Signet and Senetek. The notices to Signet should be sent to the
attention of:

     Ronald J. Casciato, President
     Signet Laboratories
     180 Rustcraft Road
     Dedham, Massachusetts 02026

     The notices to Senetek should be sent to the attention of:

     Frank Massino, President
     Senetek PLC
     620 Airpark Road
     Napa, California 94558

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                  IN WITNESS WHEREOF, the respective parties hereto have
executed this Agreement by their fully authorized officers on the date appearing
below their signatures.

                                     Signet Laboratories, Inc.

Date: September 29, 2000             By: /s/ Ronald J. Casciato
      ---------------------              -----------------------------
                                         Ronald J. Casciato, President

                                     Senetek PLC

Date:                                By: /s/ Frank Massino
      ---------------------              -----------------------------
                                         Frank Massino, President

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