MAXYGEN INC
S-1, 2000-03-03
COMMERCIAL PHYSICAL & BIOLOGICAL RESEARCH
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<PAGE>

     As filed with the Securities and Exchange Commission on March 3, 2000
                                                     Registration No. 333-
- -------------------------------------------------------------------------------
- -------------------------------------------------------------------------------
                      SECURITIES AND EXCHANGE COMMISSION
                             Washington, DC 20549

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

                                   FORM S-1
                            REGISTRATION STATEMENT
                                     UNDER
                          THE SECURITIES ACT OF 1933

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

                                 MAXYGEN, INC.
            (Exact name of Registrant as specified in its charter)

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

<TABLE>
 <S>                                 <C>                                <C>
             Delaware                               8731                            77-0449487
   (State or other jurisdiction         (Primary Standard Industrial             (I.R.S. Employer
 of incorporation or organization)       Classification Code Number)           Identification No.)
</TABLE>

                                 MAXYGEN, INC.
                              515 Galveston Drive
                        Redwood City, California 94063
                                (650) 298-5300
  (Address, including zip code, and telephone number, including area code, of
                 Maxygen, Inc.'s principal executive offices)

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

                           RUSSELL J. HOWARD, Ph.D.
                     President and Chief Executive Officer
                                 MAXYGEN, INC.
                              515 Galveston Drive
                        Redwood City, California 94063
                                (650) 298-5300
(Name, address, including zip code, and telephone number, including area code,
                             of agent for service)

                                  Copies to:

<TABLE>
<S>                                                <C>
                 JULIAN N. STERN                                    BARRY E. TAYLOR
                AUGUST J. MORETTI                                  TREVOR J. CHAPLICK
         Heller Ehrman White & McAuliffe                    Wilson Sonsini Goodrich & Rosati
          2500 Sand Hill Road, Suite 100                        Professional Corporation
        Menlo Park, California 94025-7063                          650 Page Mill Road
            Telephone: (650) 234-4229                         Palo Alto, California 94304
            Facsimile: (650) 234-4299                          Telephone: (650) 493-9300
                                                               Facsimile: (650) 845-5000
</TABLE>

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

  Approximate date of commencement of proposed sale to the public: As soon as
practicable following the effectiveness of this Registration Statement.
  If the only securities being registered on this Form are being offered
pursuant to dividend or interest reinvestment plans, please check the
following box. [_]
  If this Form is filed to register additional securities for an offering
pursuant to Rule 462(b) under the Securities Act of 1933, please check the
following box and list the Securities Act registration number of the earlier
effective registration statement for the same offering: [_]
  If this Form is a post-effective amendment filed pursuant to Rule 462(c)
under the Securities Act of 1933, check the following box and list the
Securities Act registration statement number of the earlier effective
registration statement for the same offering: [_]
  If delivery of the prospectus is expected to be made pursuant to Rule 434,
please check the following box: [_]

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

                        CALCULATION OF REGISTRATION FEE
<TABLE>
- -----------------------------------------------------------------------------------
- -----------------------------------------------------------------------------------
<CAPTION>
                                                          Proposed
                                           Proposed       Maximum
 Title of Each Class of                    Maximum       Aggregate      Amount of
    Securities to be      Amount to be  Offering Price    Offering     Registration
       Registered        Registered(1)   Per Share(2)     Price(2)         Fee
- -----------------------------------------------------------------------------------
<S>                      <C>            <C>            <C>            <C>
Common Stock, $0.0001
 par value............     1,725,000      $160.1875     $276,323,438     $72,950
- -----------------------------------------------------------------------------------
- -----------------------------------------------------------------------------------
</TABLE>
(1) Includes 225,000 shares which the underwriters have the option to purchase
    to cover over-allotments, if any.
(2) Estimated solely for the purpose of computing the amount of the
    registration fee pursuant to Rule 457(c) under the Securities Act of 1933,
    as amended, based on the average of the high and low sale prices of the
    common stock on the Nasdaq National Market on March 1, 2000, as reported
    in The Wall Street Journal.

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

  The Registrant hereby amends this Registration Statement on such date or
dates as may be necessary to delay its effective date until the Registrant
shall file a further amendment which specifically states that this
Registration Statement shall thereafter become effective in accordance with
Section 8(a) of the Securities Act or until the Registration Statement shall
become effective on such date as the Securities and Exchange Commission,
acting pursuant to said Section 8(a), may determine.

- -------------------------------------------------------------------------------
- -------------------------------------------------------------------------------
<PAGE>

                   Subject to Completion, Dated March 3, 2000

                                1,500,000 Shares
                                 [MAXYGEN LOGO]

                                  Common Stock

                                  -----------

  This is an offering of 1,500,000 shares of common stock of Maxygen, Inc.
Maxygen is selling all of the 1,500,000 shares of common stock in this
offering.

  The common stock is quoted on the Nasdaq National Market under the symbol
"MAXY". The last reported sale price of the common stock on March 1, 2000 was
$162.50 per share.

  See "Risk Factors" beginning on page 7 to read about factors you should
consider before buying shares of the common stock.

                                  -----------

  Neither the Securities and Exchange Commission nor any other regulatory body
has approved or disapproved of these securities or passed on the accuracy or
adequacy of this prospectus. Any representation to the contrary is a criminal
offense.

                                  -----------

<TABLE>
<CAPTION>
                                                               Per Share Total
                                                               --------- ------
<S>                                                            <C>       <C>
Initial price to public.......................................   $       $
Underwriting discount.........................................   $       $
Proceeds, before expenses, to Maxygen.........................   $       $
</TABLE>

  To the extent that the underwriters sell more than 1,500,000 shares of common
stock, the underwriters have the option to purchase up to an additional 225,000
shares from Maxygen at the initial price to public less the underwriting
discount.

                                  -----------

  The underwriters expect to deliver the shares against payment in New York,
New York on        , 2000.

Goldman, Sachs & Co.

            Robertson Stephens

                        Credit Suisse First Boston

                                                              Invemed Associates

                                  -----------

                         Prospectus dated      , 2000.
The information in this preliminary prospectus is not complete and may be
changed. These securities may not be sold until the registration statement
filed with the Securities and Exchange Commission is effective. This
preliminary prospectus is not an offer to sell nor does it seek an offer to buy
these securities in any jurisdiction where the offer or sale is not permitted.
<PAGE>


                               PROSPECTUS SUMMARY

   You should read the following summary together with the more detailed
information regarding us, the sale of our common stock in this offering, and
our financial statements and notes to those financial statements that appear
elsewhere in this prospectus.

                                  Our Business

Overview

   We believe that we are the leader in the emerging field of directed
molecular evolution, the process by which genes are modified for specific
commercial uses. Our proprietary directed molecular evolution technologies,
known as MolecularBreeding(TM) technologies, mimic the natural process of
evolution and bring together advances in molecular biology and classical
breeding, while capitalizing on the large amount of genetic information
generated by government, academic and commercial laboratories. Unlike
conventional technologies, MolecularBreeding directed molecular evolution
technologies are efficient, in part because they require minimal understanding
of complex underlying biological systems. We have designed our technologies to
rapidly develop new genes for commercial applications, where such genes would
be difficult or impossible to develop through other processes. We believe our
MolecularBreeding directed molecular evolution technologies are commercially
applicable to a broad range of industries. We are currently conducting research
on more than 40 product candidates for the chemical, agricultural and
pharmaceutical industries, enabling us to potentially generate short-term as
well as long-term revenues.

   We have established collaborations with Novo Nordisk, DuPont/Pioneer Hi-
Bred, AstraZeneca, DSM and Rio Tinto, all leaders in their respective markets,
as well as with United States government agencies. Our commercial collaborators
and U.S. government agencies have committed funding of over $102 million. While
we will continue to establish strategic collaborations with leading companies
and pursue additional grants from U.S. government agencies, we will also invest
our own funds in certain areas. To that end, we have retained significant
product commercialization rights to future applications of our technologies.

Our Target Markets

   Our technologies address a number of multi-billion dollar industries. Our
target markets include chemicals, agriculture, protein pharmaceuticals, and
preventative and therapeutic vaccines. Within these markets, we are focusing
our efforts on specific high-value opportunities. In chemicals, we are
developing new processes using enzymes as catalysts that could increase yields
and decrease manufacturing costs for multiple product classes, such as
vitamins, pharmaceuticals, paints and plastics. In addition, we believe that
processes using enzymes as catalysts may have utility for generating new useful
materials such as fibers for industrial and consumer product applications. In
agriculture, we are applying our technologies to potentially increase crop
yield and qualities, including enhanced nutritional value in human food and
animal feed. In pharmaceuticals and vaccines, we are focusing our efforts on
developing products for a number of indications, including multiple forms of
cancer, infectious diseases such as HIV and hepatitis, and diseases in which
the body generates an improper immune response, such as rheumatoid arthritis
and multiple sclerosis.

Our Technologies

   Our MolecularBreeding directed molecular evolution technologies consist of
two components: DNAShuffling(TM) recombination technologies and MaxyScan(TM)
screening systems. DNAShuffling is the process of recombining single genes or
gene families to generate a library of new modified genes. MaxyScan is a series
of specialized screening systems that efficiently and rapidly select those gene
products and enzymes best suited for specific commercial purposes. We have an
extensive patent

                                       3
<PAGE>

portfolio, including 16 issued U.S. patents, of which six are owned by us and
10 have been licensed to us by others. Furthermore, we have over 55 families of
patent applications relating to our MolecularBreeding directed molecular
evolution technologies, the application of our technologies to diverse
industries and specific proteins improved by our technologies.

Our Accomplishments

   We have attracted a multi-disciplinary team comprised of leading experts in
the field of directed molecular evolution. We have consistently been able to
generate significant enhancements in many different genes that have relevance
to multiple commercial applications. We have demonstrated improvements in 13
product candidates and have an additional 32 product candidates in earlier
stages of development. For example, we have increased the anti-viral activity
of a protein and developed new modified enzymes which have the potential to
streamline chemical and pharmaceutical manufacturing processes. In addition, we
have significantly improved the performance of multiple commercially relevant
properties of the industrial enzyme subtilisin, one of the most studied and
extensively modified commercial enzymes. Subtilisin, which is widely used in
laundry detergents, had annual sales of $500 million in 1998. We believe that
this example demonstrates the ability of our MolecularBreeding directed
molecular evolution technologies to achieve significant improvements beyond the
limits of other approaches in biotechnology.

   To date, we have established strategic alliances with Novo Nordisk in the
area of industrial enzymes, DuPont/Pioneer Hi-Bred and AstraZeneca in
agriculture, DSM in antibiotic manufacturing and Rio Tinto in chemical
processing. Since 1997, our collaborators have committed funding of over $75
million, assuming we perform research for the full term of the existing
collaborations. Of this amount, we have received approximately $33 million,
including $15 million in equity investments. In addition, we could receive over
$145 million in milestone payments based on the accomplishment of specific
performance criteria, as well as royalties on product sales. We have received
six grants from the U.S. National Institute of Standards and Technology-
Advanced Technology Program and the Defense Advanced Research Projects Agency
with total committed grant funding of over $27 million, of which we have
expended approximately $7 million. These grants are primarily for the
development of vaccines and the advancement of our MolecularBreeding directed
molecular evolution technologies.

Our Strategy

   Our strategy has four major components:

   .  We will continue to develop our core MolecularBreeding directed
      molecular evolution technologies to extend our proprietary technology
      leadership by investing significantly in research and development
      programs. We will acquire and license technologies from third parties
      that complement our capabilities.

   .  We will continue to establish strategic collaborations with leading
      companies in targeted industries and will pursue additional grants from
      U.S. government agencies. We have retained, and intend to retain,
      significant rights to develop and market certain applications of
      products arising from our strategic collaborations.

   .  We plan to develop multiple products in the chemicals, agriculture and
      pharmaceutical industries to generate revenues in the short-, medium-
      and long-term. We expect to receive a diversified royalty stream from
      the sale of commercial products and processes that may be developed and
      commercialized by our existing collaborators as well as revenues from
      any products that result from our grant-funded programs and self-funded
      programs.

   .  We plan to retain rights to use our technologies in multiple
      applications. We will invest our own funds in selected areas and product
      opportunities with the aim of capturing a high percentage of profits on
      product sales.

                                       4
<PAGE>


Our History

   We began operations in 1997 to commercialize technologies originally
conceived by Dr. Willem P.C. Stemmer while at Affymax Research Institute, a
subsidiary of Glaxo Wellcome plc. We now have over 145 employees and occupy our
own facilities and executive offices, totaling 47,880 square feet, located at
515 Galveston Drive, Redwood City, California 94063. Our telephone number is
(650) 298-5300. We were incorporated under the laws of Delaware on May 7, 1996.

   Maxygen(TM), MaxyScan(TM), MolecularBreeding(TM), DNAShuffling(TM), and the
Maxygen logo are some of our trademarks. Other service marks, trademarks and
trade names referred to in this prospectus are the property of their respective
owners.

                                  The Offering

<TABLE>
<S>                                            <C>
Shares offered by Maxygen....................  1,500,000 shares
Shares to be outstanding after this
 offering....................................  32,269,644 shares
Nasdaq National Market symbol................  MAXY
Use of proceeds..............................  For research and development activities, for
                                               capital expenditures, to finance possible
                                               acquisitions and investments in technology,
                                               and for working capital and other general
                                               corporate purposes.
</TABLE>

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

   The above information is based on shares outstanding as of February 15,
2000. This information excludes 2,111,602 shares of common stock issuable upon
the exercise of options outstanding as of February 15, 2000 at a weighted
average exercise price of $5.74 per share and 1,943,385 shares of common stock
reserved for future issuance under our benefit plans.



                                       5
<PAGE>

                             Summary Financial Data

    See Note 1 of Notes to Financial Statements for an explanation of the
method used to determine the number of shares used in computing per share data
below. See Note 8 to Financial Statements for information concerning the deemed
dividend upon issuance of convertible preferred stock in August 1999.

<TABLE>
<CAPTION>
                                                   Year Ended December 31,
                                                   --------------------------
                                                    1997     1998      1999
                                                   -------  -------  --------
                                                    (in thousands, except
                                                       per share data)
<S>                                                <C>      <C>      <C>
Statement of Operations Data:
Collaborative research and development revenue.... $   341  $ 1,077  $  8,895
Grant revenue.....................................     --     1,646     5,122
                                                   -------  -------  --------
Total revenues....................................     341    2,723    14,017
Operating expenses:
  Research and development........................   3,074    7,858    19,250
  General and administrative......................   1,461    3,920     7,498
                                                   -------  -------  --------
Total operating expenses..........................   4,535   11,778    26,748
                                                   -------  -------  --------
Loss from operations..............................  (4,194)  (9,055)  (12,731)
Net interest income...............................     161      229     1,413
                                                   -------  -------  --------
Net loss..........................................  (4,033)  (8,826)  (11,318)
Deemed dividend upon issuance of convertible
 preferred stock..................................     --       --     (2,200)
                                                   -------  -------  --------
Net loss attributable to common stockholders...... $(4,033) $(8,826) $(13,518)
Basic and diluted net loss per share.............. $ (0.82) $ (1.31) $  (1.53)
                                                   =======  =======  ========
Shares used in computing basic and diluted net
 loss per share...................................   4,917    6,748     8,854
Pro forma basic and diluted net loss per share....          $ (0.75) $  (0.74)
                                                            =======  ========
Shares used in computing pro forma basic and
 diluted net loss per share.......................           11,762    18,249
</TABLE>

    In the "as adjusted" column below, we have adjusted the actual balance
sheet data to give effect to receipt of the net proceeds from the sale in this
offering of 1,500,000 shares of common stock at an assumed public offering
price of $162.50 per share, after deducting the estimated underwriting
discounts and commissions and estimated offering expenses.

<TABLE>
<CAPTION>
                                                             December 31, 1999
                                                             ------------------
                                                                          As
                                                              Actual   Adjusted
                                                             --------  --------
                                                              (in thousands)
<S>                                                          <C>       <C>
Balance Sheet Data:
Cash and cash equivalents................................... $136,343  $366,187
Working capital.............................................  132,510   362,354
Total assets................................................  145,578   375,422
Non-current portion of equipment financing..................    1,644     1,644
Accumulated deficit.........................................  (24,177)  (24,177)
Total stockholders' equity..................................  133,716   363,560
</TABLE>

                                       6
<PAGE>

                                  RISK FACTORS

    You should carefully consider the risks described below, together with all
of the other information included in this prospectus, before deciding whether
to invest in our common stock. The risks and uncertainties described below are
not the only ones facing Maxygen. Additional risks and uncertainties not
presently known to us or that we currently deem immaterial also may impair our
business operations. The occurrence of any of the following risks could harm
our business, financial condition or results of operations. In such case, the
trading price of our common stock could decline, and you may lose all or part
of your investment.

We Have a History of Net Losses. We Expect to Continue to Incur Net Losses and
We May Not Achieve or Maintain Profitability.

    We have incurred net losses since our inception, including a net loss of
approximately $11.3 million for the year ended December 31, 1999. As of
December 31, 1999, we had an accumulated deficit of approximately $24.2
million. We expect to have increasing net losses and negative cash flow in the
foreseeable future. The size of these net losses will depend, in part, on the
rate of growth, if any, in our contract revenues and on the level of our
expenses. To date, we have derived all of our revenues from collaborations and
grants and will continue to do so in the foreseeable future. Revenues from
collaborations and grants are uncertain because our existing agreements have
fixed terms and because our ability to secure future agreements will depend
upon our ability to address the needs of our potential future collaborators. We
expect to spend significant amounts to fund research and development and
enhance our core technologies. As a result, we expect that our operating
expenses will increase significantly in the near term and, consequently, we
will need to generate significant additional revenues to achieve profitability.
Even if we do achieve profitability, we may not be able to sustain or increase
profitability on a quarterly or annual basis.

We Are an Early Stage Company Deploying Unproven Technologies. If We Do Not
Develop Commercially Successful Products, We May Be Forced to Cease Operations.

    You must evaluate us in light of the uncertainties and complexities
affecting an early stage biotechnology company. Our MolecularBreeding directed
molecular evolution technologies are new and in the early stage of development.
We may not develop products that prove to be safe and efficacious in any
market, meet applicable regulatory standards, are capable of being manufactured
at reasonable costs, or can be marketed successfully.

    We may not be successful in the commercial development of products.
Successful products will require significant development and investment,
including testing, to demonstrate their cost-effectiveness prior to their
commercialization. To date, companies in the biotechnology industry have
developed and commercialized only a limited number of gene-based products. We
have not proven our ability to develop and commercialize products. Further,
none of our potential vaccine or protein therapeutic products are expected to
enter clinical trials within the next year. We must conduct a substantial
amount of additional research and development before any regulatory authority
will approve any of our products. Our research and development may not indicate
that our products are safe and effective, in which case regulatory authorities
may not approve them. Problems frequently encountered in connection with the
development and utilization of new and unproven technologies and the
competitive environment in which we operate might limit our ability to develop
commercially successful products.

                                       7
<PAGE>

Commercialization of Our Technologies Depends On Collaborations With Other
Companies. If We Are Not Able to Find Collaborators in the Future, We May Not
Be Able to Develop Our Technologies or Products.

    Since we do not currently possess the resources necessary to develop and
commercialize potential products that may result from our MolecularBreeding
directed molecular evolution technologies, or the resources to complete any
approval processes which may be required for these products, we must enter into
collaborative arrangements to develop and commercialize products. We have
entered into collaborative agreements with other companies to fund the
development of certain new products for specific purposes. These contracts
expire after a fixed period of time. If they are not renewed or if we do not
enter into new collaborative agreements, our revenues will be reduced and our
products may not be commercialized.

    We have limited or no control over the resources that any collaborator may
devote to our products. Any of our present or future collaborators may not
perform their obligations as expected. These collaborators may breach or
terminate their agreement with us or otherwise fail to conduct their
collaborative activities successfully and in a timely manner. Further, our
collaborators may elect not to develop products arising out of our
collaborative arrangements or devote sufficient resources to the development,
manufacture, market or sale of these products. If any of these events occur, we
may not be able to develop our technologies or commercialize our products.

We Intend to Conduct Proprietary Research Programs, and Any Conflicts With Our
Collaborators or Any Inability to Commercialize Products Resulting from This
Research Could Harm Our Business.

    An important part of our strategy involves conducting proprietary research
programs. We may pursue opportunities in fields that could conflict with those
of our collaborators. Moreover, disagreements with our collaborators could
develop over rights to our intellectual property. Any conflict with our
collaborators could reduce our ability to obtain future collaboration
agreements and negatively impact our relationship with existing collaborators,
which could reduce our revenues.

    Certain of our collaborators could also become competitors in the future.
Our collaborators could develop competing products, preclude us from entering
into collaborations with their competitors, fail to obtain timely regulatory
approvals, terminate their agreements with us prematurely or fail to devote
sufficient resources to the development and commercialization of products. Any
of these developments could harm our product development efforts.

    We will either commercialize products resulting from our proprietary
programs directly or through licensing to other companies. We have no
experience in manufacturing and marketing, and we currently do not have the
resources or capability to manufacture products on a commercial scale. In order
for us to commercialize these products directly, we would need to develop, or
obtain through outsourcing arrangements, the capability to manufacture, market
and sell products. We do not have these capabilities, and we may not be able to
develop or otherwise obtain the requisite manufacturing, marketing and sales
capabilities. If we are unable to successfully commercialize products resulting
from our proprietary research efforts, we will continue to incur losses.

We May Encounter Difficulties in Managing Our Growth. These Difficulties Could
Increase Our Losses.

    We have experienced a period of rapid and substantial growth that has
placed and, if this growth continues, will place a strain on our human and
capital resources. If we are unable to manage this growth effectively, our
losses could increase. The number of our employees increased from 20 to 74 to
143 at December 31, 1997, 1998 and 1999, respectively. Our revenues increased
from $341,000 in 1997 to

                                       8
<PAGE>

$2.7 million in 1998 and $14.0 million in 1999. Our ability to manage our
operations and growth effectively requires us to continue to expend funds to
improve our operational, financial and management controls, reporting systems
and procedures and to attract and retain sufficient numbers of talented
employees. If we are unable to successfully implement improvements to our
management information and control systems in an efficient or timely manner, or
if we encounter deficiencies in existing systems and controls, then management
may receive inadequate information to manage the day-to-day operations of the
Company.

Since Our Technologies Can Be Applied to Many Different Industries, If We Focus
Our Efforts on Industries Which Fail to Produce Viable Product Candidates, We
May Fail to Capitalize on More Profitable Areas.

    We have limited financial and managerial resources. In light of the fact
that our technologies may be applicable to numerous, diverse industries, we
will be required to prioritize our application of resources to discrete
efforts. This requires us to focus on product candidates in selected industries
and forego efforts with regard to other products and industries. Our decisions
may not produce viable commercial products and may divert our resources from
more profitable market opportunities.

Public Perception of Ethical and Social Issues May Limit the Use of Our
Technologies, Which Could Reduce Our Revenues.

    Our success will depend in part upon our ability to develop products
discovered through our MolecularBreeding directed molecular evolution
technologies. Governmental authorities could, for social or other purposes,
limit the use of genetic processes or prohibit the practice of our
MolecularBreeding directed molecular evolution technologies. Ethical and other
concerns about our MolecularBreeding directed molecular evolution technologies,
particularly the use of genes from nature for commercial purposes, and products
resulting therefrom could adversely affect their market acceptance.

If the Public Does Not Accept Genetically Engineered Products, We Will Have
Less Demand for Our Products.

    The commercial success of our potential products will depend in part on
public acceptance of the use of genetically engineered products including
drugs, plants and plant products. Claims that genetically engineered products
are unsafe for consumption or pose a danger to the environment may influence
public attitudes. Our genetically engineered products may not gain public
acceptance. Negative public reaction to genetically modified organisms and
products could result in greater government regulation of genetic research and
resultant products, including stricter labeling laws or regulations, and could
cause a decrease in the demand for our products.

    The subject of genetically modified organisms has received negative
publicity in Europe, which has aroused public debate. The adverse publicity in
Europe could lead to greater regulation and trade restrictions on imports of
genetically altered products. If similar adverse public reaction occurs in the
United States, genetic research and resultant products could be subject to
greater domestic regulation and could cause a decrease in the demand for our
products.

Many Potential Competitors Who Have Greater Resources and Experience Than We Do
May Develop Products and Technologies That Make Ours Obsolete.

    The biotechnology industry is characterized by rapid technological change,
and the area of gene research is a rapidly evolving field. Our future success
will depend on our ability to maintain a competitive position with respect to
technological advances. Rapid technological development by others may result in
our products and technologies becoming obsolete.

                                       9
<PAGE>

    We face, and will continue to face, intense competition from organizations
such as large biotechnology companies, as well as academic and research
institutions and government agencies that are pursuing competing technologies
for modifying DNA. These organizations may develop technologies that are
superior alternatives to our technologies. Further, our competitors in the
directed molecular evolution field may be more effective at implementing their
technologies to develop commercial products. Some of these competitors have
entered into collaborations with leading companies within our target markets to
produce enzymes for commercial purposes.

    Any products that we develop through our MolecularBreeding directed
molecular evolution technologies will compete in multiple, highly competitive
markets. Most of the organizations competing with us in the markets for such
products have greater capital resources, research and development and marketing
staffs and facilities and capabilities, and greater experience in modifying
DNA, obtaining regulatory approvals, manufacturing products and marketing.

    Accordingly, our competitors may be able to develop technologies and
products more easily which would render our technologies and products and those
of our collaborators obsolete and noncompetitive.

Any Inability to Adequately Protect Our Proprietary Technologies Could Harm Our
Competitive Position.

    Our success will depend in part on our ability to obtain patents and
maintain adequate protection of our other intellectual property for our
technologies and products in the U.S. and other countries. If we do not
adequately protect our intellectual property, competitors may be able to
practice our technologies and erode our competitive advantage. The laws of some
foreign countries do not protect proprietary rights to the same extent as the
laws of the U.S., and many companies have encountered significant problems in
protecting their proprietary rights in these foreign countries. These problems
can be caused by, for example, a lack of rules and methods for defending
intellectual property rights.

    The patent positions of biopharmaceutical and biotechnology companies,
including our patent position, are generally uncertain and involve complex
legal and factual questions. We will be able to protect our proprietary rights
from unauthorized use by third parties only to the extent that our proprietary
technologies are covered by valid and enforceable patents or are effectively
maintained as trade secrets. We will apply for patents covering both our
technologies and products as we deem appropriate. However, these applications
may be challenged and may not result in issued patents. Our existing patents
and any future patents we obtain may not be sufficiently broad to prevent
others from practicing our technologies or from developing competing products.
Furthermore, others may independently develop similar or alternative
technologies or design around our patented technologies. In addition, others
may challenge or invalidate our patents, or our patents may fail to provide us
with any competitive advantages.

