<PAGE>   1
                                                                   Exhibit 10.38




                       SERVICE AGREEMENTS WITH THE COMPANY





Service Agreement dated June 30, 1997 between with the Company and Dr G. Homan




                                       31
<PAGE>   2
                          EXECUTIVE OFFICER'S AGREEMENT


AN AGREEMENT made the 30th day of June 1997.


                                     BETWEEN

SENETEK PLC ("the Company") whose registered office is situated at 23 Palace
Street, London SW1E 5HW, and

GERLOF HOMAN of 1819 Hermitage Place, Imperial, Missouri 63052, USA ("the
Executive").

WHEREAS the Company employs the Executive and the Executive serves the Company
as the Company's Chief Scientific Advisor pursuant to Letter Agreement dated
April 8, 1997, such Letter Agreement incorporating certain elements of a Service
Agreement dated August 11, 1995, ("the Existing Agreements") the Company and the
Executive have agreed that the Existing Agreements shall be superseded in their
entirety by this present Agreement of June 30, 1997.

NOW IT IS HEREBY AGREED that the Company shall employ the Executive and the
Executive shall serve the Company as its Chief Scientist reporting to the
Company's Chief Executive Officer with effect from June 1, 1997, upon and
subject to the following terms and conditions:

1.       In this Agreement:

         (a)      the expression "the Board" means the Board of Directors for
                  the time being of the Company.

         (b)      the expression "Subsidiary" means a subsidiary (as defined by
                  Section 736 of the UK Companies Act 1985) for the time being
                  of the Company.

         (c)      the expression "associated Company" means in relation to a
                  company, its holding company (as defined by Section 736 of the
                  UK Companies Act 1985) or any subsidiary of such holding
                  company.

         (d)      the expression "the Group" means the Company and any
                  subsidiaries of the Company.

         (e)      any reference to a statutory provision shall be deemed to
                  include a reference to any statutory modification or
                  re-enactment of the same.

2.       The employment shall be for a fixed period from June 1, 1997 to
         December 31, 1999, and shall be subject to termination as hereinafter
         provided.

3.       (a)      The remuneration of the Executive shall be a salary (which
                  shall accrue from day to day) at a rate of US$200,000 per
                  annum. Such salary shall be payable by equal monthly
                  installments on the last day of every month and the first of
                  such payments shall be due with effect from June 30, 1997. The
                  over-all remuneration (which term shall also include the cost
                  to the Company of the total benefits enjoyed by the Executive)
                  of the Executive shall be subject to review by the Company's
                  Compensation Committee during the first quarter of each of the
                  Company's fiscal years and the Compensation Committee shall
                  decide what, if any, increase in the said over-all
                  remuneration shall apply to the fiscal year in question.

         (b)      The Executive shall be entitled to and the Company shall
                  effect payment of a health insurance policy for the benefit of
                  the Executive, his spouse and his immediate family with Blue
                  Cross/BUPA or a similar organization offering equivalent
                  benefits. Such policy to be reviewed and sanctioned by the
                  Company prior to each renewal date.

<PAGE>   3
         (c)      The Executive shall be entitled to participate in the
                  Company's Number 1 Executive Share Option Scheme for Employees
                  ("the Option Scheme") under the terms and conditions of that
                  scheme and shall be granted Options to subscribe for shares of
                  the Company in accordance with the Schedule attached hereto.
                  The grant of options listed on the said Schedule shall be in
                  addition to the Executive's existing option entitlements, the
                  rights to which shall remain in full force and effect. The
                  Company hereby confirms that the Board has undertaken to
                  exercise its discretion in favor of the Executive under Clause
                  4. (1), (2) (a) & (b), and (4)(a) & (b), of the Option Scheme
                  in connection with the Executive's right of conversion of his
                  option entitlements into shares and the subsequent sale of the
                  said shares subject only to (i) the termination of this
                  Executive Agreement for cause as provided in Clause 6(b)
                  below, and (ii) compliance with the relevant provisions of
                  Rule 144 of the US Securities Act of 1933, as amended.

         (d)      During the period of his employment, the Company will effect
                  insurance cover on the life of the Executive in the sum of
                  US$500,000, expressed in favour of the Executive's dependants
                  or as he may direct, on a term basis only. Such cover to be
                  reviewed and sanctioned by the Company prior to each renewal
                  date.

         (e)      The Company may request the Executive to work at such
                  locations or offices of the Company, its subsidiaries or
                  associated companies as it may identify, but the Executive
                  shall be under no obligation to move from his existing
                  location.

         (f)      There are no fixed hours of work.

4.       The Company will provide the Executive with a car allowance of US$750
         per month, from which the Executive shall meet all costs relating to
         his use of whatever vehicle he may decide to utilise.

5.       The Company shall reimburse the Executive all reasonable hotel and
         other expenses wholly and exclusively incurred by him in or about the
         performance of his duties.

6.       (a)      In the case of illness of the Executive or other cause
                  incapacitating him from attending to his duties, the Executive
                  shall continue to be paid during such absence provided that if
                  such absence shall aggregate in all thirteen weeks in any
                  twenty-six consecutive weeks, the Company may terminate the
                  employment of the Executive hereunder by notice given on the
                  date not more than fourteen days after the end of the last of
                  such thirteen weeks. In this event the Executive shall be paid
                  6 months salary in lieu of notice.

         (b)      Termination for cause. The Company shall not be obligated to
                  pay or provide for any compensation or other benefits to the
                  Executive or give effect to any rights for the exercise of
                  options for any period after termination for cause. For the
                  purposes of this Agreement, "cause" shall mean termination for
                  personal dishonesty, wilful misconduct, breach of fiduciary
                  duty involving personal profit, wilful material violation of
                  any law, rule or regulation or material breach of any
                  provision of this Agreement.

