<PAGE>   1

                                                                   Exhibit 10.42

                              SETTLEMENT AGREEMENT

Settlement Agreement dated April 13, 1998 by and among with the Company, Windsor
Capital Management, Ltd. and certain other parties thereto.



<PAGE>   2

                              SETTLEMENT AGREEMENT


                THIS SETTLEMENT AGREEMENT is entered into as of this 13th day of
April 1999 by and among SENETEK PLC a company organized under the laws of
England ("Senetek"), SILVER CREEK INVESTMENTS, LTD., a British Virgin Islands
company ("Silver Creek"), BOMOSEEN INVESTMENTS, LTD., a British Virgin Islands
company ("Bomoseen"), ELSTREE HOLDINGS, LTD., a British Virgin Islands company
("Elstree") and DANDELION INVESTMENTS, LTD., a British Virgin Islands company
("Dandelion" and together with Silver Creek, Bomoseen and Elstree, the
"Investors"), WINDSOR CAPITAL MANAGEMENT, LTD., ("Windsor"), AL-SABAH TRADING
AND DEVELOPMENT COMPANY ("Al-Sabah"), THE ALANA GROUP, LTD. ("Alana"), PACKARD,
LTD. ("Packard") and MOHAMED HADID ("Hadid").

                WHEREAS, Senetek and Windsor are parties to a Credit Agreement
dated as of April 28, 1998, as the same may have been amended (the "Credit
Agreement"), pursuant to which Windsor extended to Senetek a line of credit in
the amount of $10,000,000;

                WHEREAS, prior to the date of this Agreement, Senetek borrowed
an aggregate amount of $6,600,000 under the Credit Agreement (the "Borrowings");

                WHEREAS, borrowings under the Credit Agreement do not bear
interest and may be repaid at any time, without penalty, by Senetek;

                WHEREAS, in connection with the Borrowings, Senetek issued to
Windsor a warrant to purchase 1,885,715 ordinary shares of Senetek ("Ordinary
Shares") at a purchase price of $3.50 per share (the "Warrant");

                WHEREAS, subsequent to the issuance of the Warrant, the Warrant
may have been amended to reduce the Warrant exercise price and increase the
number of shares covered by the Warrant but the parties acknowledge that the
documentation of the amendment (if any) is in incomplete and unclear;

                WHEREAS, the Warrant has been exercised by Windsor and Senetek
has issued an aggregate of 2,105,715 Ordinary Shares in respect of the exercise
of the Warrant (the "Warrant Exercise Shares");

                WHEREAS, Windsor currently holds a certificate representing
1,885,715 of the Warrant Exercise Shares (the "Certificate") and the Company
currently holds the certificate representing the remaining Warrant Exercise
Shares;

                WHEREAS, Windsor made no cash payment to Senetek upon the
exercise of the Warrant since Windsor and Senetek intended that the exercise
price payable by Windsor upon exercise of the Warrant would be offset against
and reduce the amount of the Borrowings;



<PAGE>   3

                WHEREAS, the parties hereto desire to enter into this Agreement
for the purpose, among other, of resolving the uncertainty concerning the amount
of the exercise price payable by Windsor upon exercise of the Warrant and the
amount by which the Borrowings have been reduced as a result of the application
of the exercise price to the repayment of the Borrowings;

                WHEREAS, in connection with the execution of the Credit
Agreement, Senetek issued to Windsor warrants to purchase Ordinary Shares for a
price of $6.00 per share which expire by their terms on April 28, 2001 (the
"Additional Warrants");

                WHEREAS, the exercise price of the Additional Warrants may have
been reduced from $6.00 per share to $4.00 per share;

                WHEREAS, the parties agree that the documentation of the
Additional Warrants is incomplete and unclear and does not clearly indicate the
number of the Additional Warrants issued or whether the exercise price of the
Additional Warrants was reduced from $6.00 per share to $4.00 per share;