    We rely upon trade secret protection for our confidential and proprietary
information. We have taken security measures to protect our proprietary
information. These measures may not provide adequate protection for our trade
secrets or other proprietary information. We seek to protect our proprietary
information by entering into confidentiality agreements with employees,
collaborators and consultants. Nevertheless, employees, collaborators or
consultants may still disclose our proprietary information, and we may not be
able to meaningfully protect our trade secrets. In addition, others may
independently develop substantially equivalent proprietary information or
techniques or otherwise gain access to our trade secrets.

Litigation or Other Proceedings or Third Party Claims of Intellectual Property
Infringement Could Require Us to Spend Time and Money and Could Shut Down Some
of Our Operations.

    Our commercial success depends in part on neither infringing patents and
proprietary rights of third parties, nor breaching any licenses that we have
entered into with regard to our technologies and products. Others have filed,
and in the future are likely to file, patent applications covering genes or
gene

                                       10
<PAGE>

fragments which we may wish to utilize with our MolecularBreeding directed
molecular evolution technologies, or products that are similar to products
developed with the use of our MolecularBreeding directed molecular evolution
technologies. If these patent applications result in issued patents and we wish
to use the claimed technology, we would need to obtain a license from the third
party.

    Third parties may assert that we are employing their proprietary technology
without authorization. In addition, third parties may obtain patents in the
future and claim that use of our technologies infringes these patents. We could
incur substantial costs and diversion of management and technical personnel in
defending ourselves against any of these claims or enforcing our patents or
other intellectual property rights against others. Furthermore, parties making
claims against us may be able to obtain injunctive or other equitable relief
which could effectively block our ability to further develop, commercialize and
sell products, and could result in the award of substantial damages against us.
In the event of a successful claim of infringement against us, we may be
required to pay damages and obtain one or more licenses from third parties. We
may not be able to obtain these licenses at a reasonable cost, if at all. In
that event, we could encounter delays in product introductions while we attempt
to develop alternative methods or products. Defense of any lawsuit or failure
to obtain any of these licenses could prevent us from commercializing available
products.

    We routinely monitor the public disclosures of other companies operating in
our industry regarding their technological development efforts. If we determine
that these efforts violate our intellectual property or other rights, we intend
to take appropriate action, which could include litigation. Any action we take
could result in substantial costs and diversion of management and technical
personnel. Furthermore, the outcome of any action we take to protect our rights
may not be resolved in our favor.

If We Lose Our Key Personnel or Are Unable to Attract and Retain Additional
Personnel We May Be Unable to Pursue Collaborations or Develop Our Own
Products.

    We are highly dependent on the principal members of our management and
scientific staff, the loss of whose services might adversely impact the
achievement of our objectives. In addition, recruiting and retaining qualified
scientific personnel to perform future research and development work will be
critical to our success. We do not currently have sufficient executive
management personnel to fully execute our business plan. There is currently a
shortage of skilled executives, which is likely to continue. As a result,
competition for skilled personnel is intense, and the turnover rate can be
high. Although we believe we will be successful in attracting and retaining
qualified personnel, competition for experienced scientists from numerous
companies and academic and other research institutions may limit our ability to
do so on acceptable terms. Failure to attract and retain personnel would
prevent us from pursuing collaborations or developing our products or core
technologies.

    Our planned activities will require additional expertise in specific
industries and areas applicable to the products developed through our
technologies. These activities will require the addition of new personnel,
including management, and the development of additional expertise by existing
management personnel. The inability to acquire these services or to develop
this expertise could impair the growth, if any, of our business.

We Will Need Additional Capital in the Future. If Additional Capital is Not
Available, We Will Have to Curtail or Cease Operations.

    Our future capital requirements will be substantial and will depend on many
factors including payments received under collaborative agreements and
government grants, the progress and scope of our collaborative and independent
research and development projects, the effect of any acquisitions, and the
filing, prosecution and enforcement of patent claims.

                                       11
<PAGE>

    Changes may also occur that would consume available capital resources
significantly sooner than we expect. We may be unable to raise sufficient
additional capital. If we fail to raise sufficient funds, we will have to
curtail or cease operations. We anticipate that the net proceeds of this
offering and interest earned thereon, together with existing cash and cash
equivalents and anticipated cash flows from operations, will enable us to
maintain our currently planned operations for at least the next three years. If
our capital resources are insufficient to meet future capital requirements, we
will have to raise additional funds to continue the development of our
technologies and complete the commercialization of products, if any, resulting
from our technologies.

Some of Our Programs Depend on Government Grants, Which May Be Withdrawn. The
Government Has License Rights to Technology Developed With Its Funds.

    We have received and expect to continue to receive significant funds under
various U.S. government research and technology development programs. The
government may significantly reduce funding in the future for a number of
reasons. For example, some programs are subject to a yearly appropriations
process in Congress. Additionally, we may not receive funds under existing or
future grants because of budgeting constraints of the agency administering the
program. There can be no assurance that we will receive the entire funding
under our existing or future grants.

    Our grants provide the U.S. government a non-exclusive, non-transferable
paid up license to practice for or on behalf of the U.S. inventions made with
federal funds. If the government exercises these rights, the U.S. government
could use these inventions and Maxygen's potential market could be reduced.

Our Potential Therapeutic Products Are Subject to a Lengthy and Uncertain
Regulatory Process. If Our Potential Products Are Not Approved, We Will Not Be
Able to Commercialize Those Products.

    The Food and Drug Administration must approve any vaccine or therapeutic
product before it can be marketed in the U.S. Before we can file a new drug
application or biologic license application with the FDA, the product candidate
must undergo extensive testing, including animal and human clinical trials,
which can take many years and require substantial expenditures. Data obtained
from such testing are susceptible to varying interpretations which could delay,
limit or prevent regulatory approval. In addition, changes in regulatory policy
for product approval during the period of product development and regulatory
agency review of each submitted new application or product license application
may cause delays or rejections. The regulatory process is expensive and time
consuming.

    Because our products involve the application of new technologies and may be
based upon new therapeutic approaches, they may be subject to substantial
review by government regulatory authorities and, government regulatory
authorities may grant regulatory approvals more slowly for our products than
for products using more conventional technologies. We have not submitted an
application with the FDA or any other regulatory authority for any product
candidate, and neither the FDA nor any other regulatory authority has approved
any therapeutic product candidate developed with our MolecularBreeding directed
molecular evolution technologies for commercialization in the U.S. or
elsewhere. We or any of our collaborators may not be able to conduct clinical
testing or obtain the necessary approvals from the FDA or other regulatory
authorities for our products. The regulatory agencies of foreign governments
must also approve our therapeutic products before the products can be sold in
those other countries.

    Even after investing significant time and expenditures, we may not obtain
regulatory approval for our products. Even if we receive regulatory approval,
this approval may entail limitations on the indicated uses for which we can
market a product. Further, once regulatory approval is obtained, a marketed
product and its manufacturer are subject to continual review, and discovery of
previously unknown problems with a product or manufacturer may result in
restrictions on the product, manufacturer and manufacturing facility, including
withdrawal of the product from the market. In certain countries, regulatory
agencies also set or approve prices.

                                       12
<PAGE>

Laws May Limit Our Provision of Genetically Engineered Agricultural Products in
the Future. These Laws Could Reduce Our Ability to Sell These Products.

    We may develop genetically engineered agricultural products. The field
testing, production and marketing of genetically engineered plants and plant
products are subject to federal, state, local and foreign governmental
regulation. Regulatory agencies administering existing or future regulations or
legislation may not allow us to produce and market our genetically engineered
products in a timely manner or under technically or commercially feasible
conditions. In addition, regulatory action or private litigation could result
in expenses, delays or other impediments to our product development programs or
the commercialization of resulting products.

    The FDA currently applies the same regulatory standards to foods developed
through genetic engineering as applied to foods developed through traditional
plant breeding. However, genetically engineered food products will be subject
to premarket review if these products raise safety questions or are deemed to
be food additives. Our products may be subject to lengthy FDA reviews and
unfavorable FDA determinations if they raise questions, are deemed to be food
additives, or if the FDA changes its policy.

    The FDA has also announced in a policy statement that it will not require
that genetically engineered agricultural products be labeled as such, provided
that these products are as safe and have the same nutritional characteristics
as conventionally developed products. The FDA may reconsider or change its
labeling policies, or local or state authorities may enact labeling
requirements. Any such labeling requirements could reduce the demand for our
products.

    The U.S. Department of Agriculture prohibits genetically engineered plants
from being grown and transported except pursuant to an exemption, or under
strict controls. If our future products are not exempted by the USDA, it may be
impossible to sell such products.

Adverse Events in the Field of Gene Therapy May Negatively Impact Regulatory
Approval or Public Perception of Any Gene Therapy Products We or Our
Collaborators May Develop.

    Currently, we are not engaged in developing gene therapy products; however,
we may engage in these activities in the future either for our own account or
with collaborators. If we or our collaborators develop gene therapy products,
these products may encounter substantial delays in development and approval due
to the government regulation and approval process. A recent death and other
adverse events reported in gene therapy clinical trials may lead to more
government scrutiny of proposed clinical trials of gene therapy products,
stricter labeling requirements for these products and delays in the approval of
gene therapy products for commercial sale.

    The commercial success of any potential gene therapy products made by us or
our collaborators will depend in part on public acceptance of the use of gene
therapies for the prevention or treatment of human diseases. Public attitudes
may be influenced by claims that gene therapies are unsafe, and gene therapy
products may not gain the acceptance of the public or the medical community.
Negative public reaction to gene therapy could result in a decrease in demand
for any gene therapy products we or our collaborators may develop.

Health Care Reform and Restrictions on Reimbursements May Limit Our Returns on
Pharmaceutical Products.

    Our future products are expected to include pharmaceutical products. Our
ability and that of our collaborators to commercialize pharmaceutical products
developed with our MolecularBreeding directed molecular evolution technologies
may depend in part on the extent to which reimbursement for the cost of these
products will be available from government health administration authorities,
private health insurers and other organizations. Third-party payors are
increasingly challenging the price of medical products and

                                       13
<PAGE>

services. Significant uncertainty exists as to the reimbursement status of
newly approved health care products, and there can be no assurance that
adequate third party coverage will be available for any product to enable us to
maintain price levels sufficient to realize an appropriate return on our
investment in research and product development.

Our Collaborations With Outside Scientists May Be Subject to Change Which Could
Limit Our Access to Their Expertise.

    We work with scientific advisors and collaborators at academic and other
institutions. These scientists are not our employees and may have other
commitments that would limit their availability to us. Although our scientific
advisors generally agree not to do competing work, if a conflict of interest
between their work for us and their work for another entity arises, we may lose
their services. Although our scientific advisors and collaborators sign
agreements not to disclose our confidential information, it is possible that
certain of our valuable proprietary knowledge may become publicly known through
them.

We May Be Sued for Product Liability.

    We may be held liable if any product we develop, or any product which is
made with the use or incorporation of, any of our technologies, causes injury
or is found otherwise unsuitable during product testing, manufacturing,
marketing or sale. These risks are inherent in the development of chemical,
agricultural and pharmaceutical products. Although we intend to obtain product
liability insurance, this insurance may be prohibitively expensive, or may not
fully cover our potential liabilities. Inability to obtain sufficient insurance
coverage at an acceptable cost or otherwise to protect against potential
product liability claims could prevent or inhibit the commercialization of
products developed by us or our collaborators. If we are sued for any injury
caused by our products, our liability could exceed our total assets.

We Use Hazardous Chemicals and Radioactive and Biological Materials in Our
Business. Any Claims Relating to Improper Handling, Storage or Disposal of
These Materials Could Be Time Consuming and Costly.

    Our research and development processes involve the controlled use of
hazardous materials, including chemicals, radioactive and biological materials.
Some of these materials may be novel, including viruses with novel properties
and animal models for the study of viruses. Our operations also produce
hazardous waste products. Some of our work also involves the development of
novel viruses and viral animal models. We cannot eliminate the risk of
accidental contamination or discharge and any resultant injury from these
materials. Federal, state and local laws and regulations govern the use,
manufacture, storage, handling and disposal of these materials. We believe that
our current operations comply in all material respects with these laws and
regulations. We could be subject to civil damages in the event of an improper
or unauthorized release of, or exposure of individuals to, hazardous materials.
In addition, claimants may sue us for injury or contamination that results from
our use or the use by third parties of these materials, and our liability may
exceed our total assets. Compliance with environmental laws and regulations may
be expensive, and current or future environmental regulations may impair our
research, development, or production efforts. We believe that our current
operations comply in all material respects with applicable Environmental
Protection Agency regulations.

    In addition, certain of our collaborators are working with these types of
hazardous materials in connection with our collaborations. To our knowledge,
the work is performed in accordance with biosafety regulations. In the event of
a lawsuit or investigation, we could be held responsible for any injury caused
to persons or property by exposure to, or release of, these viruses and
hazardous materials. Further, under certain circumstances, we have agreed to
indemnify our collaborators against all damages and other liabilities arising
out of development activities or products produced in connection with these
collaborations.

                                       14
<PAGE>

Management May Invest or Spend the Proceeds of This Offering in Ways With
Which You May Not Agree and in Ways That May Not Yield a Return.

   Management will retain broad discretion over the use of proceeds from this
offering. Stockholders may not deem such uses desirable, and our use of the
proceeds may not yield a significant return or any return at all. Management
intends to use a majority of the proceeds from this offering for research and
development, working capital and other general corporate purposes and to
finance potential acquisitions or investments. Because of the number and
variability of factors that determine our use of the net proceeds from this
offering, we cannot assure you that these uses will not vary substantially
from our currently planned uses. Pending these uses of the net proceeds from
this offering, we intend to invest the net proceeds from this offering in
short-term, interest-bearing, investment grade and U.S. government securities.

Our Stock Price Has Been, and May Continue to Be, Extremely Volatile and You
May Not Be Able to Resell Your Shares at or Above the Offering Price.

   The trading prices of life science company stocks in general, and ours in
particular, have experienced extreme price fluctuations in recent months. The
valuations of many life science companies without consistent product revenues
and earnings, including ours, are extraordinarily high based on conventional
valuation standards such as price to earnings and price to sales ratios. These
trading prices and valuations may not be sustained. Any negative change in the
public's perception of the prospects of biotechnology or life science
companies could depress our stock price regardless of our results of
operations. Other broad market and industry factors may decrease the trading
price of our common stock, regardless of our performance. Market fluctuations,
as well as general political and economic conditions such as recession or
interest rate or currency rate fluctuations, also may decrease the trading
price of our common stock. In addition, our stock price could be subject to
wide fluctuations in response to factors including the following:

  . announcements of new technological innovations or new products by us or
    our competitors;

  . changes in financial estimates by securities analysts;

  . conditions or trends in the biotechnology and life science industries;

  . changes in the market valuations of other biotechnology or life science
    companies;

  . developments in domestic and international governmental policy or
    regulations;

  . announcements by us or our competitors of significant acquisitions,
    strategic partnerships, joint ventures or capital commitments;

  . developments in patent or other proprietary rights;

  . period-to-period fluctuations in our operating results;

  . future royalties from product sales, if any, by our strategic partners;
    and

  . sales of our common stock or other securities in the open market.

   In the past, stockholders have often instituted securities class action
litigation after periods of volatility in the market price of a company's
securities. If a stockholder files a securities class action suit against us,
we would incur substantial legal fees and our management's attention and
resources would be diverted from operating our business in order to respond to
the litigation.

                                      15
<PAGE>

We Expect that Our Quarterly Results of Operations Will Fluctuate, and This
Fluctuation Could Cause Our Stock Price to Decline, Causing Investor Losses.

   Our quarterly operating results have fluctuated in the past and are likely
to do so in the future. These fluctuations could cause our stock price to
fluctuate significantly or decline. Some of the factors which could cause our
operating results to fluctuate include:

  . expiration of research contracts with collaborators or government
    research grants, which may not be renewed or replaced;

  . the success rate of our discovery efforts leading to milestones and
    royalties;

  . the timing and willingness of collaborators to commercialize our products
    which would result in royalties; and

  . general and industry specific economic conditions, which may affect our
    collaborators' research and development expenditures.

   A large portion of our expenses are relatively fixed, including expenses
for facilities, equipment and personnel. Accordingly, if revenues decline or
do not grow as anticipated due to expiration of research contracts or
government research grants, failure to obtain new contracts or other factors,
we may not be able to correspondingly reduce our operating expenses. In
addition, we plan to significantly increase operating expenses in 2000.
Failure to achieve anticipated levels of revenues could therefore
significantly harm our operating results for a particular fiscal period.

   Due to the possibility of fluctuations in our revenues and expenses, we
believe that quarter-to-quarter comparisons of our operating results are not a
good indication of our future performance. Our operating results in some
quarters may not meet the expectations of stock market analysts and investors.
In that case, our stock price would probably decline.

Future Sales of Our Common Stock May Depress Our Stock Price.

   The market price of our common stock could decline as a result of sales of
substantial amounts of our common stock in the public market after the closing
of this offering, or the perception that these sales could occur. In addition,
these factors could make it more difficult for us to raise funds through
future offerings of common stock. There will be approximately 32,269,644
shares of common stock outstanding immediately after this offering, or
approximately 32,494,644 shares if the representatives of the underwriters
exercise their over-allotment option in full. Of these shares, 7,232,134
shares will be freely transferable without restriction or further registration
under the Securities Act, except for any shares held by our "affiliates," as
defined in Rule 144 of the Securities Act, 1,167,866 shares will be subject to
lock-up agreements providing that the stockholders will not offer, sell or
otherwise dispose of any of the shares of common stock owned by them until 90
days after the date of this prospectus and 17,250 shares will be subject to
lock-up agreements which expire on June 13, 2000. The remaining 23,852,394
shares of common stock outstanding will be "restricted securities" as defined
in Rule 144 and may be sold without registration under the Securities Act to
the extent permitted by Rule 144 or other exemptions under the Securities Act.
Our directors, officers and certain stockholders, including greater than 5%
stockholders, who hold approximately 15,711,973 of these remaining shares have
agreed not to sell any of these shares until 90 days after the date of this
prospectus. Other stockholders holding approximately 8,140,421 shares have
agreed in connection with our initial public offering not to sell any of these
shares until June 13, 2000. See "Shares Eligible for Future Sale."

                                      16
<PAGE>

Some of Our Existing Stockholders Can Exert Control Over Us, and May Not Make
Decisions that Are in the Best Interests of All Stockholders.

    After this offering, our officers, directors and principal stockholders
(greater than 5% stockholders) will together control approximately 46% of our
outstanding common stock, and Glaxo Wellcome International B.V. will own
approximately 21% of our outstanding common stock. As a result, these
stockholders, if they act together, and Glaxo Wellcome International B.V. by
itself, will be able to exert a significant degree of influence over our
management and affairs and over matters requiring stockholder approval,
including the election of directors and approval of significant corporate
transactions. In addition, this concentration of ownership may delay or prevent
a change in control of Maxygen and might affect the market price of our common
stock, even when a change may be in the best interests of all stockholders. In
addition, the interests of this concentration of ownership may not always
coincide with our interests or the interests of other stockholders and
accordingly, they could cause us to enter into transactions or agreements which
we would not otherwise consider.

If We Engage in Any Acquisition, We Will Incur a Variety of Costs, and We May
Never Realize the Anticipated Benefits of the Acquisition.

    We are actively evaluating opportunities to acquire businesses,
technologies, services or products that we believe are complementary with our
business activities. If we do undertake any transaction of this sort, the
process of integrating an acquired business, technology, service or product may
result in unforeseen operating difficulties and expenditures and may absorb
significant management attention that would otherwise be available for ongoing
development of our business. Moreover, we may fail to realize the anticipated
benefits of any acquisition. Future acquisitions could reduce your ownership in
Maxygen and could cause us to incur debt, expose us to future liabilities and
result in amortization expenses related to goodwill and other intangible
assets.

    In addition, recent proposed changes in the Financial Accounting Standards
Board rules for merger accounting may affect the cost of making acquisitions or
of being acquired. For example, if these proposed changes become effective we
would likely have to record goodwill or other intangible assets that we would
amortize to earnings if we merge with another company. Such amortization would
adversely impact our future operating results. Further, accounting rule changes
that reduce the availability of write-offs of the value of in-process research
and development in connection with an acquisition could result in the
capitalization and amortization of these amounts which would negatively impact
results of operations in future periods.

Our Facilities Are Located Near Known Earthquake Fault Zones, and the
Occurrence of an Earthquake or Other Catastrophic Disaster Could Cause Damage
to Our Facilities and Equipment, Which Could Require Us to Cease or Curtail
Operations.

    Our facilities are located in the San Francisco Bay Area near known
earthquake fault zones and are vulnerable to damage from earthquakes. In
October 1989 a major earthquake that caused significant property damage and a
number of fatalities struck this area. We are also vulnerable to damage from
other types of disasters, including fire, floods, power loss, communications
failures and similar events. If any disaster were to occur, our ability to
operate our business at our facilities would be seriously, or potentially
completely, impaired. In addition, the unique nature of our research activities
and of much of our equipment could make it difficult for us to recover from a
disaster. The insurance we maintain may not be adequate to cover our losses
resulting from disasters or other business interruptions.

As a New Investor, You Will Experience Immediate and Substantial Dilution.

    If you purchase shares of our common stock in this offering, you will incur
immediate and substantial dilution of $151.27 per share in pro forma net
tangible book value based on an assumed price to the public of $162.50 per
share. If the holders of outstanding options or warrants exercise those options
or warrants, you will incur further dilution. See "Dilution."


                                       17
<PAGE>

                           FORWARD-LOOKING STATEMENTS

    This prospectus contains forward-looking statements within the meaning of
the federal securities laws that relate to future events or our future
financial performance. In some cases, you can identify forward-looking
statements by terminology such as "may," "will," "should," "expect," "plan,"
"anticipate," "believe," "estimate," "predict," "intend," "potential" or
"continue" or the negative of these terms or other comparable terminology.
Examples of these forward-looking statements include, but are not limited to,
statements regarding the following: (1) our MolecularBreeding directed
molecular evolution technologies and processes, (2) our ability to realize
commercially valuable discoveries in our programs, (3) our intellectual
property portfolio, (4) our business strategies and plans and (5) our ability
to develop products suitable for commercialization. These statements are only
predictions.

    Although we believe that the expectations reflected in the forward-looking
statements are reasonable, we cannot guarantee future results, levels of
activity, performance or achievements. Moreover, neither we nor any other
person assumes responsibility for the accuracy and completeness of these
statements. We are under no duty to update any of the forward-looking
statements after the date of this prospectus or to conform these statements to
actual results.

                                USE OF PROCEEDS

    We will receive net proceeds from the sale of the 1,500,000 shares of
common stock of approximately $229,843,750 at an assumed public offering price
of $162.50 per share (approximately $264,395,313 if the underwriters' over-
allotment option is exercised in full), after deducting the estimated
underwriting discounts and offering expenses payable by us.

    We intend to use the net proceeds of the offering for research and
development, working capital and other general corporate purposes and capital
expenditures. The amounts and timing of our actual expenditures will depend
upon numerous factors, including the status of our product development and
commercialization efforts, the amount of proceeds actually raised in this
offering, the amount of cash generated by our operations, competition, and
sales and marketing activities. We are actively evaluating opportunities to
acquire businesses, technologies, services or products that we believe are
complementary with our business activities. We have not determined the amounts
we plan to spend on any of the areas listed above or the timing of these
expenditures. As a result, our management will have broad discretion to
allocate the net proceeds from this offering. Pending application of the net
proceeds as described above, we will invest the net proceeds in short-term,
interest-bearing investment-grade and U.S. government securities.

                                       18
<PAGE>

                          PRICE RANGE OF COMMON STOCK

    Our common stock has been traded on the Nasdaq National Market since our
initial public offering on December 16, 1999 under the symbol "MAXY." Prior to
such time, there was no public market for our common stock. Through March 1,
2000, the high and low sale prices for the common stock, as reported on the
Nasdaq National Market, were as follows:

<TABLE>
<CAPTION>
                                                                  High    Low
                                                                 ------- ------
   <S>                                                           <C>     <C>
   Fourth Quarter 1999 (from December 16, 1999) ................ $ 82.00 $31.98
   First Quarter 2000 (through March 1, 2000)...................  176.00  52.00
</TABLE>

    On March 1, 2000, the last reported closing price of the common stock on
the Nasdaq National Market was $162.50 per share. As of February 15, 2000, we
had outstanding 30,769,644 shares of common stock held by approximately 313
holders of record.

                                DIVIDEND POLICY

    We have never paid cash dividends on our common stock or any other
securities. We anticipate that we will retain all of our future earnings, if
any, for use in the expansion and operation of our business and do not
anticipate paying cash dividends in the foreseeable future.

                                       19
<PAGE>

                                CAPITALIZATION

   The following table sets forth our capitalization as of December 31, 1999:

  . on an actual basis; and

  . on an as adjusted basis to reflect the sale of 1,500,000 shares of common
    stock offered by this prospectus at an assumed public offering price of
    $162.50 per share, after deducting the estimated underwriting discounts
    and offering expenses payable by us.

   The outstanding share information excludes 2,076,362 shares of common stock
issuable upon the exercise of outstanding options under our option plans with
a weighted average exercise price of $4.11 per share as of December 31, 1999.
In addition, the outstanding share information excludes 1,887,488 shares of
common stock reserved for issuance under our stock option and employee stock
purchase plans as of December 31, 1999.

   This information should be read in conjunction with "Management's
Discussion and Analysis of Financial Condition and Results of Operations" and
our financial statements and related notes thereto included elsewhere in this
prospectus.

