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DATED                               3rd July                              1996







                          SENETEK PLC            (1)

                          PAUL ANTHONY LOGAN     (2)













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

                             SUPPLEMENTAL AGREEMENT

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













                                Trowers & Hamlins

                                  6 New Square

                                  Lincoln's Inn

                                 London WC2A 3RP




                                      
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THIS AGREEMENT is made the 3rd day of July 1996

BETWEEN

(1)      SENETEK PLC a company  registered in England under Number 1759068 whose
         registered  office is  situateD at 23 Palace  Street,  London SW1E 5HW,
         England (the "Company"); and

(2)      PAUL ANTHONY LOGAN of 30 Riverside  Drive,  Esher,  Surrey KT10 8PG 
         (the "Executive").

WHEREAS

This Agreement is  supplemental to an executive  officer's  agreement dated 11th
August 1995 between the Company and the Executive (the "Executive Agreement"), a
consultancy agreement dated 2nd March 1992 between the Company and the Executive
(the  "Consultancy  Agreement")  and a letter  dated 11th  August  1995 from the
Company  to  the  Executive  in  relation  to  the  Consultancy  Agreement  (the
"Letter").

NOW IT IS HEREBY AGREED as follows:

1.       The Company and the Executive hereby agree that upon expiry of the term
         of the Executive  Agreement (that is to say, on 1st September 1997) the
         Company shall  continue to employ the Executive for a period until 30th
         September  1998  subject  to and  in  accordance  with  the  terms  and
         conditions of the Executive Agreement except that:

         (a)      During the period from 1st  September  1997 to 30th  September
                  1998 (the  "Additional  Period") the Executive  shall,  unless
                  prevented by ill-health, devote such time and attention to the
                  business of the Company as the Board may require, subject to a
                  maximum  commitment  of a  total  of  fifty  days  during  the
                  Additional  Period  (on  such  days  as the  Company  and  the
                  Executive may from time to time agree).

         (b)      To the extent  that it may  reasonably  be  necessary  for the
                  Executive  to devote more than fifty days  service  during the
                  Additional  Period,  the  Executive may provide to the Company
                  details of the additional  time expended and the nature of the
                  work undertaken and in such circumstances shall be entitled in
                  respect of such additional  time worked to additional  payment
                  at a rate pro rata to his basic remuneration in respect of the
                  Additional Period.

         (c)      The  Executive  shall be obliged  to retire on 30th  September
                  1998  and  the  Company  shall  not  continue  or  extend  the
                  Executive Agreement beyond that date.




                                       
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         (d)      At the  commencement of the Additional  Period,  the Executive
                  shall be entitled  to a salary pro rata to the salary  payable
                  to him immediately  prior to 1st September 1997 and his salary
                  payable to him immediately prior to 1st September 1997 and his
                  salary during the Additional Period shall be subject to review
                  in  accordance  with Clause 3 of the  Executive  Agreement and
                  such salary  shall be paid to the  Executive  irrespective  of
                  whether or not the Company  requires the Executive to work for
                  the entire 50 day period referred to above.  For the avoidance
                  of doubt,  during the  Additional  Period the Executive  shall
                  continue to be entitled to all other benefits and entitlements
                  (except  for  the 4  weeks  holiday  entitlement)  due  to the
                  Executive  under,  pursuant  to  or  in  connection  with  the
                  Executive Agreement.

2.       The Company and the Executive  hereby agree that the  references in the
         Letter to the expiry of the term of the  Executive  Agreement  shall be
         construed  as  references  to the  expiry of the term of the  Executive
         Agreement as amended by this Agreement.

3.       The Company and the Executive hereby agree that the Executive Agreement
         shall be read and construed in accordance with the provisions of Clause
         1 of this  Agreement  and in the  event  of any  conflict  between  the
         provisions  of this  Agreement and the  Executive  Agreement  then this
         Agreement shall prevail.

4.       The parties hereby agree that the Executive Agreement as amended hereby
         shall continue in full force and effect in accordance with its terms.



SIGNED by [G. HOMAN] for and        )
and on behalf of SENETEK PLC        )   /s/ Gerlof Homan
in the presence of:                 )



                               Nancy K. Dennigmann
                               1714 Sibley Street
                              St. Charles, MO 63301



SIGNED by the said                   )
PAUL ANTHONY LOGAN                   )   /s/ P. A. Logan
in the presence of:                  )






                                       2
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Signature of Witness:      /s/ Karen Goldsmith

Full name of Witness:      Karen Goldsmith

Address:                   5 Charlton Drive
                           Biggin Hill
                           Kent TN16 3TZ

Occupation:                PA






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SENETEK PLC
                                       SENESCENCE TECHNOLOGY
23 PALACE STREET, LONDON S1E5HW
(Registered Office)
Tel: 0171-828-4800  Fax: 0171-828-8081


August 11, 1995

Paul Logan, Esq.
30 Riverside Drive
Esher, Surrey KT10 8PG
England

Dear Mr. Logan:

We refer to the executive  officer's  agreement between Senetek PLC and yourself
dated September 1, 1989 (the "First Executive  Officer's  Agreement") and to the
consultancy   agreement  between  us  dated  March  2,  1992  (the  "Consultancy
Agreement").

As you are aware, the Consultancy Agreement was entered into between us in order
to take effect upon the expiry of the First Executive Officer's Agreement,  with
effect from September 1, 1992. However, further to an earlier reconsideration of
these  arrangements  it has  been  agreed  that  the  commencement  date  of the
Consultancy  Agreement be deferred until the expiry of the term of the executive
officer's agreement dated 11th August 1995 made between Senetek PLC and yourself
(the "New Executive  Officer's  Agreement"),  regardless of earlier  termination
howsoever occasioned.  Notwithstanding the foregoing,  in the event that the New
Executive Officer's Agreement shall terminate prior to the end of its fixed term
by reason of your serving  three months  notice  pursuant to Clause 2 of the New
Executive Officer's Agreement,  the Consultancy  Agreement shall commence on the
expiry  of the  said  three  month  notice  period.  In the  event  that the New
Executive Officer's Agreement shall terminate prior to the end of its fixed term
by reason of  termination  pursuant to Clause 6 of the New  Executive  Officer's
Agreement,  the Consultancy  Agreement  shall commence six months  following the
date of termination.

Upon  commencement,  the Consultancy  Agreement shall thereafter  continue for a
period of three years from such date in accordance with its terms.

Please  confirm  your  agreement to and  acceptance  of the above by signing and
returning the enclosed duplicate of this letter.

Yours sincerely,                                            Accepted by:


/s/ Gerlof Homan                           /s/ P. A. Logan
____________________________            __________________________________
Chairman and Chief Executive            P.A. Logan
Officer For and on behalf of  
Senetek PLC