                WHEREAS, for purposes of resolving the foregoing uncertainty
concerning the Additional Warrants, the parties desire to enter into this
Agreement for the purpose, among others, of recording their agreement that all
of the Additional Warrants have been cancelled and that Senetek will issue to
Windsor, upon the terms and subject to the conditions set forth in this
Agreement, new warrants to purchase 440,000 Ordinary Shares at a purchase price
of $4.00 per share, which new warrants will contain the provisions set forth in
the form of certificate previously representing the Additional Warrants (the
"$4.00 Warrants");

                WHEREAS, the Investors provided Windsor with the funds used by
Windsor to make the initial $6,600,000 loan to Senetek under the Credit
Agreement;

                WHEREAS, Windsor desires to assign to Investors (i) all of its
right, title and interest in and to the Credit Agreement, including the right to
receive repayment of the Borrowings, and (ii) all of its right, title and
interest in and to the Warrant Exercise Shares;

                WHEREAS, in connection with the settlement of the matters
referred to in this Agreement, Senetek is issuing to Investors, concurrently
with the execution of this Agreement, a warrant to purchase an aggregate of
2,261,143 Ordinary Shares at the exercise price specified therein;

                WHEREAS, at or about the time of the execution of this
Agreement, Investors and Senetek are entering into a Securities Purchase
Agreement pursuant to which Investors will provide additional financing to
Senetek through the purchase of securities from Senetek upon the terms set forth
therein ( the "New Financing");

                WHEREAS, a portion of the proceeds from the New Financing will
be applied to repay the Borrowings in full;




<PAGE>   4

                WHEREAS, Al-Sabah and Alana have entered into a Consulting
Agreement with Senetek dated February 20, 1998 (the "Consulting Agreement");

                WHEREAS, the parties desire to enter into this Agreement for the
purpose of documenting their agreement that neither Windsor, Al-Sabah, Alana nor
Hadid nor any affiliate of any of them shall have any right to receive any fee
or other payment pursuant to the Consulting Agreement or any other agreement,
arrangement or understanding on account of the New Financing or the repayment of
the Borrowings;

                WHEREAS, Senetek and Packard, a company affiliated with Hadid,
entered into a letter agreement dated July 10, 1997 (the "Packard Agreement")
pursuant to which Packard agreed to perform certain market research for Senetek;

                WHEREAS, Senetek paid Packard $200,000 (the "Deposit") in
consideration for the anticipated performance by Packard of its obligations
under the Packard Agreement and the preparation of a research report;

                WHEREAS, Packard has not performed its obligations under the
Packard Agreement and Hadid, on behalf of Packard, desires to repay the Deposit
to Senetek by executing and delivering to Senetek the Promissory Note A in the
form attached to this Agreement (the "A Note");

                WHEREAS, Senetek, Packard and Hadid desire to cancel the Packard
Agreement;

                WHEREAS, Al-Sabah, a company affiliated with Hadid, has borrowed
$500,000 from Senetek and the obligation of Al Sabah to repay the $500,000 loan
is evidenced by a promissory note dated September 21, 1998 in the principal
amount of $500,000, bearing interest at the rate of 6% per annum, which is due
and payable to Senetek upon demand by Senetek (the "Promissory Note");

                WHEREAS, Senetek has made a demand for the repayment in full of
the principal amount of and all accrued interest on the Promissory Note;

                WHEREAS, $300,000 of the principal amount of the Promissory Note
has been repaid and Hadid desires to repay, on behalf of Al-Sabah, the balance
owing on the Promissory Note by executing and delivering to Senetek the
Promissory Note B in the form attached to this Agreement (the "B Note");

                WHEREAS, Windsor has invested $3,300,000 in Senetek in
consideration for the issuance of Ordinary Shares, the number of which Senetek
and Windsor agreed to be 1,100,000, subject to adjustment in the event that the
market price for Senetek's American Depositary Shares was less than $5.00 per
American Depositary Share on June 30, 1998;