<TABLE>
<CAPTION>
                                                        December 31, 1999
                                                        ------------------
                                                                     As
                                                         Actual   adjusted
                                                        --------  --------
                                                        (in thousands, except
                                                         share and per share
                                                                data)
<S>                                                     <C>       <C>       <C>
Long-term obligations.................................. $  1,664  $  1,664
                                                        --------  --------
Stockholders' equity:..................................
  Preferred stock, $0.0001 par value; 5,000,000 shares
   authorized; no shares issued and outstanding actual
   and as adjusted.....................................      --        --
  Common stock, $0.0001 par value, 70,000,000 shares
   authorized; 30,860,781 shares issued and
   outstanding, actual; 32,360,781 shares issued and
   outstanding, as adjusted............................        3         3
  Additional paid-in capital...........................  176,517   406,361
  Notes receivable from stockholders...................   (1,411)   (1,411)
  Deferred stock compensation..........................  (17,216)  (17,216)
  Accumulated deficit..................................  (24,177)  (24,177)
                                                        --------  --------
  Total stockholders' equity...........................  133,716   363,560
                                                        --------  --------
Total capitalization................................... $135,380  $365,224
                                                        ========  ========
</TABLE>

                                      20
<PAGE>

                                    DILUTION

    If you invest in our common stock, your interest will be diluted to the
extent of the difference between the public offering price per share of our
common stock and the as adjusted net tangible book value per share of our
common stock after this offering.

    The net tangible book value of Maxygen at December 31, 1999, was $133.7
million, or $4.33 per share of common stock. Net tangible book value per share
represents total tangible assets less total liabilities, divided by the number
of outstanding shares of common stock on December 31, 1999. Our net tangible
book value at December 31, 1999, after giving effect to the sale of the
1,500,000 shares of common stock at an assumed public offering price of $162.50
per share, and after deducting estimated underwriting discounts and commissions
and estimated offering expenses would be $363.6 million or $11.23 per share.
This represents an immediate increase in the net tangible book value of $6.90
per share to existing stockholders and an immediate dilution of $151.27 per
share to new investors, or approximately 93% of the assumed offering price of
$162.50 per share. The following table illustrates this per share dilution:

<TABLE>
<S>                                                                <C>   <C>
Assumed public offering price per share...........................       $162.50
  Net tangible book value per share at December 31, 1999.......... $4.33
  Increase in per share attributable to this offering ............  6.90
                                                                   -----
Net tangible book value per share after this offering ............         11.23
                                                                         -------
Dilution per share to new investors...............................       $151.27
                                                                         =======
</TABLE>

    The following table shows as of December 31, 1999, the number of shares of
common stock purchased from us, the total consideration paid to us and the
average price paid per share by existing stockholders and by new investors
purchasing common stock in this offering at an assumed public offering price of
$162.50 per share, before deducting estimated underwriting discounts and
commissions and estimated offering expenses.

<TABLE>
<CAPTION>
                           Shares Purchased       Total Consideration     Average
                         --------------------- -------------------------   Price
                           Number   Percentage     Amount     Percentage Per Share
                         ---------- ---------- -------------- ---------- ---------
                                               (in thousands)
<S>                      <C>        <C>        <C>            <C>        <C>
Existing stockholders... 30,860,781    95.4%      $159,462       39.5%    $  5.17
New investors...........  1,500,000     4.6        243,750       60.5      162.50
                         ----------   -----       --------      -----
  Total................. 32,360,781   100.0%      $403,212      100.0%
                         ==========   =====       ========      =====
</TABLE>

    The computations in the table above assume no exercise of any stock options
outstanding after December 31, 1999. As of December 31, 1999, there were
options outstanding to purchase a total of 2,076,362 shares of common stock at
a weighted average exercise price of $4.11 per share. If any of these options
are exercised, there will be further dilution to new public investors.

                                       21
<PAGE>

                            SELECTED FINANCIAL DATA

    The statement of operations data for the years ended December 31, 1997,
1998 and 1999 and the balance sheet data as of December 31, 1998 and 1999 are
derived from our financial statements, which have been audited by Ernst & Young
LLP, Independent Auditors, and are included elsewhere in this prospectus. When
you read this selected financial data, it is important that you also read the
historical financial statements and related notes included in this prospectus,
as well as the section of this prospectus entitled "Management's Discussion and
Analysis of Financial Condition and Results of Operations." Historical results
are not necessarily indicative of future results. See Note 1 of Notes to
Financial Statements for an explanation of the method used to determine the
number of shares used in computing pro forma net loss per share. See Note 8 to
Financial Statements for information concerning the deemed dividend upon
issuance of convertible preferred stock in August 1999.

<TABLE>
<CAPTION>
                                                   Year Ended December 31,
                                                   --------------------------
                                                    1997     1998      1999
                                                   -------  -------  --------
                                                    (in thousands, except
                                                       per share data)
<S>                                                <C>      <C>      <C>
Statement Of Operations Data:
Collaborative research and development revenue.... $   341  $ 1,077  $  8,895
Grant revenue.....................................     --     1,646     5,122
                                                   -------  -------  --------
Total revenues....................................     341    2,723    14,017
Operating expenses:
  Research and development........................   3,074    7,858    19,250
  General and administrative......................   1,461    3,920     7,498
                                                   -------  -------  --------
Total operating expenses..........................   4,535   11,778    26,748
                                                   -------  -------  --------
Loss from operations..............................  (4,194)  (9,055)  (12,731)
Net interest income...............................     161      229     1,413
                                                   -------  -------  --------
Net loss..........................................  (4,033)  (8,826)  (11,318)
Deemed dividend upon issuance of convertible
 preferred stock..................................     --       --     (2,200)
                                                   -------  -------  --------
Net loss attributable to common stockholders...... $(4,033) $(8,826) $(13,518)
                                                   =======  =======  ========
Basic and diluted net loss per share.............. $ (0.82) $ (1.31) $  (1.53)
                                                   =======  =======  ========
Shares used in computing basic and diluted net
 loss per share...................................   4,917    6,748     8,854
Pro forma basic and diluted net loss per share
 (unaudited)......................................          $ (0.75) $  (0.74)
                                                            =======  ========
Shares used in computing pro forma basic and
 diluted net loss per share (unaudited)...........           11,762    18,249
</TABLE>

<TABLE>
<CAPTION>
                                                        December 31,
                                                  ---------------------------
                                                   1997      1998      1999
                                                  -------  --------  --------
                                                       (in thousands)
<S>                                               <C>      <C>       <C>
Balance Sheet Data:
Cash and cash equivalents........................  $2,693   $15,306  $136,343
Working capital..................................   2,152    12,264   132,510
Total assets.....................................   3,154    17,600   145,578
Non-current portion of equipment financing
 obligations.....................................      --        --     1,664
Accumulated deficit..............................  (4,033)  (12,859)  (24,177)
Total stockholders' equity.......................   2,571    11,700   133,716
</TABLE>

                                       22
<PAGE>

                    MANAGEMENT'S DISCUSSION AND ANALYSIS OF
                 FINANCIAL CONDITION AND RESULTS OF OPERATIONS

    The following Management's Discussion and Analysis of Financial Condition
and Results of Operations contains forward-looking statements that are based
upon current expectations. These forward-looking statements fall within the
meaning of the federal securities laws that relate to future events or our
future financial performance. In some cases, you can identify forward-looking
statements by terminology such as "may," "will," "should," "expect," "plan,"
"anticipate," "believe," "estimate," "predict," "intend," "potential" or
"continue" or the negative of these terms or other comparable terminology.
Forward-looking statements involve risks and uncertainties. Our actual results
and the timing of events could differ materially from those anticipated in our
forward-looking statements as a result of many factors, including those set
forth under "Risk Factors" and elsewhere in this prospectus.

Overview

    Maxygen was founded in May 1996 and began operations in March 1997. To
date, we have generated revenues from research collaborations with large
agriculture and chemical companies and from government grants. Our current
collaborators are Novo Nordisk, DuPont/Pioneer Hi-Bred, AstraZeneca, DSM and
Rio Tinto. Our government grants are from the Defense Advanced Research
Projects Agency and the National Institute of Standards and Technology-Advanced
Technology Program.

    We have invested heavily in establishing our MolecularBreeding directed
molecular evolution technologies. These investments contributed to revenue
increases from $341,000 in 1997 to $2.7 million in 1998 and $14.0 million in
1999. Our total headcount increased from 20 employees at the end of fiscal 1997
to 74 employees at the end of fiscal 1998 and to 143 employees at the end of
fiscal 1999 of whom 80% were engaged in research and development. Research and
development consisted of work for collaborators, government grant agencies and
work advancing our core technologies.

    We have incurred significant losses since our inception. As of December 31,
1999, our accumulated deficit was $24.2 million and total stockholders' equity
was $133.7 million. Operating expenses increased from $4.5 million in fiscal
1997, to $11.8 million in fiscal 1998 and to $26.7 million in fiscal 1999. We
expect to incur additional operating losses over at least the next several
years as we continue to expand our research and development efforts and
infrastructure.

Source of Revenue and Revenue Recognition Policy

    We recognize revenues from research collaboration agreements as earned upon
achievement of the performance requirements of the agreements. Revenue related
to grant agreements is recognized as related research and development expenses
are incurred. Our existing corporate collaboration agreements with
DuPont/Pioneer Hi-Bred and AstraZeneca provide for research funding for a
specified number of full time researchers working in defined research programs.
Revenue related to these payments is earned as the related research work is
performed. In addition, our collaborators make technology advancement payments
which are intended to fund development of our core technology, as opposed to a
defined research program. These payments are recognized ratably over the
applicable funding period. Payments received that are related to future
performance are deferred and recognized as revenue as the performance
requirements are achieved. As of December 31, 1999, we have deferred revenues
of approximately $7.5 million. Our sources of potential revenue for the next
several years are likely to be research, technology advancement and milestone
payments under existing and possible future collaborative arrangements,
government research grants, and royalties from our collaborators based on
revenues received from any products commercialized under those agreements. See
Note 2 of Notes to Financial Statements.

                                       23
<PAGE>

Deferred Compensation

    Deferred compensation for options granted to employees has been determined
as the difference between the deemed fair market value for financial reporting
purposes of our common stock on the date options were granted and the exercise
price. Deferred compensation for options granted to consultants has been
determined in accordance with Statement of Financial Accounting Standards No.
123 as the fair value of the equity instruments issued. Deferred compensation
for options granted to consultants is periodically remeasured as the underlying
options vest.

    In connection with the grant of stock options to employees, we recorded
deferred stock compensation of approximately $2.6 million, $2.4 million and
$19.5 million in the fiscal years ended December 31, 1997, 1998 and 1999,
respectively. These amounts were initially recorded as a component of
stockholders' equity and are being amortized as charges to operations over the
vesting period of the options using a graded vesting method. We recorded
amortization of deferred compensation of approximately $863,000, $1.6 million
and $4.9 million for the fiscal years ended December 31, 1997, 1998 and 1999,
respectively. The amortization expense relates to options awarded to employees
in all operating expense categories. See Note 8 of Notes to Financial
Statements.

Results of Operations

Comparison of Years Ended December 31, 1998 and 1999

 Revenues

    Our total revenues for fiscal 1998 and 1999 were $2.7 million and $14.0
million, respectively. The increase of $11.3 million was due primarily to the
addition of new research collaborations with AstraZeneca and DuPont/Pioneer Hi-
Bred, new government grants and the expansion of existing government grants.
Collaboration research and development revenue and grant revenue accounted for
40% and 60%, respectively, of total revenues in fiscal 1998, and 63% and 37%,
respectively, of total revenues in fiscal 1999.

 Research and Development Expenses

    Our research and development expenses consist primarily of salaries and
other personnel-related expenses, facility costs, supplies and depreciation of
facilities and laboratory equipment. Research and development expenses
increased 59% from $7.9 million in fiscal 1998 to $19.3 million in fiscal 1999.
The increase was due primarily to increased staffing and other personnel-
related costs to support our additional collaborative and internal research
efforts. Also included in research and development expenses is $783,000 related
to the acquisition of certain technology licenses from research institutions.
The technology is being used in research and development and has no alternative
future uses.

    Research and development expenses represented 289% of total revenues in
fiscal 1998 and 137% of total revenues in fiscal 1999. The decrease as a
percentage of total revenues was due primarily to the growth in our total
revenues. We expect to continue to devote substantial resources to research and
development, and we expect that research and development expenses will continue
to increase in absolute dollars.

 General and Administrative Expenses

    Our general and administrative expenses consist primarily of personnel
costs for finance, human resources, business development, legal and general
management, as well as professional expenses, such as legal and accounting.
General and administrative expenses increased 92% from $3.9 million in fiscal
1998 to $7.5 million in fiscal 1999. Expenses increased primarily due to
increased staffing necessary to manage and support our growth.

                                       24
<PAGE>

    General and administrative expenses represented 144% of total revenues for
fiscal 1998 and 53% of total revenues for fiscal 1999. The decrease as a
percentage of our total revenues was due primarily to the growth in our total
revenues. We expect that our general and administrative expenses will increase
in absolute dollar amounts as we expand our legal and accounting staff, add
infrastructure and incur additional costs related to being a public company,
including directors' and officers' insurance, investor relations programs and
increased professional fees.

 Net Interest Income

    Net interest income represents income earned on our cash and cash
equivalents net of interest expense. Net interest income increased from
$229,000 in fiscal 1998 to $1.4 million in fiscal 1999. This increase was due
to higher average cash balances.

 Deemed Dividend Upon Issuance of Convertible Preferred Stock

    We recorded a deemed dividend of $2.2 million in August 1999 upon the
issuance of Series E convertible preferred stock. At the date of issuance, we
believed the per share price of $6.25 represented the fair value of the
preferred stock and was in excess of the deemed fair value of our common stock.
Subsequent to the commencement of our initial public offering process, we re-
evaluated the deemed fair market value of our common stock as of August 1999
and determined it to be $9.00 per share. Accordingly, the incremental fair
value is deemed to be the equivalent of a preferred stock dividend. We recorded
the deemed dividend at the date of issuance by offsetting charges and credits
to additional paid in capital of $2.2 million, without any effect on total
stockholders' equity. The amount increased the loss allocable to common
stockholders, in the calculation of basic net loss per share for fiscal 1999.

 Provision for Income Taxes

    We incurred net operating losses in fiscal 1998 and 1999, and consequently
we did not pay any federal, state or foreign income taxes. As of December 31,
1999, we had a federal net operating loss carryforwards of approximately
$10.4 million. We also had federal research and development tax credit
carryforwards of approximately $400,000. If not utilized, the net operating
losses and credit carryforwards will expire at various dates beginning in 2011
through 2019. Utilization of the net operating losses and credits may be
subject to a substantial annual limitation due to the change in the ownership
provisions of the Internal Revenue Code of 1986, as amended, and similar state
provisions. The annual limitation may result in the expiration of net operating
losses and credits before utilization. See Note 9 of Notes to Financial
Statements.

Comparison of Years Ended December 31, 1997 and 1998

 Revenues

    Our total revenues for fiscal 1997 and 1998 were $341,000 and $2.7 million,
respectively. The increase of $2.4 million was due primarily to the addition of
new research collaborations and government grants. Collaborative research and
development revenue accounted for 100% of total revenues in fiscal 1997.
Collaborative research and development revenue and grant revenue accounted for
40% and 60%, respectively, of total revenues in fiscal 1998.

 Research and Development Expenses

    Research and development expenses increased from $3.1 million in fiscal
1997 to $7.9 million in fiscal 1998. The increase was due primarily to
increased staffing and other personnel-related costs. Research and development
expenses represented 901% and 289% of total revenues in fiscal 1997 and 1998,
respectively. The decreases as a percentage of total revenues was due primarily
to the growth in our total revenues.

                                       25
<PAGE>

 General and Administrative Expenses

    General and administrative expenses increased from $1.5 million in fiscal
1997 to $3.9 million in fiscal 1998. Expenses increased in each period due
primarily to increased staffing and personnel-related costs resulting from
additional staffing necessary to manage and support our growth. General and
administrative expenses represented 428% of total revenues for fiscal 1997 and
144% of total revenues for fiscal 1998. The decrease as a percentage of our
total revenues was due primarily to the growth in our total revenues.

 Net Interest Income

    Net interest income was $161,000 in fiscal 1997 and $229,000 in fiscal
1998. Changes in interest income were due primarily to changes in our average
cash balances during these periods.

 Provision for Income Taxes

    We incurred net operating losses in fiscal 1997 and 1998 and consequently
we did not pay any federal, state or foreign income taxes.

Liquidity and Capital Resources

    Since inception, we have financed our operations primarily through private
placements and a public offering of equity securities, receiving aggregate
consideration from such sales totaling $157.0 million and research and
development funding from collaborators and government grants totaling $22.0
million. As of December 31, 1999, we had $136.3 million in cash and cash
equivalents and $166,000 available under an equipment financing line of credit.

    Our operating activities used cash of $2.6 million, $2.7 million and $3.0
million in fiscal 1997, 1998 and 1999, respectively. Uses of cash in operating
activities were primarily to fund net operating losses offset by receipt of
funding from collaborators which has been deferred.

    Additions of property and equipment were $459,000, $760,000 and $4.5
million in fiscal 1997, 1998 and 1999, respectively. We expect to continue to
make significant investments in the purchase of property and equipment to
support our expanding operations. We may use a portion of our cash to acquire
or invest in complementary businesses, products or technologies, or to obtain
the right to use such complementary technologies.

    Financing activities provided cash of $5.7 million, $16.1 million and
$128.6 million in fiscal 1997, 1998 and 1999, respectively. These amounts are
the proceeds we received from the sale of preferred stock, net of issuance
costs, and proceeds from the sale of common stock including our initial public
offering in December 1999.

    We expect cash flows from our corporate collaborators for the funding of
research and technology advancement to total approximately $12 million in both
2000 and 2001 and up to this amount in 2002 and 2003 if our collaboration with
DuPont/Pioneer Hi-Bred extends to a fourth and fifth year. DuPont/Pioneer Hi-
Bred may terminate the agreement after three years, upon six months notice if a
specified milestone has not been met. The above amounts include $1 million
annually of technology advancement funding from AstraZeneca. In lieu of making
this payment, AstraZeneca can elect to purchase $3 million of our equity
securities at a 50% premium to the fair value of the securities on the date of
issuance. Cash flows from government grants are determined by the expenses
incurred by the Company. Total remaining committed grant funding amounts to $20
million through fiscal 2002; however some grant programs are subject to a
yearly appropriations process in Congress and we may not receive funds under
existing grants because of budgeting constraints of the agency administering
the program.

                                       26
<PAGE>

    We believe that the net proceeds from this offering and interest earned
thereon, together with our current cash and cash equivalents and funding
received from collaborators and government grants will be sufficient to satisfy
our anticipated cash needs for working capital and capital expenditures for at
least the next three years. However, it is possible that we will seek
additional financing within this timeframe. We may raise additional funds
through public or private financing, collaborative relationships or other
arrangements. We cannot assure you that additional funding, if sought, will be
available on terms favorable to us. Further, any additional equity financing
may be dilutive to stockholders, and debt financing, if available, may involve
restrictive covenants. Our failure to raise capital when needed may harm our
business and operating results.

Disclosure about Market Risk

    Our exposure to market risk is confined to our cash and cash equivalents
which have maturities of less than three months. We maintain an investment
portfolio of depository accounts, master notes and liquidity optimized
investment contracts. The securities in our investment portfolio are not
leveraged, are classified as available-for-sale and are, due to their very
short-term nature, subject to minimal interest rate risk. We currently do not
hedge interest rate exposure. Because of the short-term maturities of our
investments, we do not believe that an increase in market rates would have any
negative impact on the realized value of our investment portfolio.

Impact of Year 2000

    In 1999, we completed our remediation and testing of hardware and software
systems to assess their Year 2000 readiness. We expensed less than $25,000
during 1999 relating to Year 2000 compliance.

    To date, we have not experienced any material adverse effect on our
business or operating results as a result of any Year 2000 problems. In
addition, we have not deferred any material information technology projects or
equipment purchases as a result of our Year 2000 problem activities. However,
we believe that it is not possible to determine with complete certainty that
all Year 2000 problems affecting us have been identified or corrected. If we,
our customers, our providers of hardware and software or our third-party
computer network providers fail to remedy any Year 2000 issues, the reasonably
likely worst case scenario would be the interruption of our research programs,
which could have a material adverse affect on our business, financial
conditions and results of operations. Presently we are unable to quantitatively
estimate the duration and extent of any such interruption, or estimate the
effect such interruption may have on our future revenue. However, we believe
that the impact of any Year 2000 issue on our research operations will be
limited to the ongoing execution of new experiments. We do not expect that any
historical data will be affected.

                                       27
<PAGE>

                                    BUSINESS

Overview

    We believe that we are the leader in the emerging field of directed
molecular evolution, the process by which new, modified genes are generated for
specific commercial uses. Our MolecularBreeding directed molecular evolution
technologies bring together advances in molecular biology and classical
breeding, while capitalizing on the large amount of genetic information being
generated by government, academic and commercial laboratories. Our principal
objective is to maximize the value of our MolecularBreeding directed molecular
evolution technologies through the development of multiple products in a broad
range of industries including agriculture, chemicals and human therapeutics.

    We have established strategic alliances with recognized leaders in our
target industries and with U.S. government agencies. To date, our corporate
collaborators include Novo Nordisk in the area of industrial enzymes,
DuPont/Pioneer Hi-Bred and AstraZeneca in agriculture, DSM in antibiotic
manufacturing and Rio Tinto in chemical processing. Our government grants are
from the Defense Advanced Research Projects Agency (DARPA) and the National
Institute of Standards and Technology-Advanced Technology Program (NIST-ATP)
primarily for the development of vaccines and the advancement of our
MolecularBreeding directed molecular evolution technologies. Committed funding
from our commercial collaborators and grant agencies totals over $102 million.
We may additionally receive over $145 million in milestone payments based on
the accomplishment of specific performance criteria, as well as royalties on
product sales.

    We will continue to establish strategic collaborations with recognized
leaders in several of our target industries and with U.S. government agencies.
We plan to retain significant rights to develop and market products arising
from our funded strategic collaborations. In addition, we will identify and
invest our own funds in certain specific areas and product opportunities with
the aim of capturing a high percentage of profits on product sales. We intend
to fully develop and exploit the breadth of opportunity which we believe can be
addressed by our MolecularBreeding directed molecular evolution technologies.

Background

 Evolution and DNA

    Evolution is the process by which living organisms adapt to their
environment. The first step of this process is sexual reproduction, which
creates a variety of physical characteristics that increase the diversity of a
population. Second, nature exerts a selective force on the individuals,
dictating which characteristics will be favored and be passed to the next
generation. As a result of changing environmental and competitive pressures,
diversity may increase, leading to variation in the physical characteristics of
individuals and species adapted for specific environments.

    The physical characteristics of an organism are determined by genetic
information inherited from the previous generation. This genetic information is
coded for by DNA, a molecule found in the cells of living organisms. DNA is
comprised of four different chemical bases called nucleotides. Human cells have
several billion nucleotides, the precise sequence of which determines the
content of the genetic information. DNA is organized into discrete units called
genes. Genes act alone or in combination to produce proteins, that not only
form the fabric of cells but also direct them to perform biological functions
which may in turn influence physical characteristics. Generally, the inherited
biological properties or physical characteristics of an organism change only
when the DNA in a gene is altered.

    In summary, variations in genes provide the basis for inherited diversity
in a population, thus maximizing the opportunity for developing characteristics
optimally suited for a specific environment.

                                       28
<PAGE>

 Mutation and Recombination

    There are two predominant methods by which nature is able to change the
genetic information encoded by DNA to create diversity: mutation and
recombination.

    All organisms incur a certain number of mutations in their DNA as a result
of normal cellular processes or interactions with external environmental
factors such as radiation from sunlight. Mutation typically involves changes in
individual nucleotides and is essentially random. Almost all mutations are
harmful to the function of genes, but a very small percentage are beneficial
and may pass more broadly into the population.

    Sexually reproducing organisms use recombination, a process that involves
the organized exchange and reassortment of large sections of DNA from their
parents. This process allows for new combinations of genes without disrupting
the function of the newly created genes. This has a significant impact on
physical characteristics and is the primary cause of diversity in a sexually
reproducing population.

Classical Breeding and Its Limitations

    Without any knowledge of the genetic basis of evolution, humans have been
breeding crops and animals for over 4,000 years in the search for better
physical characteristics. All of the domestic breeds of farm animals and
horses, cereal crops, fruits, vegetables, crops for fiber, household pets, most
ornamental flowers and many other species represent the results of many
generations of selective breeding by humans. In all these cases, humans have
cross-bred crops or animals with the most desired physical characteristics to
produce improvements in the next generation. For example, modern corn now has a
dramatically higher yield than the wild strain of corn which produced very
small amounts of grain. This improvement probably began with ancient Inca
farmers continually selecting, breeding and propagating the most robust seed
corn. This is known as classical breeding.

    In the 19th century, advances in biology led to a better understanding of
the basis of heredity. The discovery of the structure of DNA in 1953
subsequently led to the realization that genetic information was responsible
for physical characteristics and that its manipulation could further improve
the breeding process. In modern breeding, the DNA of offspring is often
sequenced to determine whether or not they are carrying undesirable genes. This
reduces the probability of breeding poor quality stock and increases the pace
of improvement.

    Despite the improvements in classical breeding, this technique still has a
number of significant limitations. First, the process is extremely time
consuming, since the offspring must mature in order to determine if they carry
the desired characteristic. For example, this cycle takes several years in
cattle. Second, classical breeding can only be used to breed entire organisms
and cannot readily use genetic information to modify or select for specific
genes and the traits they represent. This limitation is compounded when
multiple genes encode the selected trait or when the simultaneous breeding of
multiple traits is desired. Thus, the scope of potential improvements
accessible by classical breeding is limited.

Modern Biotechnology and Its Current Limitations

    The modern biotechnology industry was founded on the ability to isolate
genes from natural sources, and to make proteins from these genes for use in
production systems. Despite some notable exceptions, the majority of proteins
discovered by scientists and developed by the modern biotechnology industry
have not been commercially successful. Similarly, in the chemical industry,
most naturally occurring enzymes are not efficient or stable enough to be used
for manufacturing chemicals. The lack of product success is due in part to the
fact that the relevant proteins have not been evolved for commercial purposes.

    In recent years, significant research efforts in biotechnology have focused
on identifying genes and elucidating their function. These efforts, which are
known as genomics, have been highly successful in

                                       29
<PAGE>

identifying tens of thousands of genes, but are limited in their ability to
rapidly develop products. This results from two primary causes. First, the
genes identified by genomics have not been evolved for commercial purposes.
Second, once a gene has been identified, a number of steps need to be completed
before the genetic information can be used for the development of products.

    Typical deficiencies of naturally occurring genes and proteins which limit
their commercial utility as therapeutic products include inappropriate
availability in the body, stability, difficulty and cost of manufacture, lack
of specificity, toxicity and other side effects. Similarly, in applications
such as agricultural biotechnology and chemical processes using enzymes as
catalysts, problems include the levels at which proteins can be made,
specificity, stability, efficiency of enzyme function under industrial
manufacturing conditions and purity. In addition, potential products with the
highest commercial value often result from the action of multiple genes or
multiple biological reactions and are difficult to optimize with modern
biotechnology techniques. Many biotechnology companies have abandoned or never
pursued development efforts with potential product candidates as a result of
the unsuitability of the native proteins for commercial uses.

