<PAGE>   1
                                                                   EXHIBIT 10.21



                              EMPLOYMENT AGREEMENT



        THIS AGREEMENT is made effective on June 1, 1998 between HYPERBARIC
SYSTEMS, whose address is 1127 Harker Avenue, Palo Alto, CA 94301, incorporated
under the laws of the State of California, hereinafter called "EMPLOYER", or
"COMPANY" and VLADIMIR SEREBRENNIKOV, whose address is Academgorodok 1A, Apt 53,
Krasnoyark, Russia 660036 hereinafter called "EMPLOYEE".

                                   WITNESSETH:

               1. PURPOSE OF AGREEMENT. HYPERBARIC SYSTEMS is a duly established
California corporation engaged in the business of designing, manufacturing and
marketing products for the medical, food and semiconductor industries, and
EMPLOYEE represents that he has technical expertise in the development of
preservation systems. This agreement between EMPLOYER and EMPLOYEE is entered
into for the purpose of defining the relationship, responsibilities, and
agreement between EMPLOYER and EMPLOYEE.

               2. EMPLOYMENT: EMPLOYER hereby employs VLADIMIR SEREBRENNIKOV as
the Company's Technical Director of Preservation Systems.

               3. EMPLOYEE DUTIES AND RESPONSIBILITIES. EMPLOYEE shall be
employed as Technical Director of Preservation Systems with the following duties
and responsibilities:

                      a. Direct all technical research and development efforts
                      of the COMPANY regarding preservation systems, reporting
                      to the Branch Chief and as directed by the President.

                      b. Assure that all chamber designs and testing of
                      platelets and other future products are done according to
                      specifications approved by the Company, and operate within
                      the specified limits.

                      c. Develop new products and technologies as directed by
                      the Company plan, under the direction of the Branch Chief
                      and President.

<PAGE>   2

                      d. Assure that all schedules and milestones under the
                      Technical Director's control are carried out within the
                      agreed time frames.

                      e. Provide a complete technical activity/progress report
                      including test results conducted at the Branch and other
                      locations under the Branch's control on a monthly basis
                      and as requested by the Branch Chief or the President.
                      Report directly and immediately to the President any
                      significant results that may impact the business of the
                      Company, including unfavorable test results or technical
                      delays.

                      f. Perform other tasks and become involved in projects as
                      directed by the President.

               4. EMPLOYEE'S PERFORMANCE. EMPLOYEE shall work as agreed upon by
the parties. Employee agrees to devote his best efforts to the Corporation's
business and devote his efforts to the Corporation for the performance of his
duties as Technical Director of Preservation Systems, and perform other duties
and responsibilities as directed by the President.

               5. INVENTIONS AND PATENTS. EMPLOYEE agrees that all rights to
inventions and patents derived while employed by EMPLOYER shall be the property
of the COMPANY and all necessary steps to transfer such rights, if required
under U.S. laws, shall be executed by EMPLOYEE.

               6. TERM. The term of this Agreement shall be effective for a
period of one year from the date of signing of this agreement. It is the intent
of the parties that this contract shall continue indefinitely until terminated
by either party. Upon the expiration of the Term of this Agreement, it may be
terminated with thirty days written notice by either party.

               7. COMPENSATION. For the services rendered by EMPLOYEE hereunder,
EMPLOYEE shall be compensated initially at an amount of $400 per month, but may
be adjusted as agreed to by the parties. Payment shall be made in Rubles based
on the Central Bank of the Russian Federation's prevailing exchange rate in
effect at the time of payment.