                WHEREAS, the foregoing agreement to so adjust the number of
shares issued to Windsor was confirmed in a letter dated March 24, 1998 from
Anthony J. Cataldo, the then 




<PAGE>   5

Chairman and Chief Executive Officer of Senetek, to Hadid as the representative
of Windsor (the "March 24 Letter");

                WHEREAS, the market price for Senetek's American Depositary
Shares on June 30, 1998 was less than $5.00 per American Depositary Share and
Senetek and Windsor have agreed that the March 24 Letter would require Senetek
to issue an additional 625,000 Ordinary Shares to Windsor;

                WHEREAS, Senetek desires to issue 625,000 Ordinary Shares in
full satisfaction of its obligations described in the March 24 Letter; and

                WHEREAS, Windsor has assigned its right to receive 378,788 of
the 625,000 Ordinary Shares to Wallington Investments and by executing this
Agreement Windsor hereby confirms such assignment and its instructions to the
Company to issue 378,788 Ordinary Shares to Wallington Investments and to issue
the remaining 246,212 Ordinary Shares to Windsor;

                NOW, THEREFORE, in consideration of the foregoing and for other
good and valuable consideration, the receipt and adequacy of which are hereby
acknowledged, the parties hereto hereby agree as follows:

                SECTION 1. EXERCISE OF WARRANT; REPAYMENT OF BORROWINGS UNDER
THE CREDIT AGREEMENT. The parties hereto agree that immediately prior to the
exercise of the Warrant, the Warrant entitled Windsor, as holder of the Warrant,
to purchase an aggregate of 2,105,715 Ordinary Shares at a purchase price of
$2.00 per share for an aggregate purchase price of $4,211,430 (the "Aggregate
Exercise Price"). The Warrant has been exercised by Windsor in full and Windsor
has been issued the Warrant Exercise Shares. As consideration for the issuance
of the Warrant Exercise Shares and in satisfaction of Windsor's obligation to
pay the Aggregate Exercise Price, the amount of the Borrowings has been reduced
by the Aggregate Exercise Price, with the result that the amount of the
Borrowings outstanding following exercise of the Warrant was and continues to be
$2,388,570 (the "Remaining Loan").

                SECTION 2. ASSIGNMENT; POWER OF ATTORNEY. Windsor hereby assigns
to Investors all of its rights, title and interest in and to, and hereby
relinquishes to Investors any and all rights it may have in, to and under, the
Loan Agreement and the Warrant Exercise Shares, including, without limitation
its right to receive any and all payments in respect of the repayment of the
Remaining Loan. The foregoing assignment is made to the Investors in the
respective amounts set forth on Schedule I hereto. Concurrently herewith,
Windsor is delivering to Kevin McCarthy, as representative of the Investors, the
Certificate. Windsor hereby irrevocably constitutes and appoints Kevin McCarthy
as its attorney-in-fact, with full power of substitution, as its true and lawful
agent and attorney-in-fact, with full power and authority in its name, place and
stead to execute, acknowledge, deliver, file and record stock powers,
assignments, certificates and other instruments and instructions appropriate or
necessary to convey the Warrant Exercise Shares, including the shares
represented by the Certificate, to the Investors in the manner contemplated by
this Agreement, to submit the Certificate to the Company for cancellation, and
to secure the issuance of new certificates in the names of the respective
Investors representing the Warrant 



<PAGE>   6

Exercise Shares or any portion thereof. The foregoing power of attorney is
irrevocable and a special power coupled with an interest. Windsor hereby agrees
to be bound by any act of the foregoing attorney-in-fact taken or made in good
faith pursuant to such power of attorney. Windsor and Hadid hereby represent and
warrant that Windsor has not assigned any of its right, title or interest in, to
or under the Loan Agreement, the Remaining Loan or the Warrant Exercise Shares
to any other person or entity.