    One approach used by the traditional biotechnology industry to attempt to
improve genes for commercial purposes is random mutagenesis. This technique,
involving the random mutation of genes, usually results in harmful changes. In
addition, the low probability of randomly improving a gene or sequence of
complex biological reactions makes screening for positive changes prohibitively
expensive and time consuming.

    A second approach, rational design, seeks to modify a gene to improve its
properties based on knowledge regarding how the structure of the gene
determines the function of its resultant protein. Fundamental research on the
mechanism of action of the relevant protein is pursued until the knowledge
gained allows a rational prediction of how to change the gene for desired
effect. This process requires many simplifying assumptions, is costly and time
intensive, and has been generally unsuccessful.

    As such, genes and gene products are generally too complex to commercialize
using genomics, rational design, random mutagenesis or other current
technologies.

The Maxygen Solution

    We have developed proprietary MolecularBreeding directed molecular
evolution technologies that address the limitations of classical breeding and
traditional biotechnology by maximizing DNA variation, which is known as
genetic diversity, through directed evolution at the molecular level.
Maximizing genetic diversity increases the opportunity for developing
characteristics optimally suited for a specific commercial purpose. Our
MolecularBreeding directed molecular evolution technologies bring together
advances in molecular biology and classical breeding, while capitalizing on the
wealth of genetic information being developed by genomics. Our technologies are
fast, inexpensive, commercially focused and results oriented. Our approach,
unlike conventional approaches, requires minimal understanding of complex
underlying biological systems.

    There are two components of our MolecularBreeding directed molecular
evolution technologies. The first is DNAShuffling, our proprietary process for
recombining genes into a diverse library of novel DNA sequences known as gene
variants. The second is MaxyScan, a series of proprietary screening
capabilities for the selection of desired commercial properties from the
library of DNA sequences. The combination of DNAShuffling and MaxyScan
specialized screening enables us to identify new products in a rapid,
cost-effective manner.

    Virtually any product or process that utilizes or could utilize DNA or
proteins can potentially be improved for optimal function using our
MolecularBreeding directed molecular evolution technologies. We are therefore
applying our technologies to evolve genes and proteins for use in fields as
diverse as chemicals, agriculture, vaccines and protein pharmaceuticals.

                                       30
<PAGE>

    We believe that our MolecularBreeding directed molecular evolution
technologies provide distinctive advantages over traditional biotechnology, as
summarized in the following table.

     Advantages of Maxygen's MolecularBreeding Directed Molecular Evolution
                                  Technologies


<TABLE>
<CAPTION>
                                                                Maxygen's
                                                            MolecularBreeding
                                                           Directed Molecular
                                                Modern          Evolution
               Characteristic                Biotechnology    Technologies
- ------------------------------------------------------------------------------
  <S>                                        <C>           <C>
  Time to generate lead product candidates   several years   weeks to months
- ------------------------------------------------------------------------------
  Necessary understanding of the biological
   processes underlying lead product
   candidates                                     yes              no
- ------------------------------------------------------------------------------
  Ability to optimally improve properties
   for commercial applications                    no               yes
- ------------------------------------------------------------------------------
  Cost to generate lead product candidates       high              low
- ------------------------------------------------------------------------------
  Amount of resulting genetic diversity         limited    virtually unlimited
</TABLE>


                                       31
<PAGE>

Maxygen's MolecularBreeding Directed Molecular Evolution Technologies

    Our technologies mimic the natural events of evolution. First, genes are
subjected to DNAShuffling, generating a diverse library of gene variants.
Second, our proprietary MaxyScan screening systems select individual proteins
from the gene variants in the library. The proteins that show improvements in
the desired characteristics become the initial lead candidates. After
confirmation of activity, the initial lead candidates are then used as the
genetic starting material for additional rounds of shuffling. Once the level of
improvement needed for the particular commercial application is achieved, the
group of lead candidates is moved forward to the product or process development
stage.

                   [Graphic of MolecularBreeding(TM) Process]

                                       32
<PAGE>

 Step One: DNAShuffling Recombination Technologies

    Our DNAShuffling recombination technologies work as follows: a single gene
or multiple genes are cleaved into fragments and recombined, creating a
population of new gene variants. The new genes created by DNAShuffling are then
selected for one or more desired characteristics. This selection process yields
a population of genes which becomes the starting point for the next cycle of
recombination. As with classical breeding, this process is repeated until genes
expressing the desired properties are identified.

    DNAShuffling recombination technologies can be used to evolve properties
which are coded for by single genes, multiple genes and entire genomes. By
repeating the process, DNAShuffling recombination technologies ultimately
generate libraries with a high percentage of genes which have the desired
function. Due to the high quality of these libraries, a relatively small number
of screening tests need to be performed in order to identify gene variants with
the desired commercial qualities. This process significantly reduces the cost
and time associated with identifying multiple potential products.

 Step Two: MaxyScan Screening

    The ability to screen or select for a desired improvement in function is
essential to the effective development of a newer improved gene or protein. As
a result, we have invested significant resources in developing automated, rapid
screens and selection formats.

    We have developed screening tests which can measure the production of
proteins or small molecules in culture without significant purification steps
or specific test reagents, thereby eliminating time-consuming steps required
for traditional screening tests. We are also focusing on the development of
reliable, cell-based screening tests that are predictive of specific functions
relevant to our human therapeutics programs. Accordingly, we continue to
develop new screening approaches and technologies. Our approach is to create
multitiered screening systems whereby we use a less sensitive screening test as
a first screen to quickly select proteins with the desired characteristics,
followed by a more sensitive screening test to confirm value in these variants
and to select for final lead product candidates. Unlike approaches that create
random diversity, MolecularBreeding produces potentially valuable libraries of
gene variants with a predominance of active genes with the desired function.
This allows us to use complex biological screens and formats as a final
screening test, as relatively few proteins must be screened to detect an
improvement in the starting gene activity.

    We have access to multiple sources of genetic starting material. In
addition to the wealth of publicly available genetic sequence information, we
are able to access our collaborators' proprietary genes. Furthermore, we are
able to inexpensively obtain our own genetic starting material which, when
coupled with the DNAShuffling process, provides a virtually infinite amount of
new, proprietary gene variants with potential commercial value.

    We use certain equipment and vendor software in conjunction with our
DNAShuffling recombination technologies and MaxyScan screening systems, but to
date, have not used internally developed software. We also use other software
purchased from third party vendors to a limited extent in our research and
development activities.

Demonstrated Successes of Our MolecularBreeding Directed Molecular Evolution
Technologies in Multiple Applications

    We have consistently achieved improvement in gene function using our
MolecularBreeding directed molecular evolution technologies. Impressive results
have been demonstrated in many different systems that have relevance to
multiple commercial applications. Our technologies have the ability to generate
improvements that would be difficult, costly, time intensive and, in many
cases, impossible to achieve using other methods. We have shown that we can
achieve improved gene function without a detailed understanding of the
underlying complex biological processes.


                                       33
<PAGE>

    For example, we have demonstrated our ability to improve genes that
increase the anti-viral activity of a protein and develop new enzymes which
have the potential to streamline chemical and pharmaceutical manufacturing
processes. In addition, we have improved the performance of subtilisin, one of
the most commercially valuable laundry detergent enzymes. Subtilisin is one of
the most highly studied enzymes which has been extensively modified to improve
its commercial properties. This example demonstrates the ability of
MolecularBreeding to achieve further improvements beyond the limits of modern
biotechnology. A summary of representative experiments published by our
scientists is set forth below.


<TABLE>
<CAPTION>
        Example                     Property               Activity Increase            Publication
- -----------------------------------------------------------------------------------------------------------
<S>                      <C>                             <C>                    <C>
(Beta)-lactamase         Increased antibiotic            32,000-fold            Nature (1994)
                         resistance/enzyme activity
Antibody                 Increased expression level      100-fold               Nature Medicine (1996)
Antibody                 Increased antibody/receptor     >440-fold              Nature Medicine (1996)
                         binding
Green fluorescent        Increased fluorescence          45-fold                Nature Biotechnology (1996)
 protein
(Beta)-galactosidase     Increase in activity            66-fold activity       Proceedings of the
 to fucosidase                                                                  National Academy of
                                                                                Sciences (1997)
                         Increase in specificity         1,000-fold specificity
Arsenate pathway (3      Increased bacterial resistance  40-fold                Nature Biotechnology (1997)
 genes)                  to arsenate
Cephalosporinase family  Increased antibiotic resistance 270-540-fold           Nature (1998)
Subtilisin protease      Simultaneous improvement        2 to 4 fold in         Nature Biotechnology (1999)
                         in 3 properties                 3 properties
Human (Alpha)-           Increased activity as           285,000-fold           Nature Biotechnology (1999)
 interferon family       measured by antiviral activity
                         on mouse cells
HSV thymidine kinase     Increased sensitivity to        32-fold                Nature Biotechnology (1999)
 family                  prodrug (AZT)
</TABLE>


The Maxygen Strategy

    Our goal is to be the world leader in the commercialization of products and
processes developed using directed molecular evolution. There are four basic
elements to our business strategy:

    Expand Our Proprietary Technology Leadership. In order to expand our
technology leadership, we will continue to develop our core MolecularBreeding
directed molecular evolution technologies by investing significantly in
research and development. We will acquire and license technologies from third
parties that complement our capabilities. We will protect and build on our
existing patent portfolio and also rely on trade secrets to protect our
proprietary technologies. We will continue to recruit and collaborate with
leaders in the field of directed molecular evolution.

    Expand Our Strategic Collaborations and Grants. We will continue to
establish strategic collaborations with leading companies in different
industries. We will also pursue additional grants from major U.S. government
agencies. Our goal is to benefit from the combined expertise of Maxygen and our
collaborators. Additionally, we seek to receive financial support from our
collaborators for research and development of products and for our core
technologies, as well as potential milestone and royalty payments on any
products commercialized.


                                       34
<PAGE>

    Maximize Commercial Applications of Our Technologies. We plan to develop
multiple products for multiple industries. We believe we have short-, medium-
and long-term commercial opportunities in the chemicals, agriculture and
pharmaceutical industries. We believe our technologies have broad commercial
applications, including the development of new and improved pharmaceuticals and
vaccines, better agricultural products and more efficient chemical
manufacturing systems.

    Retain Our Commercialization Rights.  We have invested and plan to invest
our own funds in certain areas and product opportunities with the aim of
capturing a high percentage of profits on product sales.

Potential Fields of Application

    We believe that our MolecularBreeding directed molecular evolution
technologies can be applied to many different industries. We can potentially
improve virtually any product or process that utilizes or could utilize DNA or
proteins using our MolecularBreeding directed molecular evolution technologies.
Potential applications of MolecularBreeding directed molecular evolution
technologies include the development of new high-value products and the
improvement of existing products and manufacturing processes. We can
potentially use multiple approaches to develop products to solve complex
problems, including the following:

 In Medicine

  . New and improved treatments for major diseases such as cancer,
    cardiovascular disease, diabetes and obesity.

  . New vaccines to treat and prevent viral diseases such as hepatitis, AIDS
    and emerging viral diseases and parasitic diseases such as malaria which
    affect millions of people each year.

  . Therapeutic vaccines and gene therapies to treat and prevent diseases
    such as multiple sclerosis, allergies and cancer.

  . New natural products for the development of better and cheaper
    antibiotics to counter the spread of infectious organisms that have
    developed a resistance to conventional antibiotics.

  . New natural products as improved therapies for cancer.

  . New gene therapies for treatments for hereditary diseases such as
    hemophilia and cystic fibrosis.

 In Agriculture and Food Production

  . Crops with increased yields which require less fertilizers, herbicides or
    insecticides.

  . Plants which can thrive on land where they could not otherwise survive,
    for example because of lack of water, high salt level or extreme
    temperatures.

  . Vaccines to treat and prevent diseases of farm animals.

  . Nutritionally improved forms of food and animal feed.

  . Food with increased health benefits.

 In the Chemical Industry

  . New, more cost-effective and more environmentally friendly production
    systems for plastics, vitamins, pharmaceuticals, fibers and adhesives.

  . New materials such as fibers and plastics.

                                       35
<PAGE>

  . Plants as factories for the cheaper and more environmentally friendly
    production of substances such as plastics and pharmaceuticals.

 In the Environmental and Energy Industries

  . New systems for controlling pollution, such as novel processes for
    reduction of carbon emissions and polluting effluents.

  . Preparation of non-polluting and cleaner-burning energy sources.

  . Removal of pollutants, such as sulphur, from oil and other fossil fuels.

Current Fields of Application

    We are currently applying our MolecularBreeding directed molecular
evolution technologies to high-value opportunities in the fields of chemicals,
agriculture, preventative and therapeutic vaccines and protein pharmaceuticals.

 Chemicals

    The chemicals industry is comprised of three major segments: commodity,
specialty and fine chemicals. Together, 1998 sales in these segments exceeded
$800 billion. Within these segments, approximately $50 billion is readily
addressable by biological processing, for example, either by fermentation or
through the use of enzyme catalysts. An additional $200 billion has been
identified as potentially addressable by biological approaches within the next
10-20 years. Included in the potential market is the manufacturing of major
chemicals, plastics, vitamins, compounds used in the manufacture of
pharmaceuticals, enzymes for use as catalysts, the pigments and additives in
paint and the polymers and fibers in our clothing. Enzymes occurring in nature
are generally not able to meet the stringent activity requirements that would
allow for the broad commercial use of enzymes as catalysts.

    We have demonstrated that MolecularBreeding directed molecular evolution
technologies allow for the creation of new modified enzymes for use as
catalysts, and metabolic pathways that overcome the limitations of naturally
occurring enzymes. We are currently generating libraries of proprietary enzymes
for use as catalysts, which we believe will offer a significant competitive
advantage over existing chemical catalysts. These enzymes could provide
increased yields and decreased manufacturing costs by a reduction in
requirements for raw materials, capital equipment and energy. In addition, we
believe these enzyme catalysts will have applicability in generating new useful
materials.

    We have established multiple collaborations in the chemical industry, one
with Novo Nordisk, the world's leading manufacturer of industrial enzymes, one
with DSM, a leader in the production of bulk antibiotic products and
intermediates and one with Rio Tinto, one of the world's largest mining
companies. Our collaboration with Novo Nordisk was established in September
1997. Novo Nordisk had a market share of 45% of the industrial enzymes market
in 1998. The total industrial enzymes market (a segment of the chemicals
market) is estimated at $1.4 billion today, growing to over $3 billion by 2008.
Together with Novo Nordisk, we are applying our MolecularBreeding directed
molecular evolution technologies to the potential production of improved
industrial enzymes. For example, we have significantly improved multiple
commercially relevant properties in subtilisin, one of the most studied and
highly modified industrial enzyme products. Under the five-year agreement, Novo
Nordisk will pay us royalties on any sales of industrial enzyme products that
are developed through our MolecularBreeding directed molecular evolution
technologies.

    In March 1999, we commenced a three-year strategic collaboration with DSM
to evolve new enzymes for use in the manufacture of certain classes of
penicillin antibiotics. We are receiving research funding over the three year
collaboration, and we will receive royalties from the implementation of any
evolved enzymes developed through our MolecularBreeding directed molecular
evolution technologies.

                                       36
<PAGE>

    In January 2000, we entered into a three-year strategic collaboration with
Rio Tinto to develop enzymatic systems for use in carbon dioxide fixation for
use in chemical bioprocessing and other applications. We are receiving research
funding over the three year collaboration, and will share revenues with Rio
Tinto obtained from the use or sale of certain products or processes developed
through our MolecularBreeding directed molecular evolution technologies.

    In addition to the existing collaborations, we expect to pursue independent
development of high-value chemical products, as well as to enter into
additional strategic alliances with leading chemical companies.

 Agriculture

    Today's agricultural biotechnology market is estimated at approximately $1
billion. It is expected to grow to approximately $6 billion by 2005. Over the
past decade, companies have used biotechnology to provide protection from
herbicides, diseases and pests, resulting in impressive increases in crop
yield.

    The need for increased crop yield, the desire to move away from chemical
pesticides, and the determination of the DNA sequence have combined to provide
significant growth in agricultural biotechnology.

    In addition to yield improvement, the agricultural industry is investing
heavily in biotechnology to develop crops with improved qualities such as
higher oil content and enhanced nutritional value for human food or animal
feed.

    A third area of great market potential is the use of plants as "factories"
where the plant produces a substance that has commercial value, generally when
processed and separated from the plant and sold as a pure preparation. Plants
potentially can be used to manufacture pharmaceutical products and specialty or
fine chemicals.

    We believe our MolecularBreeding directed molecular evolution technologies
can be used to create numerous commercial opportunities in crop protection and
plant quality traits. We are developing multiple commercial products for the
agriculture industry through commercial collaborations with two of the world's
leading agriculture companies, AstraZeneca and DuPont/Pioneer Hi-Bred. From
these collaborations we have committed funding of over $61 million and may
receive milestone payments of over $145 million based on the accomplishment of
specific performance criteria, as well as royalties on product sales. The
AstraZeneca and DuPont/Pioneer Hi-Bred collaborations fully fund our research
and development efforts under these collaborations, and provide us with a large
portfolio of potentially high-value gene products for the agricultural markets.

    Together with our collaborators, we are currently working on a broad
portfolio of 12 potential products in areas of yield improvement and quality
traits. We have retained significant rights to develop and market certain
applications of the products resulting from the collaborations. In addition to
the existing collaborations, we are pursuing and expect to pursue independent
development of high-value agricultural products, and intend to enter into
additional strategic alliances with leading agriculture companies.

 Preventative and Therapeutic Vaccines

    Worldwide sales of vaccines in 1998 exceeded $4 billion and are expected to
exceed approximately $10 billion by 2005. Vaccines have been used for decades
to prevent the onset of infectious disease in humans and animals. The vaccine
market has the potential to increase dramatically for the following reasons:

  . Many physicians recognize vaccines as the preferred therapy for numerous
    infectious diseases given the increasing drug resistance of pathogens and
    the inability to prevent or effectively treat traditional and newly
    emerging viral infections.

                                       37
<PAGE>

  . Researchers are investigating vaccines as treatments for cancer,
    autoimmune diseases, allergy and other non-infectious diseases.

  . Adults are increasingly using vaccines.

  . Travelers from developed countries are increasingly using vaccines.

    Vaccines are typically comprised of two elements: antigens, which are
components of the invading pathogen that are recognized by cells of the immune
system and trigger the body's defenses; and adjuvants, which are immune system
boosters. The limited ability of existing antigens and adjuvants to generate
the required immune responses has hindered the development of vaccines. We
believe that we can generate new modified vaccines that have the potential to
overcome the limitations of traditional vaccine development.

    We are building our research and development capabilities in the vaccine
area with the support of government grant funding and have retained full
commercialization rights, subject only to a license to the U.S. government as
required by applicable statutes and regulations. Total committed government
grant funding in the vaccine area is over $22 million.

    We believe our MolecularBreeding directed molecular evolution technologies
have the potential ability to transform the design and development of vaccines
through the identification of new genes and proteins that allow for the
generation of broad and strong immune response. This would enable us to address
both the treatment and prevention of a wide variety of diseases including
cancer, allergy, diseases in which the body generates an improper immune
response and infectious diseases such as AIDS and hepatitis. We are developing
a portfolio of products in the vaccine area, including, for example,
proprietary new improved antigens and adjuvants for stimulating the immune
system.

 Protein Pharmaceuticals

    In 1998, the worldwide sales of therapeutic proteins made using recombinant
DNA technology were approximately $17 billion, and are projected to reach
approximately $19 billion in 2000. Protein pharmaceutical products, such as
erythropoietin (1998 worldwide sales of $4 billion) and granulocyte colony
stimulating factor (1998 worldwide sales of over $1.6 billion) represent some
of the world's highest revenue pharmaceutical products. While some protein
pharmaceuticals containing naturally occurring proteins can address large
markets, many naturally occurring proteins are not well suited for
commercialization without modification. We believe that our MolecularBreeding
directed molecular evolution technologies provide the capabilities necessary to
attain the improvements suitable for commercial use.

    Our MolecularBreeding directed molecular evolution technologies potentially
can be applied to improve existing pharmaceutical proteins, create superior
second generation high-value proteins with, for instance, improved stability,
and create new proteins and pioneer new therapies. Our MolecularBreeding
directed molecular evolution technologies potentially can also be applied to
protein pharmaceuticals to improve desirable biological activities, alter
binding activity, and reduce harmful side effects and toxicities.

    The area of human therapeutics presents significant opportunity for us as
the rapid cloning and sequencing of the human genome is leading to the
identification of hundreds of new genes and proteins that potentially could be
optimized and developed as new protein pharmaceuticals. We are currently
working on a number of protein pharmaceuticals at the research stage. We are
pursuing a two-fold strategy to develop protein pharmaceuticals. First, we
intend to collaborate with leading pharmaceutical and biotechnology companies
and second, we are internally developing our own pharmaceutical product
pipeline for future collaboration opportunities, licensing to others or
independent commercialization.


                                       38
<PAGE>

Areas of Exploration

    In addition to those areas described above, we will continue to evaluate
opportunities in fields such as antibody engineering, food and feed with
enhanced nutritional benefits, natural products, gene therapy, liquid fuels and
environmental applications. We are assessing these and other commercialization
opportunities through discussions with potential corporate and academic
collaborators and U.S. government agencies. In many instances, we have already
established initial technology development and proof of principle models.
Additional development may be funded through federal grants, corporate
collaborators or our own funds.

  Antibodies

    Our MolecularBreeding directed molecular evolution technologies potentially
allow for the generation of new antibodies with improved binding specificity
for their targets and other improved therapeutic properties for multiple
diseases. In particular, monoclonal antibodies, which originate from a single
cell and that have specificity for particular disease targets, are an important
sector of the biotechnology industry representing over 20% of all
biopharmaceutical products in development. The FDA has recently approved for
commercial sale several antibodies, including Genentech's Herceptin(R) and
Novartis' Simulect(R), which have potential utility in a broad range of
diseases.

  Nutritional Compounds

    We believe that our technologies may be applied to individual genes, gene
families and entire complex biological pathways to develop foods, nutritional
supplements and animal feed with improved health benefits. Specific
applications include vitamins, sweeteners, preservatives and cholesterol
lowering agents. These are potentially high-value products that are currently
receiving significant attention in both the food and pharmaceutical industries.

  Natural Product Drug Discovery

    Natural products and natural product derivatives represent approximately
80% of 1998 product sales in the areas of antibiotics and cancer therapies. We
may enter into collaborations with biotechnology and pharmaceutical companies
to generate new libraries of lead natural product compounds by modifying
enzymes and metabolic pathways through MolecularBreeding. We believe that new
enzymes and pathways created through MolecularBreeding may allow for the
generation of natural product variants in ways that are not feasible using
existing chemical synthesis methodologies. Our efforts could potentially create
new natural products with increased activity, stability, availability in the
body or specificity.

  Gene Therapy

    Gene therapy is an approach to treat or prevent certain diseases by
introducing therapeutic genes into target cells to produce specific proteins
that will elicit a desired therapeutic response. We believe that our
MolecularBreeding directed molecular evolution technologies are potentially
well suited to the development of gene delivery and cell-targeting systems that
could improve current modes of disease treatment and prevention. We have
completed two internal programs that demonstrate the technical feasibility of
MolecularBreeding to improve the properties of viral and non-viral gene therapy
delivery methodologies.

  Liquid Fuels and Environmental Uses

    The depletion of fossil fuels and the effects of carbon dioxide emissions
on the environment have raised awareness of the need to develop alternative
fuels. Companies may employ our MolecularBreeding directed molecular evolution
technologies to develop biological systems that produce cleaner burning fuels,
such as methanol and ethanol, from alternative carbon sources, such as plant
biomass and animal waste rather than petroleum. Additionally, companies
potentially could use our MolecularBreeding directed molecular evolution
technologies to develop systems containing enzymes for use as catalysts that
could capture carbon dioxide which would otherwise be released into the
environment, and potentially use the cabon dioxide to produce value-added
products, such as fetilizers, polymers and plastics and cleaner burning fuels.

                                       39
<PAGE>

Corporate Collaborations

    Since inception, we have entered into strategic collaborations and several
additional proof of principle collaborations with commercial entities and have
received six grants from U.S. government agencies. Assuming our research
efforts for existing collaborations are expended for the full research term, we
have total committed funding of over $102 million, of which approximately $75
million is from our collaborators and $27 million from government funding. Of
these committed funds, we have earned approximately $17 million; additionally,
we have received $15 million in consideration of purchase of our equity. In
addition, potential milestone payments from our existing collaborations could
exceed $145 million based on the accomplishment of specific performance
criteria, in addition to earned royalties on product sales. We expect that
strategic collaborations and government grants will continue to be an important
element of our business strategy.

    Our strategy in entering into strategic collaborations is to work with
leaders in their respective industries on specific research projects. Our
agreements grant to our strategic collaborators exclusive licenses under
intellectual property developed by us in the collaboration for specific
products for specific uses. Generally, we retain the right to work ourselves or
with others on projects outside the scope of the areas and projects which are
the subject of our collaborations.

    In the chemicals area, we have entered into research agreements with Novo
Nordisk for industrial enzymes, DSM for enzymes for use in the manufacture of
penicillin and Rio Tinto for chemical process validation. We retain the right
to conduct other projects ourselves or with third parties.

    Even in those areas, such as agriculture, where we have entered into
research agreements with DuPont/Pioneer Hi-Bred and AstraZeneca for multiple
research projects relating to multiple crops and traits, we have the right to
use these same crops to conduct other projects and develop other products, as
well as the right to conduct projects using other crops.

    In our strategic collaborations, in exchange for commercial licenses to the
products developed during the program in specified fields, we typically seek
initial license fees, collaborative research funding, technology advancement
funding, milestone payments for significant developments and royalties on
product sales.

    We have entered into the following significant collaborations:

  Novo Nordisk

    In September 1997, we entered into a five year strategic collaboration with
Novo Nordisk A/S, the world's largest producer of industrial enzymes, for the
development and bulk production of specific industrial enzymes in fields such
as laundry detergents, leather processing and pulp and paper manufacturing.
Industrial enzymes are used for a broad spectrum of activities ranging from
food preparation, to detergents, to pulp and paper manufacturing. Industrial
enzymes today represent over a $1.4 billion market.