<PAGE>   3
               8. BONUS. A bonus amount of $25,000 shall be paid to EMPLOYEE
upon the successful completion of all of the Phase I milestones within the
agreed time frame. These milestones shall consist of the following items:

               a.   Successfully complete Platelet experiments according to
                    protocols and conditions provided by the COMPANY. All
                    documentation of test results shall be delivered in writing
                    at the conclusion of the tests.

               b.   Deliver to the COMPANY all published and unpublished
                    articles that relate to the invention within two weeks from
                    the establishment of the Branch.

               c.   Deliver to the COMPANY all patent information necessary for
                    the COMPANY'S legal counsel to render an opinion that one or
                    more U.S. patents for the container and/or the technology
                    are likely to be granted.

               d.   A legal opinion by the COMPANY'S legal counsel that the
                    invention is likely to be granted a U.S. patent. This should
                    be accomplished within 30 days from the date that all
                    relevant documents are delivered to the COMPANY.

               e.   Deliver to the COMPANY a working container for testing
                    Platelets.

               f.   Sign a non-compete agreement.

               g.   Additional bonus and incentives for milestones (to be
                    defined at a future date) successfully completed for other
                    blood products, organs, verification and semiconductors
                    technology will be negotiated under a separate incentive
                    program agreement.

               h.   Sign a non-compete agreement.

               9. ASSIGNMENT AND PROSPECTIVE WORK. The EMPLOYEE shall assign all
the rights to all intellectual property created by EMPLOYEE according to the
AGREEMENT ON ASSIGNMENT OF PATENT AND TECHNOLOGY, signed between the parties,
which shall be an integral part of this Agreement.

               10. DURATION OF WORKING TIME. A five day work week shall be
established for EMPLOYEE according to the Code of Labor Laws of the Russian
Federation (COLL RF).

<PAGE>   4

               11. HOLIDAYS. Work shall not be required on the following
holidays:

               1-2 January - New Year

               7 January - Christmas

               8 March - International Women Day

               1-2 May - Holiday of Spring and May

               9 May - Day of Victory

               12 June - Day of Acceptance of Declaration on State Sovereignty
of the Russian Federation

               7 November - Anniversary of Great October Social revolution

               12. VACATION. EMPLOYEE shall be entitled to annual paid vacations
of four weeks per year in view of six-days work week, after the first 11 months
of service.

               13. GUARANTEES AND COMPENSATION FOR BUSINESS TRIPS. The EMPLOYEE
shall have the right to cover expenses and receive other compensation in view of
business trips within the following rates:

               a)   Business Trips to Rural Place:

               -    Daily allowance for the period of the business trip -
                    $12/day

               -    Rent Payment - Up to $35/day

               b)   Business Trip to Cities of the RF

               -    Daily allowance - $15/day

               -    Rent Payment - Up to $35/day

               c)   Business Trips to Moscow, St. Petersburg, Capitals of the
                    Republics, incorporated into the RF, Regional or Territorial
                    Centers including cities with 1 million population:

               -    Daily allowance - $35/day

               -    Rent Payment - Up to $90/day

               d)   Business Trips to Western Europe, Canada, USA:

               -    Daily allowance - $70/day

<PAGE>   5

               -    Rent Payment - Up to $150/day

               Rent payments shall be effected on those actual expenses paid
               with receipts(bills), and checks, but shall not exceed the
               aforementioned rates.

               Daily payment is to be effected according to the aforementioned
               rates in view that the arrival and departure days are considered
               as 2 days.

               Any changes to the aforementioned rates is possible only upon the
               written instruction or approval of the President.

               Compensation of return fare shall be effected for actual expenses
               upon submission of tickets or other documents justifying such
               expenses.

               Any other regulations, guarantees and compensations on business
               trips are to be effected in accordance with COLL RF.

               14. COMPENSATION FOR WEAR OF INSTRUMENTS, EQUIPMENT AND TRANSPORT
THAT IS THE PROPERTY OF THE EMPLOYEE. The EMPLOYEE shall have he right to
receive compensation for wear of the instruments, equipment and transport when
using these for the benefit of the Company. Amounts and terms of the
compensation shall be stipulated by a separate agreement between EMPLOYEE and
Company.