                SECTION 3. CANCELLATION OF THE ADDITIONAL WARRANTS. The
Additional Warrants and all amendments thereto and all warrants, if any, issued
in substitution thereof (collectively the "Cancelled Warrants") are hereby
cancelled and shall be of no further force or effect. Windsor and Hadid hereby
represent and warrant that Windsor has not assigned any of its right, title or
interest in the Cancelled Warrants to any other person or entity. Windsor and
the Investors hereby agree that they have no continuing interest in or rights
arising out of any of the Cancelled Warrants. Windsor and Hadid hereby agree to
return promptly to Senetek any and all certificates representing the Cancelled
Warrants.

                SECTION 4. ISSUANCE OF $4.00 WARRANTS. As soon as practicable
following the date of this Agreement, the Company will issue 440,000 $4.00
Warrants to Windsor. The $4.00 Warrants shall provide that if Hadid shall fail
to make, for any reason whatsoever, any payment under the A Note or the B Note
(in any amount) on or prior to the payment date for such payment specified in
the respective A Note or B Note, all 440,000 $4.00 Warrants shall be cancelled
automatically and shall not be reinstated in any manner, even if the payments so
failed to be made shall later be made to the Company.

                SECTION 5. EXECUTION AND DELIVER OF THE A NOTE AND THE B NOTE.
Concurrently herewith, Hadid is executing and delivering the A Note and the B
Note to Senetek. Senetek hereby agrees that upon payment in full of the
principal amount of and all accrued interest, if any, on the A Note, the
$200,000 Deposit shall be deemed to have been repaid to Senetek. Except for the
obligation of Hadid to pay the principal amount of and all accrued interest, if
any, on the A Note in full, Senetek, Packard and Hadid hereby agree that the
Packard Agreement is terminated. Senetek agrees that upon payment in full of the
principal amount of and all accrued interest, if any, on the B Note, the
obligations of Al-Sabah under the Promissory Note shall be satisfied in full.

                SECTION 6. DELIVERY OF CERTIFICATES REPRESENTING AN AGGREGATE OF
625,000 ORDINARY SHARES. As soon as practicable following the date of this
Agreement and in full satisfaction of its obligations under the March 24 Letter,
the Company shall deliver (i) to Wallington Investments, Ltd. ("Wallington") a
certificate issued in the name of Wallington representing 378,788 Ordinary
Shares, and (ii) to Windsor a certificate issued in the name of Windsor
representing 246,212 Ordinary Shares.

                SECTION 7. INVESTMENT REPRESENTATIONS. Windsor and Wallington
(by its execution of the acknowledgement hereto) each hereby represents and
warrants severally as to itself (but not as to the other) that (i) the 246,212
Ordinary Shares or the 378,788 Ordinary Shares, as the case may be, issued to it
and, as to Windsor, the $4.00 Warrants, acquired as 





<PAGE>   7

provided in this Agreement (the "Securities") are being acquired for investment
purposes only for their own respective account and not with a view to the resale
or distribution of any of the Securities in contravention of applicable law,
(ii) it has had an opportunity to ask questions and receive answers from Senetek
regarding the business of Senetek and the investment in the Securities, (iii) it
is experienced in making investments such as an investment in the Securities and
it is able to fend for itself, can bear the economic risk of its investment in
the Securities and has sufficient knowledge and experience in financial and
business matters such that it is capable of evaluating the merits and risks of
an investment in the Securities, and (iv) it is an "accredited investor" within
the meaning of Rule 501 of Regulation D of the Regulations of the SEC under the
Securities Act of 1933, as amended (the "Act"). Windsor and Wallington (by its
execution of the acknowledgement hereto) each acknowledge that it understands
that the Securities are "restricted securities" under the federal securities
laws inasmuch as they are being acquired from Senetek in a transaction not
involving a public offering and that under applicable laws and regulations the
Securities may not be resold without registration under the Act, except in
certain limited circumstances, and each represents that it is familiar with
these resale limitations. In the event the Securities have not been registered
under the Act, Windsor and Wallington (by its execution of the acknowledgement
hereto) each acknowledge that it may not dispose of any portion of the
Securities unless it shall have furnished to Senetek an opinion of counsel, in
form and substance reasonably satisfactory to Senetek, rendered by a law firm
experienced in matters involving the sale of securities under federal and state
securities laws and reasonably satisfactory to Senetek, to the effect that the
disposition will not require registration of the Securities under the Act or
registration or qualification under any state securities or "blue sky" law.