    Novo Nordisk will use our MolecularBreeding directed molecular evolution
technologies to generate new industrial enzymes. In addition, Novo Nordisk has
made a five year commitment to contribute funding for the research and
development of new directed evolution technologies. Under the agreement, Novo
Nordisk has an exclusive royalty-bearing license to use our MolecularBreeding
directed molecular evolution technologies to develop proteins and enzymes for
use in certain industrial enzyme fields. We have received an exclusive royalty-
free license to certain Novo Nordisk technologies useful for the practice of
MolecularBreeding in all fields outside the scope of the collaboration, except
the field of human and veterinary diagnostic and therapeutic products, for
which we received a co-exclusive license from Novo Nordisk. Under this
agreement, Novo Nordisk will pay us a royalty on the sales of industrial enzyme
products developed using our MolecularBreeding directed molecular evolution
technologies.

                                       40
<PAGE>

 DuPont/Pioneer Hi-Bred

   In December 1998, we entered into a five year strategic collaboration with
Pioneer Hi-Bred International, Inc., a wholly-owned subsidiary of E.I. duPont
de Nemours and Company, to utilize our MolecularBreeding directed molecular
evolution technologies to generate new gene variants for use in the development
of specific crop protection and quality grain traits in corn, soybeans and
certain other crops. Under the terms of the agreement, in exchange for global
commercialization rights, DuPont/Pioneer Hi-Bred purchased $5 million of our
preferred stock, $5 million of our common stock at our initial public offering
and paid $2.5 million in initial license fees. In addition, DuPont/Pioneer Hi-
Bred has committed to pay us up to $27.5 million over five years for research
and technology development, as well as possible milestone payments of up to
$45 million based on the accomplishment of specific performance criteria and
royalties on future product sales, if any. The agreement may be terminated by
DuPont/Pioneer Hi-Bred after three years, upon six months notice, if a
specified milestone has not been met.

 DSM

   In March 1999, we entered into a three year collaboration with Gist-Brocades
N.V., a subsidiary of DSM N.V., to utilize our proprietary MolecularBreeding
directed molecular evolution technologies to develop certain new enzymes for
use in the manufacture of certain classes of penicillin antibiotics. Under the
terms of the agreement, in exchange for global commercialization rights, we
will receive research funding over three years and will receive royalties from
the commercialization of any enzymes developed through our MolecularBreeding
directed molecular evolution technologies.

 AstraZeneca

   In June 1999, we entered into a five year strategic collaboration with
Zeneca Limited, a wholly-owned subsidiary of AstraZeneca plc, to utilize our
MolecularBreeding directed molecular evolution technologies to improve the
yield and quality of several of AstraZeneca's strategic crops. AstraZeneca is
one of the world's leading agricultural companies. We have received $5 million
in a preferred stock equity investment and could receive up to $21.5 million
for research and development funding and technology advancement funding. We may
receive over $100 million in potential milestone payments based on the
accomplishment of specific performance criteria, in addition to royalties on
product sales. In addition, each year of the collaboration AstraZeneca has the
right to substitute their obligation to pay us $1 million in annual technology
advancement funding with a $3 million equity investment at a 50% premium to the
current market value.

 Rio Tinto

   In January 2000, we entered into a three year collaboration with
Technological Resources Pty Limited, a wholly-owned subsidiary of Rio Tinto
Corporation plc, to utilize our Molecular Breeding directed molecular evolution
technologies to develop enzymatic systems to increase the efficiency of carbon
dioxide fixation for use in chemical bioprocessing and other applications. Rio
Tinto is one of the world's leading mining companies with extensive worldwide
operations in the mining of minerals and metals. In connection with the
collaboration, we will receive research and funding payments and technology
advancement fees from Rio Tinto of up to $2.7 million. Rio Tinto and Maxygen
each have exclusive rights to commercialize technology developed in the
collaboration in specific fields, and Maxygen and Rio Tinto each will share
revenues with the other from certain products or processes that are
commercialized by the other. The collaboration provides that the parties may
create a new entity to commercialize the technology arising from the
collaboration.

   In addition to the above collaborations, we have entered into several proof
of principle collaborations with parties such as Abbott, Pfizer and Novartis.

                                       41
<PAGE>

U.S. Government Grants and Collaborations

    Government grants allow us to focus on key internal scientific programs. In
addition, we retain ownership of all intellectual property and commercial
rights generated during the project, subject to a non-exclusive, non-
transferable, paid-up license to practice for or on behalf of the U.S.
inventions made with federal funds which is retained by the U.S. government as
provided by the applicable statutes and regulations. We have obtained grant
funding of over $27 million, primarily for the development of vaccines and the
advancement of core technology, as outlined below.

                               Summary of Grants


<TABLE>
<CAPTION>
                       Granting                                          Dollar
     Area of Grant      Agency          Description         Grant Date   Amount
- ---------------------------------------------------------------------------------
  <C>                 <C>        <S>                        <C>        <C>
  Improved Drug       NIST-ATP   Use of MolecularBreeding   Sept. 1997 $      2.0
   Testing                       directed molecular                    million
                                 evolution technologies
                                 to develop new screening
                                 systems for use in
                                 accelerated discovery
                                 and development of new
                                 AIDS therapies and
                                 vaccines.

  Evolution of        DARPA      Use of MolecularBreeding    Feb. 1998 $      5.6
   Vectors                       directed molecular                    million
                                 evolution technologies
                                 to evolve a new
                                 generation of DNA
                                 vectors for rapid and
                                 efficient delivery of
                                 antigens for
                                 immunization.

  Whole Genome        NIST-ATP   Use of MolecularBreeding    Oct. 1998 $      1.2
   Shuffling                     directed molecular                    million
                                 evolution technologies
                                 to develop new or
                                 improved manufacturing
                                 processes.

  Decontamination     DARPA      Use of MolecularBreeding    Dec. 1998 $      3.8
                                 directed molecular                    million
                                 evolution technologies
                                 to create enzyme-based
                                 decontamination
                                 compounds effective
                                 against pathogens.

  New Therapeutic and DARPA      Use of MolecularBreeding   April 1999 $      7.7
   Preventative DNA              directed molecular                    million
   Vaccines                      evolution technologies
                                 to generate new vaccines
                                 with a broad spectrum of
                                 activity against
                                 multiple strains of
                                 several different
                                 pathogens.

  Aerosol-Based       DARPA      Use of MolecularBreeding   Sept. 1999 $      6.8
   Vaccines                      directed molecular                    million
                                 evolution technologies
                                 to deliver aerosol-based
                                 preventative and
                                 therapeutic agents.
</TABLE>


    In February 2000, we entered into a cooperative research and development
agreement (CRADA) with the National Cancer Institute, National Institute of
Health. The CRADA is a three year research agreement under which we will work
with the National Cancer Institute to develop with our MolecularBreeding
directed molecular evolution technologies, specific therapeutic proteins for
the treatment of certain types of cancer. We will have the option to acquire an
exclusive, royalty-bearing

                                       42
<PAGE>

license to any inventions owned by the National Cancer Institute that are
developed in the CRADA, on terms to be later established. The CRADA can be
terminated by either the National institute of Health or Maxygen at any time by
advance notice to the other party.

Intellectual Property and Technology Licenses

    Pursuant to the technology transfer agreement we entered into with Affymax
Technologies N.V. and Glaxo Group Limited, each a wholly-owned subsidiary of
Glaxo Wellcome plc, we were assigned all rights to the patents, applications
and know-how related to MolecularBreeding directed molecular evolution
technologies. Affymetrix, Inc. retains an exclusive, royalty-free license under
the patents and patent applications previously owned by Affymax for use in the
diagnostics and research supply markets for specific applications. In addition,
Affymax assigned jointly to us and to Affymetrix a family of patent
applications relating to circular PCR techniques.

    We have an extensive patent portfolio including six issued U.S. patents
relating to our proprietary MolecularBreeding directed molecular evolution
technologies. Counterpart applications of these U.S. patents are pending in
other major industrialized countries. We have an additional 86 pending U.S.
patent applications and 70 pending foreign and international counterpart
applications relating to our MolecularBreeding directed molecular evolution
technologies and specialized screening technologies, and the application of
these technologies to diverse industries including agriculture, protein
pharmaceuticals, vaccines, gene therapy, chemicals and therapeutic drugs.

    We have exclusively licensed patent rights and technology for specific uses
from Novo Nordisk, the California Institute of Technology, Stanford University
and the University of Washington. These licenses give us rights to an issued
U.S. patent, 16 U.S. patent applications, and 81 additional international or
foreign counterpart applications.

    In addition, we received from Affymax a worldwide, non-exclusive license to
certain Affymax patent applications and patents related to technology for
displaying multiple diverse proteins on the surface of bacterial viruses.

Competition

    We believe we are the leader in the field of directed molecular evolution.
We are aware that companies such as Diversa and Ixsys have alternative methods
for obtaining genetic diversity. Academic institutions such as Caltech and the
University of Washington are working in this field, and we have licensed
certain technology from Caltech and the University of Washington. In the
future, we expect the field to become highly competitive and that companies and
academic and research institutions will seek to develop technologies that could
be competitive with our MolecularBreeding directed molecular evolution
technologies.

    Any products that we may develop through our MolecularBreeding directed
molecular evolution technologies will compete in highly competitive markets.
Many of our potential competitors in these markets have substantially greater
financial, technical and personnel resources than we do, and we cannot assure
you that they will not succeed in developing technologies and products that
would render our technologies and products or those of our collaborators
obsolete or noncompetitive. In addition, many of those competitors have
significantly greater experience than we do in their respective fields.

    We are aware that Energy Biosystems Corporation and Diversa Corporation
have described technologies that appear to have some similarities to our
patented proprietary technologies. We monitor publications and patents that
relate to directed molecular evolution to be aware of developments in the field
and evaluate appropriate courses of action in relation to these developments.


                                       43
<PAGE>

Employees

    As of February 15, 2000 we had 149 full-time employees, 64 of whom hold
Ph.D. or M.D. degrees and 119 of whom were engaged in full-time research
activities. We plan to expand our corporate development programs and hire
additional staff as corporate collaborations and government grants are
established. We continue to search for qualified individuals with
interdisciplinary training and flexibility to address the various aspects and
applications of our technologies. None of our employees is represented by a
labor union, and we consider our employee relations to be good.

Facilities

    We lease an aggregate of 47,880 square feet of office and laboratory
facilities in Redwood City, California. The lease expires on February 24, 2005
with respect to 31,166 square feet and on March 31, 2002 with respect to 16,714
square feet. We have an option to extend the term of the lease for three years
with respect to the 16,714 square feet. We believe that the facilities we
currently lease are sufficient for approximately the next three months and that
anticipated future growth for the next six months can be accommodated by
leasing additional space near our current facilities.

Legal Proceedings

    We are not currently a party to any material pending legal proceedings.

                                       44
<PAGE>

                                   MANAGEMENT

Directors and Executive Officers

    Our directors and executive officers as of February 15, 2000, are as
follows:

<TABLE>
<CAPTION>
              Name              Age                  Position
              ----              ---                  --------
 <C>                            <C> <S>
 Russell J. Howard, Ph.D.......  49 Director, President and Chief Executive
                                     Officer
 Simba Gill, Ph.D..............  35 Chief Financial Officer and Senior Vice
                                     President of Business Development
 Michael Rabson, Ph.D..........  46 General Counsel and Senior Vice President
                                     of Legal Affairs
 Willem P.C. Stemmer, Ph.D. ...  42 Vice President of Research
 John Bedbrook, Ph.D...........  50 President of Agriculture
 Howard A. Simon...............  40 Vice President of Human Resources
 Norman Kruse, Ph.D............  50 Director of Intellectual Property, Chief
                                     Patent Counsel
 Isaac Stein (1)(2)............  53 Chairman of the Board and Director
 Robert J. Glaser, M.D. (2)....  81 Director
 M.R.C. Greenwood, Ph.D........  56 Director
 Adrian Hennah (1).............  42 Director
 Gordon Ringold, Ph.D. (1)(2)..  49 Director
 George Poste, D.V.M., Ph.D....  55 Director
 Julian N. Stern...............  75 Secretary
</TABLE>
- --------
(1)Member of the audit and finance committee

(2)Member of the compensation committee

    Russell J. Howard, Ph.D., has served as our President, Chief Executive
Officer and Director since June 1998 and is one of our co-founders. Dr. Howard
was elected our President and Chief Operating Officer in May 1997. Originally
trained in biochemistry and chemistry, Dr. Howard has spent over 20 years
studying infectious diseases, primarily malaria, and currently serves on the
National Institutes of Health and USAID advisory panels for malaria vaccine
development. Prior to joining Maxygen, Dr. Howard was from August 1994 to June
1996 the President and Scientific Director of Affymax Research Institute.

    Simba Gill, Ph.D., joined us in July 1998 as the Chief Financial Officer
and Senior Vice President of Business Development. Prior to joining us, from
November 1996 to July 1998, Dr. Gill was at Megabios Corp. where he was Vice
President of Business Development. Prior to this from November 1995 to November
1996, Dr. Gill was Director of Business Development at Systemix. Prior to
joining Systemix, Dr. Gill worked at Boehringer Mannheim in a variety of
corporate functions including Global Product Manager for erythropoietin,
Manager of Corporate Business Development and Director of New Diagnostics
Program Management. Dr. Gill received his Ph.D. in immunology at King's
College, London University in collaboration with the U.K. biotechnology company
CellTech, and his M.B.A. from INSEAD in Fontainbleau, France.

    Michael Rabson, Ph.D., joined us in September 1999 as Senior Vice President
of Legal Affairs and General Counsel. Prior to joining us from February 1996 to
September 1999, Dr. Rabson was a member of Wilson Sonsini Goodrich & Rosati,
P.C. Prior to becoming a member, Dr. Rabson was an associate at Wilson Sonsini
Goodrich & Rosati, P.C. Dr. Rabson received his Ph.D. in infectious disease
epidemiology from Yale University and did a post-doctoral fellowship at the
National Cancer Institute, National Institutes of Health. He was a patent
examiner at the U.S. Patent and Trademark Office before he received his J.D.
from Yale Law School.

    Willem P.C. Stemmer, Ph.D., is one of our co-founders and the inventor of
MolecularBreeding. He has served as our Vice President of Research since March
1997. Dr. Stemmer's background is in medical genetics, where he originally
worked on antibody engineering for immunotherapy of cancer. Prior to the

                                       45
<PAGE>

organization of Maxygen, he was a distinguished scientist at Affymax Research
Institute from 1992 to 1996. He is a co-founder and board member of the
Diversity Biotechnology Consortium, a joint academic and business effort
focused on theoretical issues in molecular diversity and evolution. Dr. Stemmer
has pioneered our MolecularBreeding directed molecular evolution technologies
and has authored more than 14 papers on the subject and is the named inventor
on more than 20 patent applications covering the technologies and, to date,
five issued patents.

    John Bedbrook, Ph.D., joined us in November 1999 as President of
Agriculture. Prior to this Dr. Bedbrook was Chief Executive Officer of Plant
Science Ventures from the beginning of 1999 until he joined us and Chief
Technology Officer at SAVIA from February 1998 to October 1999. Prior to
joining SAVIA, Dr. Bedbrook held several senior management positions including
Executive Vice President of Research and Development and Co-President at DNA
Plant Technology Corp. from 1988 to 1997. Dr. Bedbrook also served as a
Scientific Board Member and Director for many organizations. Dr. Bedbrook
received his Ph.D. in Molecular Biology from the University of Auckland in New
Zealand.

    Howard A. Simon joined us in November 1999 as Vice President of Human
Resources. Prior to joining us, from 1993 to November 1999 Mr. Simon was a
partner in the Labor, Employment and Benefits Law Group of Landels Ripley &
Diamond, LLP. Mr. Simon is a 1985 graduate of the Boalt Hall School of Law at
the University of California, Berkeley. Also in 1985, Mr. Simon received his
Master of Arts Degree with highest honors from the Graduate Theological Union
of Berkeley.

    Norman Kruse, Ph.D., joined us in March 1998 as the Director of
Intellectual Property, Chief Patent Counsel. Prior to joining us, from December
1995 to February 1998, Dr. Kruse was a patent attorney at Chiron Corporation.
Dr. Kruse was a patent attorney at Townsend and Townsend and Crew from January
1993 to December 1995. Dr. Kruse received his Ph.D. in molecular biology from
the University of Washington and worked initially as a scientist and manager in
the diagnostics industry. Subsequently, he managed technology assessment and
acquisition for Triton Biosciences, during which time he obtained his J.D. from
Golden Gate University of Law in San Francisco.

    Isaac Stein has served as our Chairman of the Board since June 1998 and a
director since May 1996 and is one of our co-founders. Since November 1982, Mr.
Stein has been president of Waverley Associates, Inc. a private investment
firm. Mr. Stein is also a Managing Member of Technogen Enterprises, L.L.C. and
Technogen Managers, L.L.C., which is the general partner of Technogen
Associates, L.P. and a director of ALZA Corporation, the Benham Group of mutual
funds and CV Therapeutics, Inc. He is also a trustee of Stanford University and
the Chairman of the Board of UCSF Stanford Health Care.

    Robert J. Glaser, M.D., has served as our Director since September 1997.
Dr. Glaser was Director for Medical Science at the Lucille P. Markey Charitable
Trust from 1984 to June 1997, and a trustee from 1988 to June 1997. In
accordance with the donor's will, the Trust ceased operations in June 1997. Dr.
Glaser is also a director of ALZA Corporation and Hanger Orthopedic Group, Inc.
Dr. Glaser has held faculty appointments at several universities, including
Dean of the School of Medicine at Stanford University and Professor of Social
Medicine at Harvard University. Originally trained as an internist, Dr. Glaser
has 124 publications on streptococcal infections, rheumatic fever, medical
education and health care, as well as being a contributor to numerous
scientific treatises.

    M.R.C. Greenwood, Ph.D., has served as our Director since February 1999.
Dr. Greenwood has been Chancellor of the University of California ("UC") at
Santa Cruz since July 1996. Prior to being named Chancellor of UC Santa Cruz,
Dr. Greenwood was Dean of Graduate Studies and Vice President at UC Davis from
July 1989 to July 1996. In addition, from November 1993 to May 1995, Dr.
Greenwood took a leave from UC Davis to serve as Associate Director for Science
in the White House Office of Science and Technology Policy. Dr. Greenwood
received her doctorate in physiology, developmental biology and neurosciences
from Rockefeller University.


                                       46
<PAGE>

   Adrian Hennah has served as our Director since September 1997. Mr. Hennah
has held several key positions in the Glaxo Wellcome organization. He is
currently leading a coordination team planning for the integration of Glaxo
Wellcome with Smithkline Beecham. He was previously Senior Vice President and
Chief Financial Officer of Glaxo Wellcome Inc. Prior to that, Mr. Hennah had a
range of responsibilities within research and development including finance,
business redesign and strategy process, human resources and engineering at
Glaxo Wellcome plc since 1984, and he led the team coordinating the
integration of Glaxo and Wellcome. Mr. Hennah is also a Director of
Affymetrix. Mr. Hennah has a degree in law from Cambridge University and is a
Sloan Fellow of the London Business School.

   Gordon Ringold, Ph.D., has served as our Director since September 1997. Dr.
Ringold has served as Chairman and Chief Executive Officer of SurroMed, a
biotechnology company focused on novel clinical databases since 1997. From
March 1995 to February 2000, Dr. Ringold was Chief Executive Officer and
Scientific Director of Affymax Research Institute where he managed the
development of novel technologies to accelerate the pace of drug discovery.
Prior to serving as Chief Executive Officer, Dr. Ringold was the President and
Scientific Director of Affymax Research Institute. Dr. Ringold received his
Ph.D. in the laboratory of Dr. Harold Varmus, prior to joining the Stanford
University School of Medicine, Department of Pharmacology, and serving as the
Vice President and Director of the Institute for Cancer and Development
Biology of Syntex Research. Dr. Ringold is a Managing Member of Technogen
Enterprises, L.L.C. and Technogen Managers, L.L.C., which is the general
partner of Technogen Associates, L.P.

   George Poste, D.V.M., Ph.D., has served as our Director since October 1999.
Dr. Poste has been Chief Science and Technology Officer at SmithKline Beecham
since January 1997 and is a member of the Board of Directors of SmithKline
Beecham. Prior to being appointed to Chief Science and Technology Officer, Dr.
Poste was President of Research and Development at SmithKline Beecham since
1989. Dr. Poste is also a Research Professor at the University of Pennsylvania
and holds the William Pitt Fellowship at Pembroke College, Cambridge
University. He is a Board-certified pathologist and was awarded a D.Sc. for
meritorious research contributions by the University of Bristol in 1987. Dr.
Poste received his Doctorate in Veterinary Medicine in 1966 and his Ph.D. in
Virology in 1969 from the University of Bristol.

   Julian N. Stern has served as our Secretary since March 1997. He has been
an attorney with the law firm of Heller Ehrman White & McAuliffe since 1956.
He is currently the sole employee of a professional corporation that is a
partner of Heller Ehrman. He is also a director of ALZA Corporation.

Scientific Advisory Board

   The following individuals are members of our Scientific Advisory Board:

   Baruch S. Blumberg, M.D., Ph.D., is a Distinguished Scientist at Fox Chase
Cancer Center, Philadelphia, and University Professor of Medicine and
Anthropology at the University of Pennsylvania. Dr. Blumberg's research has
covered many areas including clinical research, epidemiology, virology,
genetics and anthropology. Dr. Blumberg was awarded the Nobel Prize in 1976
for his work on infectious diseases and specifically for the discovery of the
hepatitis B virus and has also been elected to the National Inventors Hall of
Fame for similar work. Dr. Blumberg's research and insight into infectious
diseases are valuable to Maxygen programs related to vaccines and hepatitis B
in particular.

   Arthur Kornberg, M.D., is an active Professor Emeritus at the Stanford
University School of Medicine, Department of Biochemistry. Dr. Kornberg has
received numerous accolades including several honorary degrees and awards, the
National Medal of Science, and the Nobel Prize in Medicine in 1959. He is a
member of several prestigious scientific societies and serves as a member of
several scientific advisory boards. Dr. Kornberg's years of research in
enzymes and metabolism is a valuable contribution to directing the internal
research programs of Maxygen.


                                      47
<PAGE>

    Joshua Lederberg, Ph.D., a research geneticist, is Professor Emeritus at
the Rockefeller University, in New York. Formerly, Dr. Lederberg was a
professor of genetics at the University of Wisconsin and at Stanford University
School of Medicine. Dr. Lederberg is a pioneer in the field of bacterial
genetics with the discovery of genetic recombination in bacteria, work for
which he received the Nobel Prize in Physiology and Medicine in 1958. Maxygen
is funding work in Dr. Lederberg's laboratory pertaining to the study of cell
fusion and the generation of genetically diverse recombinants. His work and
guidance in genetic recombination is important to our MolecularBreeding
directed molecular evolution technologies.

    Alejandro C. Zaffaroni, Ph.D., is one of our co-founders. Dr. Zaffaroni is
a biochemist by training and a highly successful biotechnology entrepreneur,
who has co-founded and built several companies including ALZA Corporation, DNAX
Institute of Molecular and Cellular Biology, Affymax N.V. and Affymetrix, Inc.
Dr. Zaffaroni has repeatedly recognized the commercial value of leading-edge
technologies and has turned those visions into highly successful companies. In
1995, Dr. Zaffaroni was awarded the National Medal of Technology by President
Clinton in recognition of his contributions to the pharmaceutical and
biotechnology industries. Dr. Zaffaroni is a Managing Member of Technogen
Enterprises, L.L.C. and Technogen Managers, L.L.C., which is the general
partner of Technogen Associates, L.P.

    Frances Arnold, Ph.D., is a Professor of Chemical Engineering and
Biochemistry at the California Institute of Technology. She received her Ph.D.
in Chemical Engineering from the University of California, Berkeley. She has
authored or co-authored more than 120 publications and has 18 patents issued or
pending. Dr. Arnold's research focuses on engineering new enzymes and pathways
by directing their evolution in the laboratory. Her awards include an Office of
Naval Research Young Investigator Award, a Presidential Young Investigator
Award and a David and Lucille Packard Fellowship in Science and Engineering.
Maxygen is funding work at Dr. Arnold's laboratory pertaining to directed
molecular evolution. Dr. Arnold provides on-going guidance in the field of
directed molecular evolution and its applications in the chemical industry.

Board Composition and Committees

    We currently have seven directors who each serve until the next meeting of
stockholders and until their successors are duly qualified.

    Our board of directors currently has an audit committee and a compensation
committee. The audit committee consists of Adrian Hennah, Gordon Ringold and
Isaac Stein. The audit committee makes recommendations to the board of
directors regarding the selection of independent auditors, reviews the scope of
audit and other services by our independent auditors, reviews the accounting
principles and auditing practices and procedures to be used for our financial
statements and reviews the results of those audits. The compensation committee
consists of Robert J. Glaser, Gordon Ringold and Issac Stein. The compensation
committee makes recommendations to the board of directors regarding our stock
and compensation plans, approves compensation of certain officers and grants
stock options.

Compensation Committee Interlocks and Insider Participation Interlocks

    None of the members of the compensation committee is currently, or has ever
been at any time since our formation, one of our officers or employees, nor has
served as a member of the board of directors or compensation committee of any
entity that has one or more officers serving as a member of our board of
directors or compensation committee.

    In March 1997, Mr. Stein issued a full recourse promissory note in the
amount of $120,000 in favor of Maxygen in connection with the purchase of
600,000 shares of our common stock, which he repaid in full in January 2000.

                                       48
<PAGE>

Director Compensation

    We reimburse our nonemployee directors for expenses incurred in connection
with attending board and committee meetings but do not compensate them for
their services as board or committee members. We have in the past granted
nonemployee directors options to purchase our common stock pursuant to the
terms of our stock plans, and our board continues to have the discretion to
grant options to new nonemployee directors. Beginning after our stockholders
meeting in 2000, our nonemployee directors will each receive nondiscretionary,
automatic grants of options to purchase 20,000 shares of our common stock upon
joining the board of directors and nondiscretionary, automatic grants of
options to purchase 5,000 shares of our common stock each year pursuant to the
1999 Nonemployee Directors Stock Option Plan.

Executive Compensation

    The following table sets forth the compensation paid by us during 1997,
1998 and 1999 to our Chief Executive Officer and to our four other most highly
compensated executive officers.