               15. TERMINATION UPON BREACH. This Agreement shall be terminated
upon material breach of any of the provisions herein, or breach of the material
provisions of any and all supplemental agreements which the EMPLOYEE and
EMPLOYER may mutually execute.

               16. CONFIDENTIALITY AGREEMENT. EMPLOYEE agrees that all
information made available to EMPLOYEE regarding the products, clients and
software systems of EMPLOYER are confidential and require a high degree of
confidentiality so as not to violate the rights of others and to prevent the use
thereof for purposes detrimental to the interests of EMPLOYER and its clients.
Such information in any form shall be hereinafter referred to as "INFORMATION."
For purposes of this Agreement:

                      a. CONFIDENTIAL INFORMATION means INFORMATION disclosed to
or acquired by EMPLOYEE while employed by EMPLOYER, and includes but is not
limited to, INVENTIONS,


<PAGE>   6

Patent Applications, TRADE SECRETS, any other information of value relating to
the business and/or field of interest of EMPLOYER including information with
respect to which EMPLOYER is under an obligation of confidentiality with any
third party. CONFIDENTIAL INFORMATION does not include information that is
generally known in the relevant trade or industry or any information known to
and freely usable by EMPLOYEE before EMPLOYEE'S association with EMPLOYER,
provided, however, information for purposes of this Agreement shall be
considered CONFIDENTIAL INFORMATION if not known by the trade generally, even
though such information has been disclosed to one or more third parties pursuant
to distribution agreements, joint research agreements, or other agreements
entered into by EMPLOYER;

                      b. TRADE SECRET(S) means all information, know-how,
concepts, data, knowledge, ideas and materials however embodied, relating to the
business of EMPLOYER'S customers which have not been released publicly by an
authorized representative of EMPLOYER or have not otherwise lawfully entered the
public domain. TRADE SECRETS shall include but are not limited to information,
know-how, concepts, data, knowledge, computer programs, ideas and materials
relating to EMPLOYER'S existing and future products, processes, research and
development, technology, production costs, contract forms, drawings, designs,
plans, proposals, marketing and sales plans and strategies, cost or pricing
information, financial information, promotional methods, volume of sales, names
or classes of customers and vendors, management procedures, organization charts,
and employee directories.

               17. PROPRIETARY INFORMATION OF OTHERS. EMPLOYEE shall not use or
disclose to EMPLOYER, or induce EMPLOYER to use, any information, know-how,
concepts, data, knowledge, computer programs, ideas or materials, however
embodied, with respect to which EMPLOYEE is under an obligation of
confidentiality to any third party imposed, by law or agreement prior to the
date hereof. EMPLOYER represents and covenants that it will not require EMPLOYEE
to violate any obligation to, or confidence with, another.

               18. SECRECY AGREEMENT. EMPLOYEE acknowledges that he understands
the requirement for CONFIDENTIAL INFORMATION to be kept secret and used only as
authorized herein.


<PAGE>   7

EMPLOYEE shall at all times during the period of his association with EMPLOYER
under this agreement and thereafter keep in confidence and trust all
CONFIDENTIAL INFORMATION. EMPLOYEE shall use CONFIDENTIAL INFORMATION only in
the course of performing duties as Technical Director for Preservation Systems
for the Company and other duties as assigned by the Company President, and not
for unrelated personal gain. EMPLOYEE shall not, directly or indirectly,
disclose any CONFIDENTIAL INFORMATION to any person, organization or entity,
except in the course of performing duties as an EMPLOYEE of EMPLOYER and only in
the manner prescribed by EMPLOYER, or as required by the laws of the U.S. or the
Russian Federation. Employee shall abide by those EMPLOYER policies and
regulations established from time to time for the protection of CONFIDENTIAL
INFORMATION. During EMPLOYEE'S association with EMPLOYER under this Agreement,
and after termination thereof, EMPLOYEE shall not directly, or indirectly,
either as an employee, employer, agent, principal, partner, stockholder,
corporate officer, director, or in any other individual or representative
capacity, engage or participate in any activity of any nature whatsoever, the
performance of which would have a reasonable likelihood of placing EMPLOYEE in
conflict with the obligations of confidence and trust regarding CONFIDENTIAL
INFORMATION imposed herein.