                SECTION 8. LEGENDS. Windsor and Wallington (by its execution of
the acknowledgement hereto) each acknowledge that it understands that the
certificates evidencing the Securities (or the American Depositary Receipts
evidencing the American Depositary Shares representing the Securities) may bear
a legend in substantially the following form:

                THESE SECURITIES HAVE NOT BEEN REGISTERED UNDER THE SECURITIES
                ACT OF 1933, AS AMENDED (THE "ACT") OR ANY APPLICABLE STATE
                SECURITIES LAWS. THEY MAY NOT BE SOLD, OFFERED FOR SALE, PLEDGED
                OR HYPOTHECATED IN THE ABSENCE OF A REGISTRATION STATEMENT IN
                EFFECT WITH RESPECT TO THE SECURITIES UNDER THE ACT AND THE
                REGISTRATION OR QUALIFICATION OF THE SECURITIES UNDER APPLICABLE
                STATE SECURITIES LAWS OR AN OPINION OF COUNSEL REASONABLY
                SATISFACTORY TO SENETEK, IN FORM AND CONTENT REASONABLY
                SATISFACTORY TO SENETEK, THAT SUCH REGISTRATION OR QUALIFICATION
                UNDER THE ACT AND STATE SECURITIES LAWS IS NOT REQUIRED.

                SECTION 9. NO FEES. Windsor, Al-Sabah, Alana and Hadid hereby
acknowledge and agree that neither they nor any person controlling, controlled
by or under common control 




<PAGE>   8

with any of them are or shall be entitled to receive from Senetek or any other
party any fee or other payment (whether in the form of cash, warrants or other
securities or property) pursuant to the Consulting Agreement or any other
agreement, arrangement or understanding, on account of or arising out of the New
Financing or the repayment of the Borrowings or the Remaining Loan.

                SECTION 10. AUTHORITY OF HADID. Hadid hereby represents to
Senetek and the Investors that he has the full power and authority to enter into
this Agreement on behalf of Windsor, Al-Sabah, Packard and Alana and to bind
Windsor, Al-Sabah, Packard and Alana to the terms of this Agreement.

                SECTION 11. FURTHER ASSURANCES. Each party of this Agreement
agrees to execute and deliver such further documents and instruments and take
such further action as any other party to this Agreement may reasonably request
for the purpose of further documenting the agreements set forth herein or
otherwise carrying out the intent of this Agreement.

                SECTION 12. GOVERNING LAW. This Agreement, the A Note and the B
Note shall be governed by and construed in accordance with the laws of the State
of California without regard to conflict of laws principles.

                SECTION 13. ENTIRE AGREEMENT. This Agreement constitutes the
entire agreement among the parties hereto pertaining to the subject matter of
this Agreement and supersedes all prior agreements, understandings, negotiations
and discussions, whether oral or written, of the parties.

                SECTION 14. AMENDMENTS AND WAIVERS. No amendment, supplement,
modification or waiver of this Agreement shall be binding unless set forth in a
writing executed by the party to be bound thereby. No waiver of any provision of
this Agreement shall be deemed to constitute or shall constitute a waiver of any
other provision hereof (whether or not similar), nor shall any such waiver
constitute a continuing waiver unless otherwise expressly provided in the
waiver.