7.       The Executive shall (in addition to the usual public and bank holidays)
         be entitled to four weeks holiday in each year to be taken at a time or
         times convenient to the Company. Any vacation not taken during the 12
         month period to December 31 of each year shall lapse and shall not be
         carried forward. No payment shall be made in lieu of vacation time not
         taken.

8.       During the continuance of his employment hereunder, the Executive
         shall, unless prevented by ill health, do all in his power to promote,
         develop, and extend the business of the Group and shall at all times
         and in all respects conform to and comply with the directions and
         regulations made by the Board and also shall not, without the previous
         consent of the Board, engage in any other business of a similar nature
         to or competitive with that carried on by the Group.

<PAGE>   4
9.       Any invention, discovery or improvement upon or in addition to any of
         the Company's inventions made by the Executive during the period of
         employment shall be forthwith communicated to the Company and shall be
         the absolute property of the Group and at the request of the Company
         the Executive shall give and supply all information, know-how and data
         as may be requisite to enable the Group to exploit such invention,
         discovery or improvement and shall execute and do all documents and
         things as may be necessary or desirable for obtaining patent or similar
         protection for the same in any parts of the world as may be specified
         by the Company and for vesting the same in the Group as it may direct.

10.      The Executive shall not (except in the proper course of his duties
         hereunder) either during or after the period of his employment
         hereunder, divulge to any person and shall use his best endeavors to
         prevent the publication or disclosure of any trade secret or
         manufacturing process or any information concerning the business or
         finances of the Group or any of its dealings, transactions or affairs
         or any trade secret or secret manufacturing process of any such
         confidential information governing the Group and all notes and
         memoranda of such trade secrets or information made or received by the
         Executive during the course of his employment hereunder shall be the
         property of the Company and shall be surrendered by the Executive or
         someone duly authorized in that behalf at the termination of his
         employment or at the request of the Board at any time during the course
         of his employment.

11.      The Executive hereby covenants with the Company that he will not,
         within 2 years after ceasing to be employed hereunder, without the
         consent of the Company in writing under the hand of a Director duly
         authorized by a resolution of the Board, directly or indirectly seek to
         procure orders from or do business with any person, firm, or company
         who, on the date of the Executive ceasing to be employed hereunder or
         at any time in the twelve months prior to that date, was a client or
         customer of the Group and with whom in the course of his employment,
         the Executive shall have had dealings, provided always, that nothing in
         this clause contained shall be deemed to prohibit the seeking or
         procuring of orders or the doing of business not in direct or indirect
         competition with the business or businesses conducted by the Group.

12.      This Agreement shall not be terminated by any:

         (a)      merger or consolidation where the Company is not the
                  consolidating or surviving entity; or

         (b)      transfer of all or a substantial majority of the assets of the
                  Company.

         (c)      acquisition or control of 50 per cent or more of the Company's
                  issued and voting equity share capital by any party, or by
                  parties acting in concert or under common control.

         In the event of any such merger or consolidation or transfer of all or
         a substantial majority of the assets of the Company or acquisition or
         control of 50 per cent or more of the Company's issued and voting
         equity share capital by any party, or by parties acting in concert or
         under common control, the surviving or resulting entity or the
         transferee or transferees of the Company's assets or its issued and
         voting equity share capital shall be bound by, and shall have the
         benefit of, the provisions of this Agreement, and the Company shall
         endeavor to take all actions necessary to ensure that such entity or
         transferee or transferees is bound by the provisions of the Agreement.
         Moreover, in the event of such merger or consolidation, or transfer of
         all or a substantial majority of the assets of the Company or
         acquisition or control of 50 per cent or more of the Company's issued
         and voting equity share capital as aforesaid, the Executive may at his
         option at any time continue his employment under the terms and
         conditions of this Agreement, or upon giving not less than 28 days
         Notice at any time, by registered mail, to the registered office of the
         Company, require the Company to effect full settlement of all of the
         Executive's entitlements under the terms and conditions of this
         Agreement, which settlement shall also include the payment of his
         remuneration for the full term of the Agreement and the right to
         convert any and all Option entitlements, (whether such Options be
         vested or not) up to and including December 31, 1999 and the Company
         shall effect full and final settlement within 28 days of receiving the
         said Notice from the Executive.
<PAGE>   5

13.      There is no pension payable, and there is no contracting out
         certificate in force in respect of the Executive's employment
         hereunder.

14.      There are no disciplinary rules or grievance procedures in place in
         relation to the Executive's employment hereunder. The Executive may
         raise any grievance or concern about any disciplinary matter with the
         Board.

15.      This Agreement shall be construed and governed in accordance with and
         under the laws of the State of Missouri applicable to agreements made
         and to be performed in such State.

                              ********************

Signed by                                   }
for and on behalf of                        }          .........................
SENETEK PLC in the presence                 }          PAUL A. LOGAN
of:


Witness

Signed by                                   }
GERLOF HOMAN                                }          .........................
in the presence of:                         }          GERLOF HOMAN


Witness




                                    SCHEDULE


<TABLE>
<CAPTION>
  NO. OF OPTIONS GRANTED     CONVERSION SECURITY               CONVERSION PRICE         VESTING DATE

<S>       <C>                <C>                                  <C>                 <C> 
          50,000             5p Ordinary shares of                 US$1.50            December 31, 1997
                             Senetek PLC

          50,000             5p Ordinary shares of                 US$1.50            December 31, 1998
                             Senetek PLC
                             5p Ordinary shares of
          50,000             Senetek PLC                           US$1.50            December 31, 1999
</TABLE>