                           Summary Compensation Table

<TABLE>
<CAPTION>
                                                                   Long-Term
                                       Annual Compensation        Compensation
                                  -----------------------------   ------------
                                                                     Awards
                                                                  ------------
                                                                   Number of
                                                                   Securities
                                                   Other Annual    Underlying     All Other
     Name and Position       Year  Salary   Bonus  Compensation     Options    Compensation(1)
     -----------------       ----  ------   -----  ------------   ------------ ---------------
<S>                          <C>  <C>      <C>     <C>            <C>          <C>
Russell J. Howard........... 1999 $225,000 $   --    $   --          172,500        $832
 President, Chief Executive  1998  218,333     --        --          200,000         833
 Officer and Director        1997  153,750     --        --          150,000         666
Simba Gill(2)............... 1999  192,850     --      1,500(3)      126,738         686
 Chief Financial Officer and 1998   99,750  10,000    55,414(4)      330,000         275
 Senior Vice President of    1997      --      --        --              --          --
 Business Development
Michael Rabson(5)........... 1999   57,539     --        --          350,000         145
 Senior Vice President of    1998      --      --        --              --          --
 Legal Affairs and           1997      --      --        --              --          --
 General Counsel
Willem P.C. Stemmer......... 1999  154,500     --        --          122,500         786
 Vice President of Research  1998  136,667     --        --              --          502
                             1997   81,667     --        --          300,000         345
John Bedbrook(6)............ 1999   34,599     --        --          200,000         310
 President of Agriculture    1998      --      --        --              --          --
                             1997      --      --        --              --          --
Norman Kruse................ 1999  147,791     --     32,209(7)       66,543
 Director of Intellectual    1998  118,767  10,000   114,809(8)       87,500
 Property, Chief Patent      1997      --      --
 Counsel
Joseph Affholter(10)........ 1999  139,019     --     62,321(9)       65,700         541
 Former Vice President of    1998   84,480  10,000    85,264(10)     110,000         393
 Biocatalysis and Chemicals  1997      --      --        --              --          --
</TABLE>
- --------
 (1) Consists of term life insurance premiums paid by Maxygen on behalf of the
     listed individual.

 (2) Dr. Gill joined Maxygen in July 1998. His annualized salary for 1998 was
     $190,000.

 (3) Consists of $1,500 for reimbursement of relocation expenses.

 (4) Consists of $19,550 in the form of a housing allowance and $35,864 for
     reimbursement of relocation expenses.

 (5) Dr. Rabson joined Maxygen in September 1999. Dr. Rabson's annualized
     salary for 1999 was $220,000.

 (6) Dr. Bedbrook joined Maxygen in November 1999. Dr. Bedbrook's annualized
     salary for 1999 was $212,500.

 (7) Consists of $32,209 in the form of a housing allowance.

 (8) Consists of $31,233 in the form of a housing allowance and $83,575 for
     reimbursement of relocation expenses.

                                       49
<PAGE>

 (9) Consists of $55,381 in the form of a housing allowance and $6,946 as
     interest forgiven on a promissory note.

(10) Consists of $39,953 in the form of a housing allowance, $42,444 for
     reimbursement of relocation expenses and $2,867 as interest forgiven on a
     promissory note.

(11) Dr. Affholter joined Maxygen in May 1998. In January 2000, Dr. Affholter
     resigned as our Vice President of Biocatalysis and Chemicals and is no
     longer an employee.

        Stock Options Granted in the Fiscal Year Ended December 31, 1999

    The following table sets forth information with respect to stock options
granted during the fiscal year ended December 31, 1999 to each of the named
executive officers. All options were granted under Maxygen's 1997 Stock Option
Plan. The following options are immediately exercisable in full at the date of
grant, but shares purchased on exercise of unvested options are subject to a
repurchase right in our favor that entitles us to repurchase unvested shares at
their original exercise price on termination of the employee's services with
us. The repurchase right lapses as to 25% of the shares on the first
anniversary of the grant date and the balance, ratably by year, over the next
three years. Under certain circumstances the vesting of options, and
consequently the lapse of the repurchase right, may be accelerated. See "--
Employee Benefit Plans--1997 Stock Option Plan".

    The percentage of options granted is based on an aggregate of 2,986,830
options granted by Maxygen during the fiscal year ended December 31, 1999 to
our employees, including the named executive officers. The potential realizable
value amounts in the last two columns of the following chart represent
hypothetical gains that could be achieved for the respective options if
exercised at the end of the option term assuming an initial price equal to
$16.00, the initial public offering price. The assumed 5% and 10% annual rates
of stock price appreciation from the date of grant to the end of the option
term are provided in accordance with rules of the SEC and do not represent our
estimate or projection of the future common stock price. Actual gains, if any,
on stock option exercises are dependent on the future performance of the common
stock, overall market conditions and the option holder's continued employment
through the vesting period.

<TABLE>
<CAPTION>
                                    Individual Grants
                         ----------------------------------------
                                      % of
                                      Total                       Potential Realizable
                                     Options                        Value at Assumed
                         Number of   Granted                      Annual Rates of Stock
                         Securities    to     Exercise             Price Appreciation
                         Underlying Employees  Price                for Option Terms
                          Options   in Fiscal   Per    Expiration ---------------------
          Name            Granted     Year     Share      Date        5%        10%
          ----           ---------- --------- -------- ---------- ---------- ----------
<S>                      <C>        <C>       <C>      <C>        <C>        <C>
Russell J. Howard.......  172,500      5.8%    $0.75     9/08/09  $4,366,374 $7,029,354
 President, Chief
 Executive Officer and
 Director
Simba Gill..............  120,138      4.0      0.75     9/08/09   3,040,971  4,895,609
 Chief Financial Officer    6,600      0.2      0.50     3/24/09     168,711    270,599
 and Senior Vice
 President of Business
 Development
Michael Rabson..........  350,000     11.7      0.75     9/08/09   8,859,310 14,262,458
 Senior Vice President
 of Legal Affairs and
 General Counsel
Willem P.C. Stemmer.....  122,500      4.1      0.75     9/08/09   3,100,758  4,991,860
 Vice President of
 Research
John Bedbrook...........  200,000      6.7      7.50    11/10/09   3,712,463  6,799,976
 President of
 Agriculture
Norman Kruse............   46,543      1.6      0.75      9/8/09   1,178,111  1,896,622
 Director of               20,000      0.7      0.75     9/27/09     506,246    814,998
 Intellectual Property
 and Chief Patent
 Counsel
Joseph Affholter........   45,700      1.5      0.75      9/8/09   1,156,772  1,862,269
 Former Vice President     20,000      0.7      0.75     9/27/09     506,246    814,998
 of Biocatalysis
 and Chemicals
</TABLE>

                                       50
<PAGE>

   Aggregated Option Exercises in Fiscal Year 1999 and Fiscal-Year End Option
                                     Values

    The following table sets forth certain information regarding exercised
stock options during the fiscal year ended December 31, 1999 and unexercised
options held as of December 31, 1999 by each of the named executive officers.
We granted all options under our 1997 Stock Option Plan. These options are
immediately exercisable in full at the date of grant, but shares purchased on
exercise of unvested options are subject to a repurchase right in our favor
that entitles us to repurchase unvested shares at their original exercise price
on termination of the employee's services with us. Generally, the repurchase
right lapses as to 25% of the shares on the first anniversary of the grant date
and the balance, ratably by year, over the next three years. Under certain
circumstances the vesting of options, and consequently the lapse of the
repurchase right, may be accelerated. See "--Employee Benefit Plans--1997 Stock
Option Plan". The value realized is based on the fair market value of the
underlying securities as of the date of exercise, minus the per share exercise
price, multiplied by the number of shares underlying the option. The value of
unexercised in-the-money options are based on a value of $71.00 per share, the
last reported sale price of our common stock on the Nasdaq National Market on
December 31, 1999, minus the per share exercise price, multiplied by the number
of shares underlying the option. Each of the people below who exercised options
paid 10% of the exercise price by cash and the remaining amount with a full
recourse promissory note.

<TABLE>
<CAPTION>
                                                                                          Value of
                                                  Number of Securities            Unexercised In-The Money
                           Number of             Underlying Unexercised            Options at Fiscal Year-
                            Shares             Options at Fiscal Year-End                    End
                          Acquired on  Value   --------------------------------   -------------------------
          Name             Exercise   Realized Exercisable       Unexercisable    Exercisable Unexercisable
          ----            ----------- -------- ---------------   --------------   ----------- -------------
<S>                       <C>         <C>      <C>               <C>              <C>         <C>
Russell J. Howard
 President, Chief
 Executive Officer and
 Director...............     75,000   $33,750            297,500              --  $20,955,625     $ --
Simba Gill
 Chief Financial Officer
 and Senior Vice
 President of Business
 Development(1) ........    126,738     1,650                --               --          --        --
Michael Rabson
 Senior Vice President
 of Legal Affairs and
 General Counsel........    350,000       --                 --               --          --        --
Willem P.C. Stemmer
 Vice President of
 Research...............    122,500       --                 --               --          --        --
John Bedbrook
 President of
 Agriculture............        --        --             200,000              --   12,700,000       --
Norman Kruse
 Director of
 Intellectual Property,
 Chief Patent Counsel...    154,043    45,391                --               --          --        --
Joseph Affholter
 Former Vice President
 of Biocatalysis and
 Chemicals..............    175,700    49,500                --               --          --        --
</TABLE>
- --------
(1) Our right of repurchase lapses over a four-year period with respect to 25%
    of the underlying shares at the first anniversary of the grant date and in
    equal monthly installments over the next three years.

                                       51
<PAGE>

Employee Benefit Plans

 1997 Stock Option Plan

    Our board of directors adopted our 1997 Stock Option Plan on March 1, 1997.
This plan provides for the grant of incentive stock options to our employees
and nonstatutory stock options to our employees, directors and consultants. As
of February 15, 2000, 7,500,000 shares of common stock were reserved for
issuance under this plan. Of these shares, 2,111,602 shares were subject to
outstanding options and 1,243,385 shares were available for future grant. The
stock option plan provides for annual increases in the number of shares
available for issuance on the first day of each year, beginning January 1,
2001, equal to the lesser of 1,500,000 shares, 4% of the outstanding shares on
the date of the annual increase or an amount determined by our board of
directors.

    Our board of directors or a committee appointed by the board administers
the stock option plan and determines the terms of options granted, including
the exercise price, the number of shares subject to individual option awards
and the vesting period of options. The exercise price of nonstatutory options
must generally be at least 85% of the fair market value of the common stock on
the date of grant. The exercise price of incentive stock options cannot be
lower than 100% of the fair market value of the common stock on the date of
grant and, in the case of incentive stock options granted to holders of more
than 10% of our voting power, not less than 110% of the fair market value. The
term of an incentive stock option cannot exceed ten years, and the term of an
incentive stock option granted to a holder of more than 10% of our voting power
cannot exceed five years.

    A participant may not transfer rights granted under our stock option plan
other than by will, the laws of descent and distribution or as otherwise
provided under the stock option plan.

    Options granted under our stock option plan will accelerate and become
fully exercisable for a period of 30 days in the event we are acquired, unless
the successor corporation assumes or substitutes other equivalent options in
their place. Our board of directors may not, without the adversely affected
optionee's prior written consent, amend, modify or terminate the stock plan if
the amendment, modification or termination would impair the rights of
optionees. Our stock option plan will terminate in 2007 unless terminated
earlier by the board of directors.

    On September 8, 1999, the board of directors granted options to purchase an
aggregate of 187,387 shares of our common stock to our employees. These options
were granted under the 1997 Stock Option Plan and vest according to individual
schedules set by the board. The board of directors also retained the right to
accelerate vesting of these options based upon company-wide performance and the
performance of individual option holders. To date, the board has accelerated
portions of such options based on 1999 performance.

 1999 Employee Stock Purchase Plan

    Our board of directors adopted our 1999 Employee Stock Purchase Plan on
September 29, 1999. This plan provides our employees with an opportunity to
purchase our common stock through accumulated payroll deductions.

    A total of 400,000 shares of common stock has been reserved for issuance
under the purchase plan through March 2001. In addition, the purchase plan
provides for annual increases in the number of shares available for issuance
under the purchase plan on the first day of each year, beginning January 1,
2001, equal to the lesser of 200,000 shares, 0.75% of the outstanding shares on
the date of the annual increase or such amount as may be determined by the
board.

    The board of directors or a committee appointed by the board administers
the purchase plan. The board or its committee has full and exclusive authority
to interpret the terms of the purchase plan and determine eligibility.

                                       52
<PAGE>

    Employees are eligible to participate if they are customarily employed by
us or any participating subsidiary for at least 20 hours per week. However, an
employee may not be granted an option to purchase stock under the purchase
plan:

  . if such an employee immediately after grant owns stock possessing
    five percent or more of the total combined voting power or value
    of all classes of our capital stock, or

  . if, and to the extent that, such an employee has rights to
    purchase stock under all of our employee stock purchase plans in
    excess of $25,000 worth of stock for each calendar year.

    The purchase plan, which is intended to qualify under Section 423 of the
Internal Revenue Code of 1986, as amended, allows for favorable tax treatment
of participants, offering periods of up to 24 months, as determined by the plan
administrator, although it is anticipated that offering periods will generally
be 12 months, each including two six-month purchase periods. The offering
periods will generally start on the first trading day on or after April 1 of
each year, except for the first offering period which will commence on the
first trading day before the effective date of this offering, will end on the
last trading day on or before March 31, 2001, and will have two purchase
periods ending on the last trading days of September 2000 and March 2001.

    The purchase plan permits participants to purchase common stock though
payroll deductions of up to 15% of the participant's "compensation."
Compensation is defined as the participant's base straight time gross earnings
and commissions but excludes payments for overtime, shift premium payments,
incentive compensation, incentive payments, bonuses and other compensation.

    Amounts deducted and accumulated for the participant's account are used to
purchase shares of common stock on the last trading day of each purchase period
at a price of 85% of the lower of the fair market values of the common stock at
the beginning of the offering period and the end of the purchase period.
Participants may reduce their withholding percentage to zero at any time during
an offering period and may increase their withholding percentage or decrease
it, but to more than zero, on the first day of each purchase period.
Participants may end their participation at any time during an offering period,
and they will be paid their payroll deductions to date. Participation ends
automatically upon termination of employment with us.

    A participant may not transfer rights granted under the purchase plan other
than by will, the laws of descent and distribution or as otherwise provided
under the purchase plan.

    The purchase plan provides that, if we merge with or into another
corporation or a sale of substantially all of our assets, a successor
corporation may assume or substitute for each outstanding purchase right. If
the successor corporation refuses to assume or substitute for the outstanding
purchase rights, the offering period then in progress will be shortened, and a
new exercise date will be set.

    The purchase plan will terminate in 2009. However, the board of directors
has the authority to amend or terminate the purchase plan at any time and may
apply any action to affect their outstanding rights to purchase stock under the
purchase plan.

 1999 Nonemployee Directors Stock Option Plan

    We have adopted the 1999 Nonemployee Directors Stock Option Plan and have
reserved a total of 300,000 shares of common stock for issuance thereunder.
Maxygen will automatically grant each nonemployee director who becomes a
Maxygen director after our stockholder meeting in 2000 a nonstatutory stock
option to purchase 20,000 shares of common stock on the date on which such
person first becomes a director. At the first board of directors meeting
immediately following each annual stockholders meeting beginning with the 1999
Annual Stockholders Meeting, Maxygen will automatically

                                       53
<PAGE>

grant each nonemployee director a nonstatutory option to purchase 5,000 shares
of common stock. The exercise price of options under the director plan will be
equal to the fair market value of the common stock on the date of grant. The
maximum term of the options granted under the director plan is ten years.
Options will become exercisable at the rate determined by the plan
administrator. Shares underlying options granted to a director upon joining our
board are subject to a right of repurchase in our favor which lapses with
respect to 25% of the shares one year after the date of grant and at a rate of
25% of the shares at the end of each year thereafter. Each subsequent grant is
subject to a right of repurchase for one year after the date of grant. The
director plan will terminate in September 2009, unless terminated earlier in
accordance with the provisions of the director plan.

 401(k) Plan

    In May 1997, our board of directors adopted a Retirement Savings and
Investment Plan covering our full-time employees located in the United States.
This plan is intended to qualify under Section 401(k) of the Internal Revenue
Code of 1986, as amended, so that contributions to this plan by employees, and
the investment earnings thereon, are not taxable to employees until withdrawn.
Pursuant to the plan, employees may elect to reduce their current compensation
by up to the lesser of 25% of their annual compensation or the statutory
prescribed annual limit ($10,500 in 2000) and to have the amount of the
reduction contributed to the plan. We do not currently make additional matching
contributions on behalf of plan participants.

 Separation Arrangements

    In January 2000, Dr. Affholter resigned his position as Vice President of
Biocatalysis and Chemicals. In connection with his resignation, Dr. Affholter
entered into a separation agreement with Maxygen whereby Dr. Affholter received
acceleration of the vesting of options to purchase 20,675 shares of Maxygen's
common stock. He also retained his right to receive acceleration of options to
purchase up to 16,875 shares of Maxygen common stock under certain specified
circumstances. The agreement also provided for the restructuring of Dr.
Affholter's loan arrangements with Maxygen as described in "Related Party
Transactions". In connection with his resignation, Dr. Affholter entered into a
consulting agreement with Maxygen whereby he would remain as a consultant to
Maxygen through June 30, 2001. The agreement provides for consulting fees at an
hourly rate with minimum monthly hour requirements for each month of the
agreement. The agreement also provides for the vesting of 6,875 unvested
options on June 30, 2001 that were held by Dr. Affholter prior to his
resignation.

Limitation of Liability and Indemnification

    Our certificate of incorporation and bylaws limit the liability of
directors, officers, employees and other agents to the fullest extent permitted
by Delaware law; provided however that we indemnify any such person in
connection with a proceeding initiated by such person only if such proceeding
was authorized by our board. Delaware law provides that directors of a
corporation will not be personally liable for monetary damages for breach of
their fiduciary duties as directors, except for liability for: (1) breach of
their duty of loyalty to the corporation or its stockholders, (2) acts or
omissions not in good faith or which involve intentional misconduct or a
knowing violation of law, (3) unlawful payments of dividends or unlawful stock
repurchases or redemptions, or (4) any transaction from which the director
derived an improper personal benefit. This limitation of liability does not
apply to liabilities arising under the federal or state securities laws and
does not affect the availability of equitable remedies such as injunctive
relief or rescission.

    We believe that indemnification under our bylaws and certificate of
incorporation covers at least negligence and gross negligence on the part of
indemnified parties. Our bylaws also permit us to secure insurance on behalf of
any officer, director, employee or other agent for any liability arising out of
his or her actions in this capacity, regardless of whether the bylaws permit
indemnification. We have obtained directors' and officers' liability insurance
to cover certain liabilities described above.

                                       54
<PAGE>

    We intend to enter into agreements to indemnify our officers and directors,
in addition to the indemnification provided for in our bylaws. These
agreements, among other things, will indemnify our officers and directors for
certain expenses (including attorneys' fees), judgments, fines and settlement
amounts incurred by any such person in any action or proceeding, including any
action by or in the right of Maxygen arising out of such person's services as
one of our directors or such person's services to any of our subsidiaries or
any other company or enterprise to which the person provides services at our
request. We believe that these provisions and agreements are necessary to
attract and retain qualified persons as directors.

    There is no pending litigation or proceeding involving a director or
officer of Maxygen in which indemnification is required or permitted, and we
are not aware of any threatened litigation or proceeding that may result in a
claim for indemnification.

                                       55
<PAGE>

                           RELATED PARTY TRANSACTIONS

    Since inception (May 1996), there has not been, nor is there currently
proposed, any transaction or series of similar transactions to which we were or
are to be a party in which the amount involved exceeds $60,000 and in which any
current director, executive officer or holder of more that 5% of our common
stock had or will have a direct or indirect interest other than (1)
compensation arrangements, which are described where required under
"Management" and (2) the transactions described below.

    In February 1997, we entered into a services agreement with Affymax
Research Institute. Pursuant to the services agreement, Affymax provided
certain accounting, administrative and facilities management services to us and
allowed us to occupy certain facilities leased by Affymax in exchange for
specified annual fees. The services agreement terminated on April 1, 1999.

    At the time of our formation, we entered into a technology transfer
agreement with Affymax Technologies N.V. and Glaxo Group Limited, each a
wholly-owned subsidiary of Glaxo Wellcome plc, pursuant to which we were
assigned all right, title and interest in the patents, patent applications and
confidential information relating to our MolecularBreeding directed molecular
evolution technologies, subject to an exclusive royalty-free license under the
patents and patent applications for use in the diagnostics and research supply
markets for specific applications. In exchange for the intellectual property
transferred we issued 5,460,000 shares of our common stock to Affymax.

    In March 1997, in connection with our formation, we made loans to certain
officers and directors to purchase our common stock, which are evidenced by
full recourse promissory notes and secured by the common stock underlying this
stock purchase. The promissory notes bear interest at 6.42% per year, and
interest payments on the notes are due and payable on June 30 and December 31
of each year. Unpaid principal and interest on the notes are due and payable on
the earlier of 30 days after termination of the participant's employment,
directorship or consultancy with us, or three years after the date of the
promissory note. As of February 15, 2000, the original and outstanding
principal amounts of each promissory note by a director or executive officer
are set forth below.

<TABLE>
<CAPTION>
                                                            Original
                                                              Note   Outstanding
                Director or Executive Officer                Amount  Note Amount
                -----------------------------               -------- -----------
   <S>                                                      <C>      <C>
   Russell J. Howard ...................................... $ 60,000  $ 60,000
   Isaac Stein.............................................  120,000         0
   Willem P.C. Stemmer.....................................  120,000   120,000
</TABLE>

                                       56
<PAGE>

    Options granted to our directors, executive officers and key employees are
immediately exercisable as to both vested and unvested shares, with unvested
shares being subject to a right of repurchase in our favor in the event of
termination of employment prior to vesting of all shares. These individuals pay
the exercise price for their outstanding options pursuant to full recourse
promissory notes secured by the common stock underlying the options. The notes
bear interest at 5.59% per year, and interest payments on the notes are due and
payable on June 30 and December 31 of each year. Unpaid principal and interest
on the notes are due and payable on the earlier of 30 days after termination of
the participant's employment, directorship or consultancy with us, or three
years after the date of the promissory note. As of February 15, 2000, the
original and outstanding principal amounts of each promissory note by a
director or executive officer are set forth below.

<TABLE>
<CAPTION>
                                                                      Original
                                                                         and
                                                                     Outstanding
                     Director or Executive Officer                   Note Amount
                     -----------------------------                   -----------
   <S>                                                               <C>
   Joseph Affholter(1)..............................................  $ 23,141
   Simba Gill.......................................................   173,163
   Russell J. Howard................................................    47,250
   Norman Kruse.....................................................    56,728
   Michael S. Rabson................................................   236,250
   Gordon Ringold...................................................    99,000
   Howard Simon.....................................................   259,875
   Willem P.C. Stemmer..............................................   136,688
</TABLE>
- --------
(1) Unpaid principal and interest under Dr. Affholter's notes are due and
    payable on June 30, 2002.

    In April 1998, we loaned $72,500 to Dr. Joseph Affholter, which is
evidenced by a full recourse promissory note. In April 1999, we loaned an
additional $77,500 to Dr. Affholter and received from Dr. Affholter a full
recourse promissory note covering all amounts due from Dr. Affholter, which
note was secured by a deed of trust on Dr. Affholter's principal residence and
bore interest at 5.70% per year with respect to $72,500 of the principal and
4.83% with respect to $77,500 of the principal. Under the terms of the
promissory note, interest was generally forgiven. The promissory note was due
with respect to $72,500 of the principal on April 1, 2003 and with respect to
$77,500 of the principal on March 30, 2004. In connection with Dr. Affholter's
resignation in January 2000, the loans were converted into a personal loan of
$150,000, with interest calculated semi-annually from February 1, 2001 at
5.59%. The arrangements also defer payment of such loan until April 1, 2003
with respect to $72,500 of the principal and until March 30, 2004 with respect
to $77,500 of the principal. The loan is secured by a pledge of vested shares
of Maxygen common stock valued at $300,000 as of the date of the loan
conversion.

    In March 1997, December 1997 and April 1998, we sold to various investors a
total of 2,795,000 shares of Series A preferred stock at a purchase price of
$2.00 per share. In August 1998, we sold to various investors a total of
3,666,667 shares of Series B preferred stock at a purchase price of $3.00 per
share. In December 1998, we sold to a collaborator a total 1,000,000 shares of
Series C preferred stock at a purchase price of $5.00 per share. In June 1999,
we sold to various investors a total of 3,636,364 shares of Series D preferred
stock at a purchase price of $5.50 per share. In August 1999, we sold to a
collaborator a total of 800,000 shares of Series E preferred stock at a
purchase price of $6.25. Upon the initial public offering, each share of
preferred stock was converted into one share of common stock. Holders of the
converted common stock are entitled to registration rights. See "Description of
Capital Stock--Registration Rights."

                                       57
<PAGE>

    The table below sets forth our current officers, directors, immediate
family members of officers and directors and holders of more than 5% of our
outstanding stock who since January 1, 1997 invested in, or became beneficial
owners of our common stock issued upon conversion of our preferred stock.

<TABLE>
<CAPTION>
                             Stockholder                            Common Stock
                             -----------                            ------------
   <S>                                                              <C>
   Holders of More than 5%:
     Glaxo Wellcome International B.V..............................  1,250,000
     Technogen Associates, L.P. (1)................................  3,274,772
     Technogen Enterprises, L.L.C. (2).............................  3,274,772
   Directors:
     Gordon Ringold (3)............................................  3,291,439
     Isaac Stein (4)...............................................  3,348,106
   Officers:
     Russell Howard (5)............................................     55,136
     Willem Stemmer................................................    125,000
     Michael Rabson................................................      9,100
   Immediate Family Members of Officers and Directors:
     Bhagwant Gill and Krishna Gill (6)............................    128,787
     Joseph Glaser, II (7).........................................      8,712
     Robert Glaser, Jr. (8)........................................     10,991
     Sally Glaser (9)..............................................      9,718
</TABLE>
- --------
(1) Consists of 3,211,574 shares held by Technogen Associates, L.P. and 63,198
    shares held by Technogen Enterprises, L.L.C. Technogen Enterprises, L.L.C.
    and Technogen Associates, L.P. are under common control.

(2) Consists of 3,211,574 shares held by Technogen Associates, L.P. and 63,198
    shares held by Technogen Enterprises, L.L.C. Technogen Enterprises, L.L.C.
    and Technogen Associates, L.P. are under common control.