                SECTION 15. COUNTERPARTS. 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.

                SECTION 16. HEADINGS. The heading of the sections in this
Agreement are inserted for convenience of reference only and shall not be deemed
to be a part of or to affect the meaning or interpretation of any provision of
this Agreement.




<PAGE>   9

                IN WITNESS WHEREOF, the parties hereto have entered into this
Agreement, or have caused this Agreement to be duly executed on their behalf by
their respective authorized representatives, as of the day and year first above
written.

SENETEK, PLC                            AL-SABAH TRADING AND 
                                        DEVELOPMENT COMPANY

By /s/ Frank J. Massino                 By /s/ Mohamed Hadid
   -------------------------------        --------------------------------------
   Frank J. Massino                       Mohamed Hadid
   Chief Executive Officer                Authorized Signatory


WINDSOR CAPITAL MANAGEMENT, LTD.        THE ALANA GROUP, LTD.

By /s/ Mohamed Hadid                    By /s/ Mohamed Hadid
   -------------------------------        --------------------------------------
   Mohamed Hadid                          Mohamed Hadid
   Authorized Signatory                   Authorized Signatory


PACKARD, LTD.

By /s/ Mohamed Hadid                       /s/ Mohamed Hadid
   -------------------------------      ----------------------------------------
   Mohamed Hadid                          MOHAMED HADID
   Authorized Signatory                   


SILVER CREEK INVESTMENTS, LTD.          BOMOSEEN INVESTMENTS, LTD.

By /s/ Silver Creek Investments, Ltd.   By /s/ Bomoseen Investments, Ltd.
   -------------------------------        --------------------------------------
   Name:                                  Name:
   Title:                                 Title:


ELSTREE HOLDING, LTD.                   DANDELION INVESTMENTS, LTD.

By /s/ Elstree Holding, Ltd.            By /s/ Dandelion Investments, Ltd.
   -------------------------------        --------------------------------------
   Name:                                  Name:
   Title:                                 Title:


THE UNDERSIGNED HEREBY ACKNOWLEDGES THIS AGREEMENT FOR THE PURPOSES SPECIFIED IN
SECTIONS 7 AND 8 OF THIS AGREEMENT ONLY:

WALLINGTON INVESTMENTS

By /s/ Wallington Investments
   -------------------------------
   Name:
   Title:



 
<PAGE>   10


                                   SCHEDULE I

                The assignment made by Windsor pursuant to Section 2 of the
Settlement Agreement to which this Schedule I is attached is being made to the
following Investors in the following amounts:

<TABLE>
<CAPTION>
                                    Percentage Interest in the          Number of Warrant
            Investor               Loan Agreement Assigned (1)       Exercise Shares Assigned
            --------               ---------------------------       ------------------------
<S>                                           <C>                            <C>    
Silver Creek Investments, Ltd.                29.74%                         626,269

Bomoseen Investments, Ltd.                    29.74%                         626,269

Elstree Holdings, Ltd.                        20.26%                         426,589

Dandelion Investments, Ltd.                   20.26%                         426,588
</TABLE>


(1)     Includes interest in the right to receive repayment of the Remaining
        Loan.



<PAGE>   11

                                PROMISSORY NOTE A



                                                         Los Angeles, California
                                                                  April 13, 1999



FOR VALUE RECEIVED, the undersigned, MOHAMED HADID, does hereby promise to
        pay to SENETEK PLC, a company organized under the laws of England, at
        its office located at 620 Airpark Road, Napa, California, the following
        amounts on or before the following dates:

<TABLE>
<CAPTION>
                            Payment Date                  Payment Amount
                          -----------------               --------------
<S>                                                          <C>    
                             May 3, 1999                     $40,000

                            June 1, 1999                      40,000

                            July 1, 1999                      40,000

                           August 2, 1999                     40,000

                          September 1, 1999                   40,000

                           October 1, 1999                    15,000
</TABLE>

If any of the foregoing amounts shall not be paid in full on or prior to
        the respective payment date set forth above, the unpaid portion shall
        bear interest commencing on the respective payment date and continuing
        until the unpaid amount shall have been paid in full (together with all
        accrued interest thereon) at the rate of 10% per annum.