               19. RETURN OF DOCUMENTS AND MATERIALS. EMPLOYEE agrees that all
documents, reports, drawings, materials, designs, plans, computer programs,
proposals, marketing and sales plans, reproductions, and other documents or
things made by EMPLOYEE or that come into EMPLOYEE'S possession in the course of
employment with EMPLOYER are the property of EMPLOYER and will not be used by
EMPLOYEE for any purpose other than the business of EMPLOYER. EMPLOYEE will not
deliver, reproduce or in any way allow such documents or things to be delivered
or be used by any third parties without specific direction or consent of
EMPLOYER. Upon termination of this Agreement, EMPLOYEE will promptly deliver to
EMPLOYER the above documents and materials together with any copies thereof.

               20. NO DISCLOSURE. EMPLOYEE agrees not to divulge, disclose,
convey or make known to others or any other entity, any such information without
the express written consent of the President of HyperBaric Systems first
obtained. EMPLOYEE further agrees to take all necessary steps to safeguard such
information to prevent the unauthorized disclosure thereof.

<PAGE>   8

               21. INJUNCTION. Recognizing that irreparable damage will result
to the business of EMPLOYER in the event of the breach of any of these covenants
and assurances by EMPLOYEE, the parties hereto agree that if EMPLOYEE shall
violate the terms of this Agreement, EMPLOYER shall be entitled to an injunction
to be issued by any court of competent jurisdiction enjoining and restraining
EMPLOYEE and each and every person, firm, association, partnership, company, or
corporation concerned therewith, from the continuance of such violation of the
terms of this Agreement, and in addition thereto, EMPLOYEE shall pay to EMPLOYER
all damages, including reasonable attorneys' fees sustained by EMPLOYER by
reason of the violation of this Agreement.

               22. NO ASSIGNMENT. Neither the EMPLOYEE nor EMPLOYER may transfer
or assign this Agreement, or any right or obligation hereunder, without the
prior written consent of the other party. No right or obligation under this
Agreement may be waived, modified, or in any respect altered except by written
agreement of the parties executed in writing by both parties.

               23. SUCCESSORS AND ASSIGNS. This agreement shall be binding on
the heirs, executors, successors and assigns of the parties.

               24. ATTORNEY'S FEES. If any action is brought to enforce any
obligation created under this Agreement, the Court shall award to the prevailing
party, such reasonable fees, costs, and expenses as may have been incurred by
such party in enforcing its rights under this Agreement, including without
limitation, the fees, costs, and expenses of its attorney for services both
before or after litigation is instituted.

               25. ENTIRE AGREEMENT. This Agreement may not be changed except in
writing signed by the President of the Company and the EMPLOYEE. The validity,
performance, construction, and effect of this Agreement shall be governed by the
laws of the State of California. Any other relationship between the parties not
stipulated by this Agreement shall be regulated by COLL RF and the Laws of the
United States/California if not in conflict with COLL RF. This Agreement is
executed in 2 originals, in English (one for each party). Both originals shall
have equal validity and force.

<PAGE>   9

               IN WITNESS WHEREOF, the parties hereto have executed this
Agreement as of the day and year first above written.

        "EMPLOYER"                           "EMPLOYEE"

HYPERBARIC SYSTEMS.                          VLADIMIR SEREBRENNIKOV
1127 Harker Avenue                           Academgorodok, 1A, Apt 53
Palo Alto, California 94301                  Krasnoyarsk, Russia 660036


By:
   --------------------------------          -----------------------------------

        HARRY MASUDA, PRESIDENT                    VLADIMIR SEREBRENNIKOV