(3) Includes 3,211,574 shares held by Technogen Associates, L.P. and 63,198
    shares held by Technogen Enterprises, L.L.C. Technogen Managers, L.L.C. is
    the general partner of Technogen Associates, L.P. Dr. Ringold is a Managing
    Member of Technogen Enterprises, L.L.C. and Technogen Managers, L.L.C. and
    disclaims beneficial ownership of these shares except to the extent of his
    pecuniary interest in the limited liability companies.

(4) Includes 3,211,574 shares held by Technogen Associates, L.P. and 63,198
    shares held by Technogen Enterprises, L.L.C. Technogen Managers, L.L.C. is
    the general partner of Technogen Associates, L.P. Mr. Stein is a Managing
    Member of Technogen Enterprises, L.L.C. and Technogen Managers, L.L.C. and
    disclaims beneficial ownership of these shares except to the extent of his
    pecuniary interest in the limited liability companies. Also includes
    525,667 shares held by the Stein 1995 Revocable Trust, of which Mr. Stein
    is a trustee and 41,667 shares held by Stein Partners, of which Mr. Stein
    is a general partner.

(5) Includes 53,636 shares held by the Russell and Maureen Howard Trust, of
    which Dr. Howard is a trustee.

(6) Drs. Gill are the parents of Simba Gill.

(7) Mr. Glaser is the son of Robert J. Glaser.

(8) Mr. Glaser is the son of Robert J. Glaser.

(9) Ms. Glaser is the daughter of Robert J. Glaser.

    We believe that all transactions between us and our officers, directors,
principal stockholders and other affiliates have been and will be on terms no
less favorable to us than could be obtained from unaffiliated third parties.

                                       58
<PAGE>

                             PRINCIPAL STOCKHOLDERS

    The following table sets forth the beneficial ownership of our common stock
as of February 15, 2000 by:

  . each person who is known by us to beneficially own more than 5% of our
    common stock;

  . each of the named executive officers and each of our directors; and

  . all of our executive officers and directors as a group.

    Percentage of ownership is based on 30,769,644 shares outstanding as of
February 15, 2000, and 32,269,644 shares outstanding after this offering,
assuming no exercise of the underwriters' over-allotment options. Beneficial
ownership is calculated based on SEC requirements. All shares of the common
stock subject to options currently exercisable or exercisable within 60 days
after February 15, 2000 are deemed to be outstanding for the purpose of
computing the percentage of ownership of the person holding such options, but
are not deemed to be outstanding for computing the percentage of ownership of
any other person. Unless otherwise indicated below, each stockholder named in
the table has sole or shared voting and investment power with respect to all
shares beneficially owned, subject to applicable community property laws.
Unless otherwise indicated in the table, the address of each individual listed
in the table is Maxygen, Inc., 515 Galveston Drive, Redwood City, California
94063.

<TABLE>
<CAPTION>
                                       Number of    Percentage of Shares
                                         Shares      Beneficially Owned
                                      Beneficially  ------------------------
                                     Owned Prior to   Before        After
         Beneficial Owner             the Offering   Offering      Offering
         ----------------            -------------- ----------    ----------
<S>                                  <C>            <C>           <C>
Glaxo Wellcome International BV        6,785,000            22.1%         21.0%
 (1)...............................
 Huis ter Heideweg 62 3705 LZ Zeist
 The Netherlands
Technogen Associates, L.P. (2).....    3,274,772            10.6          10.1
 525 University Avenue, Suite 700
 Palo Alto, California 94301
Technogen Enterprises, L.L.C. (3)..    3,274,772            10.6          10.1
 525 University Avenue, Suite 700
 Palo Alto, California 94301
Russell J. Howard, Ph.D. (4).......      877,636             2.9           2.7
Willem P.C. Stemmer, Ph.D. (5).....    1,147,500             3.7           3.6
Simba Gill, Ph.D. (6)..............      456,738             1.5           1.4
John Bedbrook, Ph.D. (7)...........      203,000              *             *
Norman Kruse, Ph.D. (8)............      149,375              *             *
Michael Rabson, Ph.D. (9) .........      361,100             1.2           1.1
Isaac Stein (10)...................    3,862,106            12.6          12.0
Robert J. Glaser, M.D..............           --              *             *
M.R.C. Greenwood, Ph.D. (11).......       75,000              *             *
Adrian Hennah (12).................       75,000              *             *
George Poste, Ph.D. (13)...........       75,000              *             *
Gordon Ringold, Ph.D. (14).........    3,821,439            12.4          11.8
Joseph Affholter, Ph.D. (15).......       67,313              *             *
All directors and executive
 officers as a group (14 persons)
 (16)..............................    8,076,303            26.2          25.0
</TABLE>
- --------
*Less than 1% of Maxygen's outstanding common stock.

(1) Includes 75,000 shares subject to immediately exercisable options held by
    Adrian Hennah and which Mr. Hennah has assigned to Glaxo Wellcome plc which
    is the parent of Glaxo Wellcome International BV.

(2) Consists of 3,211,574 shares held by Technogen Associates, L.P. and 63,198
    shares held by Technogen Enterprises, L.L.C. Technogen Enterprises, L.L.C.
    and Technogen Associates, L.P. are under common control.

(3) Consists of 3,211,574 shares held by Technogen Associates, L.P. and 63,198
    shares held by Technogen Enterprises, L.L.C. Technogen Enterprises, L.L.C.
    and Technogen Associates, L.P. are under common control.

                                       59
<PAGE>

(4) Includes 53,636 shares held by the Russell and Maureen Howard Trust, of
    which Dr. Howard is a trustee. Also includes 297,500 shares that are
    subject to immediately exercisable options. As of February 15, 2000, we
    have the right to repurchase 444,375 shares including shares issuable upon
    exercise of options held by Dr. Howard if Dr. Howard ceases his employment,
    directorship or consultancy with us.

(5) Includes 352,187 shares that are subject to our right of repurchase as of
    February 15, 2000 if Dr. Stemmer ceases his employment, directorship or
    consultancy with us.

(6) Includes 307,537 shares that are subject to our right of repurchase as of
    February 15, 2000 if Dr. Gill ceases his employment, directorship or
    consultancy with us.

(7) Includes 200,000 shares that are subject to immediately exercisable
    options. As of February 15, 2000, we have the right to repurchase all of
    the shares issuable upon exercise of these options if Dr. Bedbrook ceases
    his employment, directorship or consultancy with us.

(8) Includes 127,500 shares that are subject to our right of repurchase as of
    February 15, 2000 if Dr. Kruse ceases his employment, directorship or
    consultancy with us.

(9)  As of February 15, 2000, we have the right to repurchase 350,000 of these
     shares if Dr. Rabson ceases his employment, directorship or consultancy
     with us.

(10) Includes 3,211,574 shares that are held by Technogen Associates, L.P. and
     63,198 shares held by Technogen Enterprises, L.L.C. Technogen Managers,
     L.L.C. is the general partner of Technogen Associates, L.P. Mr. Stein is a
     Managing Member of Technogen Enterprises, L.L.C. and Technogen Managers,
     L.L.C. and disclaims beneficial ownership of these shares except to the
     extent of his pecuniary interest in the limited liability companies.
     Includes 525,667 shares held by the Stein 1995 Revocable Trust, of which
     Mr. Stein is a trustee and 41,667 shares held by Stein Partners, of which
     Mr. Stein is a general partner. As of February 15, 2000, we have the right
     to repurchase 162,500 shares held by Mr. Stein if he ceases his
     employment, directorship or consultancy with us.

(11) Includes 75,000 shares that are subject to immediately exercisable
     options. As of February 15, 2000, we have the right to repurchase 56,250
     shares issuable upon exercise of these options if Dr. Greenwood ceases her
     employment, directorship or consultancy with us.

(12) Includes 75,000 shares that are subject to immediately exercisable
     options. As of February 15, 2000, we have the right to repurchase 37,500
     shares issuable upon exercise of these options if Mr. Hennah ceases his
     employment, directorship or consultancy with us. Mr. Hennah has assigned
     beneficial ownership of these shares to Glaxo Wellcome plc and disclaims
     beneficial ownership of the shares.

(13) Includes 75,000 shares that are subject to immediately exercisable
     options. As of February 15, 2000, we have the right to repurchase all of
     the shares issuable upon exercise of these options if Dr. Poste ceases his
     employment, directorship or consultancy with us.

(14) Includes 3,211,574 shares held by Technogen Associates, L.P. and 63,198
     shares held by Technogen Enterprises, L.L.C. Technogen Managers, L.L.C. is
     the general partner of Technogen Associates, L.P. Dr. Ringold is a
     Managing Member of Technogen Enterprises, L.L.C. and Technogen Managers,
     L.L.C. and disclaims beneficial ownership of these shares except to the
     extent of his pecuniary interest in the limited liability companies. Also
     includes 20,000 shares held by the Gregory Zarucki Ringold 1998 Trust,
     20,000 shares held by the Alexander Zarucki Ringold 1998 Trust and 20,000
     shares held by the Melanie Gault-Ringold 1998 Trust. As of February 15,
     2000, we have the right to repurchase 137,500 shares held by Dr. Ringold
     if he ceases his employment, directorship or consultancy with us.

(15) Includes 6,875 shares that are subject to our right of repurchase as of
     February 15, 2000 if Dr. Affholter ceases his employment, directorship or
     consultancy with us.

(16) Includes shares included pursuant to notes (2), (3), (4), (5), (6), (7),
     (8), (9), (10), (11), (12), (13), (14) and (15), 175,200 shares
     beneficially owned by Howard Simon, of which 136,500 shares are subject to
     immediately exercisable options and 38,500 shares are subject to our right
     of repurchase as of February 15, 2000.

                                       60
<PAGE>

                          DESCRIPTION OF CAPITAL STOCK

General

    Our amended and restated certificate of incorporation authorizes the
issuance of up to 70,000,000 shares of common stock, par value $0.0001 per
share, and 5,000,000 shares of preferred stock, par value $0.0001 per share,
the rights and preferences of which may be established from time to time by our
board of directors. As of February 15, 2000, we had outstanding 30,769,644
shares of common stock held by approximately 313 holders of record.

Common Stock

    Each holder of common stock is entitled to one vote for each share on all
matters to be voted upon by the stockholders and there are no cumulative voting
rights. Subject to preferences to which holders of preferred stock issued after
the sale of the common stock offered hereby may be entitled, holders of common
stock are entitled to receive ratably such dividends, if any, as may be
declared from time to time by the board of directors out of funds legally
available therefor. In the event of our liquidation, dissolution or winding up,
holders of common stock will be entitled to share in our assets remaining after
the payment of liabilities and the satisfaction of any liquidation preference
granted to the holders of any outstanding shares of preferred stock. Holders of
common stock have no preemptive or conversion rights or other subscription
rights, and there are no redemption or sinking fund provisions applicable to
the common stock. All outstanding shares of common stock are, and the shares of
common stock offered by us in this offering, when issued and paid for, will be,
fully paid and nonassessable. The rights, preferences and privileges of the
holders of common stock are subject to, and may be adversely affected by, the
rights of the holders of shares of any series of preferred stock, which we may
designate in the future.

Preferred Stock

    Our board of directors is authorized, subject to any limitations prescribed
by law, without stockholder approval, from time to time to issue up to an
aggregate of five million shares of preferred stock, $0.0001 par value per
share, in one or more series, each of such series to have such rights and
preferences, including voting rights, dividend rights, conversion rights,
redemption privileges and liquidation preferences, as shall be determined by
the board of directors. The rights of the holders of common stock will be
subject to, and may be adversely affected by, the rights of holders of any
preferred stock that may be issued in the future. Issuance of preferred stock,
while providing desirable flexibility in connection with possible acquisitions
and other corporate purposes, could have the effect of making it more difficult
for a third party to acquire, or of discouraging a third party from attempting
to acquire, a majority of our outstanding voting stock. We have no present
plans to issue any shares of preferred stock.

Registration Rights

    Pursuant to a registration rights agreement entered into between us and
holders of 19,458,031 shares of common stock issued upon conversion of our
Series A, Series B, Series C, Series D and Series E preferred stock, we are
obligated, under limited circumstances and subject to specified conditions and
limitations, to use our reasonable best efforts to register the registrable
shares.

    We must use our reasonable best efforts to register shares of the
registrable shares:

  -  if we receive written notice from holders of 50% or more of the
     registrable shares requesting that we effect a registration with respect
     to at least 20% of the registrable shares then held by the holders
     requesting registration;

  -  if we decide to register our own securities; or

  -  if (1) we receive written notice from any holder or holders of the
     registrable shares requesting that we effect a registration on Form S-3
     (a shortened form of registration statement) with respect to the
     registrable shares and (2) we are then eligible to use Form S-3 (which
     at the earliest could occur 12 calendar months after the closing of this
     offering).

                                       61
<PAGE>

   However, in addition to certain other conditions and limitations, if we are
proposing to issue registered shares and the underwriters request to decrease
the number of shares registered, we can limit the number of registerable
shares included in the registration statement. The underwriters have requested
that no registerable shares be registered in this offering. In addition, the
holders of these registration rights have entered into lockup agreements and
waived their registration rights until 180 days following this offering.

Anti-Takeover Provisions

 Charter and Bylaw Provisions

   Certain provisions of our certificate of incorporation and bylaws may have
the effect of making it more difficult for a third party to acquire, or of
discouraging a third party from attempting to acquire, control of us. Such
provisions could limit the price that certain investors might be willing to
pay in the future for shares of our common stock. Certain of these provisions
allow us to issue preferred stock without any vote or further action by the
stockholders, require advance notification of stockholder proposals and
nominations of candidates for election as directors, and eliminate cumulative
voting in the election of directors. In addition, our bylaws provide that
special meetings of the stockholders may be called only by the board of
directors and that the authorized number of directors may be changed only by
resolution of the board of directors. These provisions may make it more
difficult for stockholders to take certain corporate actions and could have
the effect of delaying or preventing a change in control of Maxygen.

 Delaware Law

   We are subject to Section 203 of the Delaware General Corporation Law. This
law prohibits a Delaware corporation from engaging in any business combination
with any interested stockholder, unless any of the following conditions are
met. First, this law does not apply if prior to the date of the transaction,
the board of directors of the corporation approved either the business
combination or the transaction which resulted in the stockholder becoming an
interested stockholder. Second, the law does not apply if upon consummation of
the transaction which resulted in the stockholder becoming an interested
stockholder, the interested stockholder owned at least 85% of the voting stock
of the corporation outstanding at the time the transaction commenced,
excluding for purposes of determining the number of shares outstanding those
shares owned by persons who are directors and also officers and by employee
stock plans in which employee participants do not have the right to determine
confidentially whether shares held subject to the plan will be tendered in a
tender or exchange offer. Third, the law does not apply if at or after the
date of the transaction, the business combination is approved by the board of
directors and authorized at an annual or special meeting of stockholders, and
not by written consent, by the affirmative vote of at least 66 2/3% of the
outstanding voting stock which is not owned by the interested stockholder.

Transfer Agent and Registrar

   The Transfer Agent and Registrar for our common stock is ChaseMellon
Shareholder Services, L.L.C.

                                      62
<PAGE>

                        SHARES ELIGIBLE FOR FUTURE SALE

   Future sales of substantial amounts of common stock in the public market
could adversely affect the market price of our common stock.

   Upon completion of this offering, we will have outstanding an aggregate of
32,269,644 shares of common stock, assuming the issuance of 1,500,000 shares
of common stock offered hereby and no exercise of options after February 15,
2000. Of the 6,900,000 shares sold in our initial public offering, 1,500,000
shares sold in this offering and 17,250 shares issued upon exercise of options
between December 22, 1999 and February 15, 2000, 7,232,134 shares will be
freely tradable without restriction or further registration under the
Securities Act, except for any shares held by "affiliates" of Maxygen as that
term is defined in Rule 144 under the Securities Act, 1,167,866 shares will be
subject to lock-up agreements providing that the stockholders will not offer,
sell or otherwise dispose of any of the shares of common stock owned by them
until 90 days after the date of this prospectus and 17,250 shares will be
subject to lock-up agreements which expire on June 12, 2000. Shares purchased
by affiliates may generally only be sold pursuant to an effective registration
statement under the Securities Act or in compliance with limitations of Rule
144 as described below.

   The remaining 23,852,394 shares of common stock were issued and sold by us
in reliance on exemptions from the registration requirements of the Securities
Act. All of these shares are subject to "lock-up" agreements entered into in
connection with our initial public offering providing that the stockholder
will not offer, sell or otherwise dispose of any of the shares of common stock
owned by them before June 13, 2000. Additionally, our directors, officers and
certain stockholders, including greater than 5% stockholders, who collectively
hold 15,711,973 shares of our common stock have entered into lock-up
agreements in connection with this offering. These lock-up agreements expire
on the 90th day following the date of this prospectus. Goldman, Sachs & Co.,
however, may in its sole discretion, at any time without notice, release all
or any portion of the shares subject to lock-up agreements. Upon expiration of
the lock-up agreements, these shares will become eligible for sale pursuant to
Rule 144(k), Rule 144 and Rule 701 as discussed below.

   We have in effect a registration statement under the Securities Act
registering the shares to be issued under our stock option plans. As a result,
any options exercised under the stock option plans or issued under any other
benefit plan since the filing of the registration statement governing our
benefit plans will be freely tradeable in the public market after the
expiration the 180 day lock-ups entered into in connection with our initial
public offering, except that shares held by affiliates will still be subject
to the limitations of Rule 144.

   Also beginning three months after the date of this offering, holders of
19,458,031 shares of our common stock will be entitled to certain rights with
respect to registration of these shares for sale in the public market. See
"Description of Capital Stock -- Registration Rights". Registration of these
shares under the Securities Act would result in these shares becoming freely
tradable without restriction under the Securities Act immediately upon
effectiveness of the registration.

Rule 144

   In general, under Rule 144 as currently in effect, subject to the
provisions of any lock-up agreements, a person who has beneficially owned
shares of our common stock for at least one year would be entitled to sell in
"broker's transactions" or to market makers, within any three-month period, a
number of shares that does not exceed the greater of:

  - 1% of the number of shares of common stock then outstanding (which will
  equal approximately 322,696 shares immediately after this offering); or

  - the average weekly trading volume in the common stock on the Nasdaq
  National Market during the four calendar weeks preceding the filing of a
  notice on Form 144 with respect to such sale.

                                      63
<PAGE>

    Sales under Rule 144 are generally subject to the availability of current
public information about Maxygen.

Rule 144(k)

    Under Rule 144(k), a person who is not deemed to have been our affiliate at
any time during the 90 days preceding a sale, and who has beneficially owned
the shares proposed to be sold for at least two years, is entitled to sell such
shares without having to comply with the manner of sale, public information,
volume limitation or notice filing provisions of Rule 144. Therefore, "144(k)
shares" may be sold immediately upon expiration of the lock-up agreements.

Rule 701

    In general, under Rule 701, any of our employees, directors, officers,
consultants or advisors who purchase shares from us in connection with a
compensatory stock or option plan or other written agreement before the
effective date of our initial public offering is entitled to sell such shares
in reliance on Rule 144, in the case of affiliates, without having to comply
with the holding period and notice filing requirements of Rule 144 and, in the
case of non-affiliates, without having to comply with the public information,
volume limitation or notice filing requirements of Rule 144.

                                 LEGAL MATTERS

    The validity of the common stock offered hereby will be passed upon for
Maxygen by Heller Ehrman White & McAuliffe, Palo Alto, California. Certain
legal matters will be passed upon for the underwriters by Wilson Sonsini
Goodrich & Rosati, Professional Corporation. An investment partnership composed
of current and former members of and persons associated with Wilson Sonsini
Goodrich & Rosati, Professional Corporation, beneficially own 4,546 shares of
our common stock. Heller Ehrman White & McAuliffe, certain of its employees and
HEWM Investors, an entity affiliated with Heller Ehrman White & McAuliffe,
beneficially own 35,000 shares of our common stock. Julian N. Stern, the sole
shareholder of a professional corporation that is a partner of Heller Ehrman
White & McAuliffe and Secretary of Maxygen beneficially owns 66,000 shares of
our common stock.

                                    EXPERTS

    Ernst & Young LLP, independent auditors, have audited our financial
statements at December 31, 1998 and 1999, and for the each of the three years
in the period ended December 31, 1999 as set forth in their report. We have
included our financial statements in the prospectus and elsewhere in the
registration statement in reliance on Ernst & Young LLP's report, given upon
the authority of such firm as experts in accounting and auditing.

                                       64
<PAGE>

                   WHERE YOU CAN FIND ADDITIONAL INFORMATION

    We have filed with the SEC a registration statement on Form S-1 (including
exhibits and schedules) under the Securities Act, with respect to the shares to
be sold in this offering. This prospectus does not contain all of the
information set forth in the registration statement. For further information
with respect to us and the common stock offered in this prospectus, reference
is made to the registration statement, including the exhibits, financial
statements and notes to the financial statements filed as a part of the
registration statement. You should read the documents filed with the SEC as
exhibits to the registration statement for a more complete description of the
matter involved.

    We will be filing quarterly and annual reports, proxy statements and other
information with the SEC. You may read and copy any document that we file at
the public reference facilities of the SEC at Room 1024, 450 Fifth Street,
N.W., Washington, D.C. 20549. Please call the SEC at 1-800-SEC-0330 for further
information on the public reference rooms. Our SEC filings are also available
to the public from the SEC's web site at http://www.sec.gov.

                                       65
<PAGE>

                                 MAXYGEN, INC.

                         INDEX TO FINANCIAL STATEMENTS

<TABLE>
<S>                                                                        <C>
Report of Ernst & Young LLP Independent Auditors..........................  F-2
Balance Sheets............................................................  F-3
Statements of Operations..................................................  F-4
Statement of Stockholders' Equity.........................................  F-5
Statements of Cash Flows..................................................  F-6
Notes to Financial Statements.............................................  F-7
</TABLE>

                                      F-1
<PAGE>

               REPORT OF ERNST & YOUNG LLP, INDEPENDENT AUDITORS

The Board of Directors and Stockholders
Maxygen, Inc.

   We have audited the accompanying balance sheets of Maxygen, Inc. as of
December 31, 1998 and 1999, and the related statements of operations,
stockholders' equity, and cash flows for each of the three years in the period
ended December 31, 1999. These financial statements are the responsibility of
the Company's management. Our responsibility is to express an opinion on these
financial statements based on our audits.

   We conducted our audits in accordance with auditing standards generally
accepted in the United States. Those standards require that we plan and perform
the audit to obtain reasonable assurance about whether the financial statements
are free of material misstatement. An audit includes examining, on a test
basis, evidence supporting the amounts and disclosures in the financial
statements. An audit also includes assessing the accounting principles used and
significant estimates made by management, as well as evaluating the overall
financial statement presentation. We believe that our audits provide a
reasonable basis for our opinion.

   In our opinion, the financial statements referred to above present fairly,
in all material respects, the financial position of Maxygen, Inc. at December
31, 1998 and 1999, and the results of its operations and its cash flows for
each of the three years in the period ended December 31, 1999 in conformity
with accounting principles generally accepted in the United States.

                                        /s/ Ernst & Young LLP

Palo Alto, California
February 18, 2000

                                      F-2
<PAGE>

                                 MAXYGEN, INC.

                                 BALANCE SHEETS
               (in thousands, except share and per share amounts)

<TABLE>
<CAPTION>
                                                                December 31,
                                                              -----------------
                                                               1998      1999
                                                              -------  --------
<S>                                                           <C>      <C>
ASSETS
Current assets:
  Cash and cash equivalents.................................  $15,306  $136,343
  Grant and other receivables...............................      600     3,038
  Prepaid expenses and other current assets.................      271       800
                                                              -------  --------
   Total current assets.....................................   16,177   140,181
  Property and equipment, net...............................    1,001     4,764
  Deposits and other assets.................................      422       633
                                                              -------  --------
   Total assets.............................................  $17,600  $145,578
                                                              =======  ========

LIABILITIES AND STOCKHOLDERS' EQUITY
Current liabilities:
  Accounts payable..........................................     $466      $370
  Accrued compensation......................................      153       393
  Other accrued liabilities.................................      286     1,803
  Deferred revenue..........................................    2,903     4,935
  Related party payables....................................      105       --
  Current portion of equipment financing obligations........      --        170
                                                              -------  --------
Total current liabilities...................................    3,913     7,671
Deferred revenue............................................    1,987     2,527
Non-current portion of equipment financing obligations .....      --      1,664
Commitments
Stockholders' equity:
  Convertible preferred stock, $0.0001 par value,
   25,000,000 shares and 5,000,000 shares authorized at
   December 31, 1998 and 1999, respectively, 7,461,667 and
   no shares issued and outstanding at December 31, 1998 and
   1999, respectively  .....................................        1       --
  Common stock, $0.0001 par value: 70,000,000 shares
   authorized, 9,230,500, and 30,860,781 shares issued and
   outstanding at December 31, 1998 and 1999, respectively..        1         3
  Additional paid-in capital................................   27,706   176,517
  Notes receivable from stockholders........................     (548)   (1,411)
  Deferred stock compensation...............................   (2,601)  (17,216)
  Accumulated deficit.......................................  (12,859)  (24,177)
                                                              -------  --------
   Total stockholders' equity...............................   11,700   133,716
                                                              -------  --------
   Total liabilities and stockholders' equity...............  $17,600  $145,578
                                                              =======  ========
</TABLE>

                            See accompanying notes.

                                      F-3
<PAGE>

                                 MAXYGEN, INC.

                            STATEMENTS OF OPERATIONS
                     (in thousands, except per share data)

<TABLE>
<CAPTION>
                                                     Year ended December 31,
                                                     --------------------------
                                                      1997     1998      1999
                                                     -------  -------  --------
<S>                                                  <C>      <C>      <C>
Collaborative research and development revenue.....     $341   $1,077    $8,895
Grant revenue......................................      --     1,646     5,122
                                                     -------  -------  --------
Total revenues.....................................      341    2,723    14,017
Operating expenses:
  Research and development (Including charges for
   stock compensation of $317, $651 and $3,998 in
   1997, 1998 and 1999, respectively)..............    3,074    7,858    19,250
  General and administrative (Including charges for
   stock compensation of $546, $910 and $2,501 in
   1997, 1998 and 1999, respectively)..............    1,461    3,920     7,498
                                                     -------  -------  --------
Total operating expenses...........................    4,535   11,778    26,748
                                                     -------  -------  --------
Loss from operations...............................   (4,194)  (9,055)  (12,731)
Interest income (expense), net.....................      161      229     1,413
                                                     -------  -------  --------
Net loss...........................................   (4,033)  (8,826)  (11,318)
Deemed dividend upon issuance of convertible
 preferred stock (Note 8)..........................      --       --     (2,200)
                                                     -------  -------  --------
Net loss attributable to common stockholders.......  $(4,033) $(8,826) $(13,518)
                                                     =======  =======  ========
Basic and diluted net loss per share...............   $(0.82)  $(1.31)   $(1.53)
                                                     =======  =======  ========
Shares used in computing basic and diluted net loss
 per share.........................................    4,917    6,748     8,854
</TABLE>


                            See accompanying notes.