                                        /s/ Mohamed Hadid
                                        ----------------------------------------
                                        MOHAMED HADID



<PAGE>   12

                                PROMISSORY NOTE B


                                                         Los Angeles, California
                                                                  April 13, 1999

FOR VALUE RECEIVED, the undersigned, MOHAMED HADID, does hereby promise to
        pay to SENETEK PLC, a company organized under the laws of England, at
        its office located at 620 Airpark Road, Napa, California, the following
        amounts on or before the following dates:

<TABLE>
<CAPTION>
                            Payment Date                  Payment Amount
                          -----------------               --------------
<S>                                                          <C>    
                             May 3, 1999                     $40,000

                            June 1, 1999                      40,000

                            July 1, 1999                      40,000

                           August 2, 1999                     40,000

                          September 1, 1999                   40,000

                           October 1, 1999                    15,000
</TABLE>

If any of the foregoing amounts shall not be paid in full on or prior to
        the respective payment date set forth above, the unpaid portion shall
        bear interest commencing on the respective payment date and continuing
        until the unpaid amount shall have been paid in full (together with all
        accrued interest thereon) at the rate of 10% per annum.




                                        /s/ Mohamed Hadid
                                        ----------------------------------------
                                        MOHAMED HADID



<PAGE>   13

                                PROMISSORY NOTE A



                                                         Los Angeles, California
                                                                  April 13, 1999



FOR VALUE RECEIVED, the undersigned, MOHAMED HADID, does hereby promise to pay
        to SENETEK PLC, a company organized under the laws of England, at its
        office located at 620 Airpark Road, Napa, California, the following
        amounts on or before the following dates:

<TABLE>
<CAPTION>
                            Payment Date                  Payment Amount
                          -----------------               --------------
<S>                                                          <C>    
                             May 3, 1999                     $40,000

                            June 1, 1999                      40,000

                            July 1, 1999                      40,000

                           August 2, 1999                     40,000

                          September 1, 1999                   40,000

                           October 1, 1999                    15,000
</TABLE>

If any of the foregoing amounts shall not be paid in full on or prior to the
        respective payment date set forth above, the unpaid portion shall bear
        interest commencing on the respective payment date and continuing until
        the unpaid amount shall have been paid in full (together with all
        accrued interest thereon) at the rate of 10% per annum.


                                        /s/ Mohamed Hadid
                                        ----------------------------------------
                                        MOHAMED HADID



<PAGE>   14

                                PROMISSORY NOTE B



                                                         Los Angeles, California
                                                                  April 13, 1999



FOR VALUE RECEIVED, the undersigned, MOHAMED HADID, does hereby promise to pay
        to SENETEK PLC, a company organized under the laws of England, at its
        office located at 620 Airpark Road, Napa, California, the following
        amounts on or before the following dates:

<TABLE>
<CAPTION>
                            Payment Date                  Payment Amount
                          -----------------               --------------
<S>                                                          <C>    
                             May 3, 1999                     $40,000

                            June 1, 1999                      40,000

                            July 1, 1999                      40,000

                           August 2, 1999                     40,000

                          September 1, 1999                   40,000

                           October 1, 1999                    15,000
</TABLE>

If any of the foregoing amounts shall not be paid in full on or prior to the 
        respective payment date set forth above, the unpaid portion shall bear
        interest commencing on the respective payment date and continuing until
        the unpaid amount shall have been paid in full (together with all
        accrued interest thereon) at the rate of 10% per annum.




                                        /s/ Mohamed Hadid
                                        ----------------------------------------
                                        MOHAMED HADID