                                      F-4
<PAGE>

                                 MAXYGEN, INC.
                       STATEMENT OF STOCKHOLDERS' EQUITY
               (in thousands, except share and per share amounts)
<TABLE>
<CAPTION>
                       Convertible                                      Notes
                     Preferred Stock      Common Stock    Additional  Receivable    Deferred                   Total
                    ------------------- -----------------  Paid-In       from        Stock     Accumulated Stockholders'
                      Shares     Amount   Shares   Amount  Capital   Stockholders Compensation   Deficit      Equity
                    -----------  ------ ---------- ------ ---------- ------------ ------------ ----------- -------------
<S>                 <C>          <C>    <C>        <C>    <C>        <C>          <C>          <C>         <C>
Issuance of common
stock to Affymax
Technologies N.V.
and Glaxo Group
Limited for
technology in
March 1997........          --    $ --   5,460,000 $ --    $    --     $   --       $    --     $    --      $    --
Issuance of common
stock to founders
for promissory
notes at $0.20 per
share.............          --      --   2,100,000     1        419       (420)          --          --           --
Issuance of Series
A convertible
preferred stock to
investors at $2.00
per share for
cash..............    2,790,000     --         --    --       5,580        --            --          --         5,580
Issuance of common
stock to employees
upon exercise of
stock options for
$0.20 per share...          --      --     100,000   --          20        --            --          --            20
Payments received
on promissory
notes.............          --      --         --    --         --         141           --          --           141
Deferred stock
compensation......          --      --         --    --       2,639        --         (2,639)        --           --
Amortization of
deferred stock
compensation......          --      --         --    --         --         --            863         --           863
Net loss from
inception to
December 31,
1997..............          --      --         --    --         --         --            --       (4,033)      (4,033)
                    -----------   ----  ---------- -----   --------    -------      --------    --------     --------
Balance at
December 31,
1997..............    2,790,000     --   7,660,000     1      8,658       (279)       (1,776)     (4,033)       2,571
Issuance of Series
A convertible
preferred stock to
investors at $2.00
per share for
cash..............        5,000     --         --    --          10        --            --          --            10
Issuance of Series
B convertible
preferred stock to
investors at $3.00
per share for
cash, less
issuance cost of
$36...............    3,666,667      1         --    --      10,966        --            --          --        10,967
Issuance of Series
C convertible
preferred stock to
a collaborator for
cash at $5.00 per
share.............    1,000,000     --         --    --       5,000        --            --          --         5,000
Options granted to
consultants for
services
rendered..........          --      --         --    --         209        --            --          --           209
Issuance of common
stock to
consultants for
cash and services
at $2.25 and $4.00
per share, and to
employees upon
exercise of stock
options for cash
and promissory
notes at $0.20 and
$0.30 per share...          --      --   1,570,500   --         477       (269)          --          --           208
Deferred stock
compensation......          --      --         --    --       2,386        --         (2,386)        --           --
Amortization of
deferred stock
compensation......          --      --         --    --         --         --          1,561         --         1,561
Net loss..........          --      --         --    --         --         --            --       (8,826)      (8,826)
                    -----------   ----  ---------- -----   --------    -------      --------    --------     --------
Balance at
December 31,
1998..............    7,461,667      1   9,230,500     1     27,706       (548)       (2,601)    (12,859)      11,700
Issuance of common
stock to employees
upon exercise of
options for cash
and promissory
notes at $0.20,
$0.30, $0.75 and
$7.50 per share...          --      --   2,640,650   --       1,645       (863)          --          --           782
Options granted to
consultants for
services
rendered..........          --      --         --    --         875        --            --          --           875
Issuance of common
stock for services
rendered and
certain technology
rights at $4.00,
$5.16 and $6.25
per share.........          --      --     191,600   --         845        --            --          --           845
Issuance of Series
D convertible
preferred stock to
investors at $5.50
per share for
cash, less
issuance costs of
$37...............    3,636,364     --         --    --      19,963        --            --          --        19,963
Issuance of Series
E convertible
preferred stock to
a collaborator at
$6.25 per share...      800,000     --         --    --       5,000        --            --          --         5,000
Issuance of common
stock for initial
public offering at
$16.00 per share
less issuance
costs of $9,403...          --     --    6,900,000     1    100,996        --            --          --       100,997
Conversion of
convertible
preferred stock to
common stock......  (11,898,031)    (1) 11,898,031     1        --         --            --          --           --
Deferred stock
compensation......          --      --         --    --      19,487        --        (19,487)        --           --
Amortization of
deferred stock
compensation......          --      --         --    --         --         --          4,872         --         4,872
Net loss..........          --      --         --    --         --         --            --      (11,318)     (11,318)
                    -----------   ----  ---------- -----   --------    -------      --------    --------     --------
Balance at
September 30,
1999..............          --    $ --  30,860,781 $   3   $176,517    $(1,411)     $(17,216)   $(24,177)    $133,716
                    ===========   ====  ========== =====   ========    =======      ========    ========     ========
</TABLE>

                            See accompanying notes.

                                      F-5
<PAGE>

                                 MAXYGEN, INC.

                            STATEMENTS OF CASH FLOWS
                     (in thousands, except per share data)

<TABLE>
<CAPTION>
                                                    Year ended December 31,
                                                    --------------------------
                                                     1997     1998      1999
                                                    -------  -------  --------
<S>                                                 <C>      <C>      <C>
Operating activities
Net loss........................................... $(4,033) $(8,826) $(11,318)
Adjustments to reconcile net loss to net cash used
 in operating activities:
  Depreciation and amortization....................      40      178       729
  Deferred stock compensation amortization.........     863    1,561     4,862
  Common stock issued and stock options granted to
   consultants for services rendered and for
   certain technology rights.......................     --       332     1,730
  Changes in operating assets and liabilities:
    Grant and other receivables....................     (10)    (590)   (2,438)
    Prepaid expenses and other current assets......     (32)    (239)     (529)
    Deposits and other assets......................     --      (422)     (211)
    Accounts payable...............................     101      365       (96)
    Accrued liabilities............................     231      208     1,757
    Deferred revenue...............................     199    4,691     2,572
    Related party payables.........................      52       53      (105)
                                                    -------  -------  --------
Net cash used in operating activities..............  (2,589)  (2,689)   (3,047)
                                                    -------  -------  --------

Investing activities
Acquisition of property and equipment..............    (459)    (760)   (4,492)
                                                    -------  -------  --------
Financing activities
Proceeds from issuance of convertible preferred
 stock, net of issuance costs......................   5,580   14,477    24,963
Proceeds from notes payable........................     --     1,500       --
Borrowings under equipment financing obligations...     --       --      1,834
Payments received on promissory notes..............     141      --        --
Proceeds from issuance of common stock, net of
 issuance costs....................................      20       85   101,779
                                                    -------  -------  --------
Net cash provided by financing activities..........   5,741   16,062   128,576
                                                    -------  -------  --------
Net increase in cash and cash equivalents..........   2,693   12,613   121,037
Cash and cash equivalents at beginning of period...     --     2,693    15,306
                                                    -------  -------  --------
Cash and cash equivalents at end of period.........  $2,693  $15,306  $136,343
                                                    =======  =======  ========
Schedule of noncash transactions
Issuance of common stock in exchange for note
 receivable........................................    $420     $269      $863
Conversion of note payable to preferred stock......   $ --    $1,500     $ --
</TABLE>

                              See accompanying notes.

                                      F-6
<PAGE>

                                 MAXYGEN, INC.

                         NOTES TO FINANCIAL STATEMENTS

1. Organization and Summary of Significant Accounting Policies

    Maxygen, Inc. (the "Company") was incorporated in Delaware on May 7, 1996
to develop and apply proprietary directed molecular evolution technologies,
also known as "MolecularBreeding," to evolve new or improved properties into
single genes, multigene pathways, vectors, and genomes. Since the technology
can be applied to a wide range of genetic targets, the Company will explore
commercial opportunities for the directed evolution of novel enzymes and
metabolic processes, novel products for agriculture, as well as opportunities
in the fields of human medicine, such as gene therapy, vaccines, and protein
pharmaceuticals.

    The MolecularBreeding directed molecular evolution technologies were
conceived at Affymax Research Institute ("Affymax"), a subsidiary of Glaxo
Group Ltd. In March 1997, as a result of the determination that a substantial
future investment in the further research and development of the technology was
merited, all rights to the MolecularBreeding directed molecular evolution
technologies were transferred by Affymax to the Company in exchange for the
issuance of 5,460,000 shares of common stock. This transaction represented the
formation of the Company and thus the common shares issued were not assigned
any value for accounting purposes. The technology rights transferred to the
Company represented research and development stage technology with no immediate
commercial application or alternative future use, and were recorded at the
historic carrying value of Glaxo Group Ltd. as determined in accordance with
generally accepted accounting principles in the United States. The total amount
of costs incurred by Glaxo Group Ltd. to develop the MolecularBreeding directed
molecular evolution technologies are not determinable but were not significant
to Affymax or Glaxo Group Ltd.

    Operations commenced in March 1997 and have consisted primarily of
technology and product development. Operational activity and expenses incurred
for the period from inception (May 7, 1996) through March 1997 were immaterial.

    Through December 31, 1998, the Company was in the development stage. During
fiscal 1999, the Company entered into its second corporate research
collaboration and recognized significant revenues associated with collaborative
research agreements and expects to receive significant revenues under these
agreements in the future. Consequently, the Company is no longer considered to
be in the development stage. The Company will require additional financial
resources to complete the development and commercialization of its products.
Management plans to continue to finance the Company primarily through issuances
of equity securities, collaborative research and development arrangements,
government grants, and debt financing. If the financing arrangements
contemplated by management are not consummated, the Company may have to seek
other sources of capital or reevaluate its operating plans.

Use of Estimates

    The preparation of financial statements in conformity with generally
accepted accounting principles requires management to make estimates and
assumptions that affect the reported amounts reported in the financial
statements and accompanying notes. Actual results could differ from those
estimates.

Cash and Cash Equivalents

    The Company considers all highly liquid investments purchased with original
maturities of three months or less to be cash equivalents. The Company's cash
and cash equivalents are maintained with one financial institution and consist
of depository accounts, master notes, and liquidity optimized general
investment contracts.

    The Company has classified its marketable securities as "available-for-
sale" and recorded these securities at fair value. At December 31, 1998 and
1999, these instruments are classified as cash

                                      F-7
<PAGE>

                                 MAXYGEN, INC.

                   NOTES TO FINANCIAL STATEMENTS--(Continued)

equivalents. Unrealized gains and losses, which are considered to be temporary,
are recorded as a separate component of stockholders' equity until realized. At
December 31, 1998 and 1999, the fair value of all of the Company's marketable
securities approximated cost.

Property and Equipment

    Property and equipment, including the cost of purchased software, are
stated at cost, less accumulated depreciation. Depreciation is provided using
the straight-line method over the estimated useful life of the assets
(generally three to five years). Leasehold improvements are amortized over the
shorter of six years or the estimated useful life of the assets.

Revenue Recognition

    Non-refundable up-front payments received in connection with research and
development collaboration agreements, including technology advancement funding
that is intended for the development of the Company's core technology, are
deferred and recognized on a straight-line basis over the relevant periods
specified in the agreement, generally the research term.

    Revenue related to collaborative research with the Company's corporate
collaborators is recognized as research services are performed over the related
funding periods for each contract. Under these agreements, the Company is
required to perform research and development activities as specified in each
respective agreement. The payments received under each respective agreement are
not refundable and are generally based on a contractual cost per full-time
equivalent employee working on the project. Research and development expenses
under the collaborative research agreements approximate or exceed the revenue
recognized under such agreements over the term of the respective agreements.
Deferred revenue may result when the Company does not incur the required level
of effort during a specific period in comparison to funds received under the
respective contracts. Milestone and royalty payments, if any, will be
recognized pursuant to collaborative agreements upon the achievement of
specified milestones.

    The Company was awarded Defense Advanced Research Projects Agency grants
and National Institute of Standards and Technology-Advanced Technology Program
grants totaling approximately $10.6 million in 1998 and $14.5 million in 1999,
for various research and development projects. The terms of these grant
agreements are three years. Revenue related to grant agreements is recognized
as related research and development expenses are incurred.

Research and Development Expenses

    Research and development expenses consist of costs incurred for Company-
sponsored as well as collaborative research and development activities. These
costs include direct and research-related overhead expenses as well as the cost
of funding research at universities and other research institutions, and are
expensed as incurred. Costs to acquire technologies that are utilized in
research and development and that have no alternative future use are expensed
when incurred (see Note 3).

Stock-Based Compensation

    The Company accounts for common stock options granted to employees using
the intrinsic value method and, thus, recognizes no compensation expense for
options granted with exercise

                                      F-8
<PAGE>

                                 MAXYGEN, INC.

                   NOTES TO FINANCIAL STATEMENTS--(Continued)

    prices equal to or greater than the fair value of the Company's common
stock on the date of the grant. In 1998 and 1999, the Company recognized
deferred stock compensation related to certain stock option grants (see Note
8). Pro forma information required by Statement of Financial Accounting
Standards No. 123, "Accounting for Stock-Based Compensation" ("SFAS 123") is
also included in Note 8.

    Stock compensation expense for options granted to nonemployees has been
determined in accordance with SFAS 123 and EITF 96-18 as the fair value of the
consideration received or the fair value of the equity instruments issued,
whichever is more reliably measured. The fair value of options granted to
nonemployees is periodically remeasured as the underlying options vest.

Net Loss Per Share

    Basic and diluted net loss per common share are presented in conformity
with the Statement of Financial Accounting Standards No. 128, "Earnings per
Share" ("SFAS 128"), for all periods presented. Following the guidance given by
the Securities and Exchange Commission Staff Accounting Bulletin No. 98, common
stock and convertible preferred stock that has been issued or granted for
nominal consideration prior to the anticipated effective date of the initial
public offering must be included in the calculation of basic and diluted net
loss per common share as if these shares had been outstanding for all periods
presented. To date, the Company has not issued or granted shares for nominal
consideration.

    In accordance with SFAS 128, basic and diluted net loss per share has been
computed using the weighted-average number of shares of common stock
outstanding during the period, less shares subject to repurchase. Pro forma
basic and diluted net loss per common share, as presented in the statements of
operations, has been computed for the years ended December 31, 1998 and 1999 as
described above, and also gives effect to the conversion of the convertible
preferred stock that automatically converted to common stock immediately prior
to the completion of the Company's initial public offering (using the if-
converted method) from the original date of issuance.

    The following table presents the calculation of basic, diluted and pro
forma basic and diluted net loss per share (in thousands, except per share
data):

<TABLE>
<CAPTION>
                                                    Year ended December 31,
                                                    --------------------------
                                                     1997     1998      1999
                                                    -------  -------  --------
<S>                                                 <C>      <C>      <C>
Net loss attributable to common stockholders....... $(4,033) $(8,826) $(13,518)
                                                    =======  =======  ========
Basic and diluted:
  Weighted-average shares of common stock
   outstanding.....................................   6,329    8,789    10,879
  Less: weighted-average shares subject to
   repurchase......................................  (1,412)  (2,041)   (2,025)
                                                    -------  -------  --------
  Weighted-average shares used in computing basic
   and diluted net loss per share..................   4,917    6,748     8,854
                                                    =======  =======  ========
Basic and diluted net loss per share............... $ (0.82) $ (1.31) $  (1.53)
                                                    =======  =======  ========
Pro forma:
  Shares used above................................            6,748     8,854
  Pro forma adjustment to reflect weighted effect
   of conversion of convertible preferred stock
   (unaudited).....................................            5,014     9,395
                                                             -------  --------
  Shares used in computing pro forma basic and
   diluted net loss per share (unaudited)..........           11,762    18,249
                                                             =======  ========
  Pro forma basic and diluted net loss per share
   (unaudited).....................................          $ (0.75) $  (0.74)
                                                             =======  ========
</TABLE>

                                      F-9
<PAGE>

                                 MAXYGEN, INC.

                   NOTES TO FINANCIAL STATEMENTS--(Continued)


    The Company has excluded all convertible preferred stock, outstanding stock
options, and shares subject to repurchase from the calculation of diluted loss
per common share because all such securities are antidilutive for all
applicable periods presented. The total number of shares excluded from the
calculations of diluted net loss per share, prior to application of the
treasury stock method for options, was 6,232,000, 11,305,000 and 2,601,000 at
December 31, 1997, 1998 and 1999, respectively. Such securities, had they been
dilutive, would have been included in the computations of diluted net loss per
share along with restricted common stock subject to the Company's right of
repurchase. See Note 8 for further information on these securities.

Segment Reporting

    As of January 1, 1998, the Company adopted Statement of Financial
Accounting Standards No. 131, "Disclosure about Segments of an Enterprise and
Related Information" ("SFAS 131"). SFAS 131 establishes annual and interim
reporting standards for an enterprise's operating segments and related
disclosures about its products, services, geographic areas, and major
customers. The Company has determined that it operates in only one segment.
Accordingly, the adoption of this statement had no impact on the Company's
financial statements.

Effect of New Accounting Standards

    In June 1998, the Financial Accounting Standards Board issued Statement of
Financial Accounting Standard No. 133, "Accounting for Derivative Instruments
and Hedging Activities" ("SFAS 133"), which will be effective for the year
ending 2001. This statement establishes accounting and reporting standards
requiring that every derivative instrument, including certain derivative
instruments imbedded in other contracts, be recorded in the balance sheet as
either an asset or liability measured at its fair value. The statement also
requires that changes in the derivative's fair value be recognized in earnings
unless specific hedge accounting criteria are met. The Company believes the
adoption of SFAS 133 will not have a material effect on the financial
statements, since it currently does not hold derivative instruments or engage
in hedging activities.

    In March 1998, the American Institute of Certified Public Accountants
issued Statement of Position 98-1, "Accounting for the Costs of Computer
Software Developed or Obtained for Internal Use" ("SOP 98-1"). "SOP 98-1"
requires that entities capitalize certain costs related to internal-use
software once certain criteria have been met. The adoption of SOP 98-1, as
required in 1999, had no impact on the Company's financial statements for the
year ended December 31, 1999. The Company expenses as incurred the costs
associated with developing software for use in research and development
activities in accordance with Statement of Financial Accounting Standards No.
2, "Accounting for Research and Development Costs" and related interpretations.

    In December 1999, the Securities and Exchange Commission ("SEC") issued
Staff Accounting Bulletin No. 101 ("SAB 101"), "Revenue Recognition", which
provides guidance on the recognition, presentation and disclosure of revenue in
financial statements filed with the SEC. SAB 101 outlines the basic criteria
that must be met to recognize revenue and provides guidance for disclosures
related to revenue recognition policies. Management believes that the Company's
revenue recognition policy is in compliance with the provisions of SAB 101 and
that the impact of SAB 101 will have no material effect on the financial
position or results of operations of the Company.

                                      F-10
<PAGE>

                                 MAXYGEN, INC.

                   NOTES TO FINANCIAL STATEMENTS--(Continued)

2. Collaborative Agreements

 AstraZeneca

    In June 1999, the Company entered into a noncancelable (other than for
material breach), five-year collaborative research agreement with Zeneca
Limited, a wholly-owned subsidiary of AstraZeneca plc ("AstraZeneca") to
improve the yield and quality of several of AstraZeneca's strategic crops.
Pursuant to the agreement, AstraZeneca paid $2.5 million in technology
advancement funding. AstraZeneca will also provide research funding of $15
million over the research term for defined research programs covering specified
crops, potential milestone payments that could exceed $100 million as well as
royalties on future product sales, as defined in the agreement. On an annual
basis beginning in the second year of the agreement, AstraZeneca must either
pay $1 million in annual technology advancement funding or purchase $3 million
shares of the Company's stock at a 50% premium to the current fair value. If
AstraZeneca elects this option, then the resulting $1 million premium will be
accounted for as technology advancement funding. The technology advancement
funding is intended to fund the Company's continuing development of its core
MolecularBreeding directed molecular evolution technology. Because the
agreement does not specify a required level of effort or other specific
performance criteria, the funding is being recognized ratably over the five-
year term of the agreement.

    Revenue recognized under the collaborative research agreement with
AstraZeneca was $1.6 million (18% of total collaborative research and
development revenues) for the year ended December 31, 1999, consisting of
research funding earned of $896,000 technology advancement funding of $536,000
and licensing fees of $161,000.

    In August 1999, in conjunction with the agreement, AstraZeneca purchased
800,000 shares of Series E convertible preferred stock at $6.25 per share. The
Company recorded a deemed dividend of $2.2 million at the date of issuance. The
deemed dividend is further described in Note 8.

 DuPont/Pioneer Hi-Bred International, Inc.

    In December 1998, the Company entered into a five-year collaborative
research and license agreement with Pioneer Hi-Bred International, Inc., a
subsidiary of E.I. duPont de Nemours and Company ("DuPont/Pioneer Hi-Bred") to
utilize MolecularBreeding directed molecular evolution technologies to generate
novel gene products for use in the development of specific crop protection and
quantity grain traits in corn, soybeans, and certain other crops. Pursuant to
the agreement, DuPont/Pioneer Hi-Bred paid an up-front, nonrefundable license
fee of $2.5 million which is being recognized ratably over the research term
and agreed to provide nonrefundable research and development funding of up to
$20 million, potential milestone payments of up to $45 million and royalties on
future product sales, as defined in the agreement. The agreement also provides
for nonrefundable technology advancement payments of up to $7.5 million which
are being recognized ratably over the applicable research term. The agreement
may be terminated by DuPont/Pioneer Hi-Bred after three years upon six-months
notice, if a specified technological milestone has not been met.

    Revenue recognized under the collaborative research agreement with
DuPont/Pioneer Hi-Bred was $62,000 and $6.0 million for the years ended
December 31, 1998 and 1999, respectively (6% and 67%, respectively, of total
collaborative research and development revenues).

                                      F-11
<PAGE>

                                 MAXYGEN, INC.

                   NOTES TO FINANCIAL STATEMENTS--(Continued)


    In December 1998, in conjunction with the agreement, DuPont/Pioneer Hi-Bred
purchased 1,000,000 shares of Series C convertible preferred stock at $5.00 per
share which was the fair value of the preferred stock on the date of issuance.
Furthermore, in December 1999, DuPont/Pioneer Hi-Bred purchased 312,500 shares
of the Company's common stock at the initial public offering price of $16.00.

 DSM

    In March 1999, the Company entered into a three-year collaborative research
and license agreement with Gist-brocades N.V., a subsidiary of DSM N.V. ("DSM")
to utilize the Company's proprietary MolecularBreeding directed molecular
evolution technologies to develop certain novel enzymes involved in the
manufacture of certain classes of antibiotics. Under the terms of the
agreement, DSM will receive worldwide commercialization rights and the Company
will receive research payments of approximately $2.3 million over the three-
year term and may receive royalty payments in the future. Total revenue of
$596,000 was recognized for the year ended December 31, 1999 (7% of total
collaborative research and development revenue).

 Novo Nordisk A/S

    In September 1997, the Company entered into a five-year License and
Collaboration Agreement with Novo Nordisk A/S ("Novo Nordisk") to use
MolecularBreeding directed molecular evolution technologies to develop
products. The agreement provides for research and development funding as well
as royalty payments on future products to the Company upon the occurrence of
specified events as defined in the agreement.

    As set forth in the agreement, Novo Nordisk will fund up to $500,000 of
research funding under the development program on an annual basis. Total
revenue of $544,000 and $454,000 was recognized for the years ended December
31, 1998 and 1999, respectively (51% and 5%, respectively, of total
collaborative research and development revenue).

 Other Collaborations

    The Company has entered into corporate collaborations under which it has
completed all of its research obligations. Revenue recognized pursuant to these
agreements was $341,000, $461,000, and $252,000 for the years ended December
31, 1997, 1998 and 1999, respectively (100%, 43%, and 3%, respectively, of
total collaborative research and development revenue).

3. Sponsored License and Research Agreements

    The Company has entered into several research agreements to fund research
at universities and other organizations. These agreements are generally
cancelable by either party upon written notice and may be extended by mutual
consent of both parties. Research and development expenses are recognized as
the related services are performed, generally ratably over the period of the
service. Expenses under these agreements were approximately $254,000, $702,000,
and $1,122,000 for the years ended December 31, 1997, 1998 and 1999,
respectively.

    In addition, in 1999 the Company issued 175,000 shares of common stock with
a fair value of $783,000 to research institutions in exchange for technology
licenses. This amount is included in

                                      F-12
<PAGE>

                                 MAXYGEN, INC.

                   NOTES TO FINANCIAL STATEMENTS--(Continued)

research and development expense for year ended December 31, 1999 as the
related technology is in research and development and has no alternative future
uses.

4. Property and Equipment

    Property and equipment consisted of the following (in thousands):

<TABLE>
<CAPTION>
                                                              December 31,
                                                           --------------------
                                                           1997   1998    1999
                                                           ----  ------  ------
   <S>                                                     <C>   <C>     <C>
   Leasehold improvements................................. $--   $  --   $1,352
   Machinery and laboratory equipment.....................  406   1,123   3,719
   Computer equipment and software........................   36      68     266
   Furniture and fixtures.................................   16      28     374
                                                           ----  ------  ------
                                                            458   1,219   5,711
   Less accumulated depreciation and amortization.........  (39)   (218)   (947)
                                                           ----  ------  ------
   Property and equipment, net............................ $419  $1,001  $4,764
                                                           ====  ======  ======
</TABLE>

5. Equipment Financing

    In June 1999, the Company entered into an equipment financing agreement for
up to $2.0 million with a financing company. In July through December 1999, the
Company financed $1.8 million in equipment purchases structured as loans. The
equipment loans are to be repaid over 48 months at interest rates of 11.73% to
12.13% and are secured by the related equipment. During the first 6 months of
the loan terms, the payments consist of interest only. Accumulated amortization
of assets acquired pursuant to these obligations was approximately $226,000 at
December 31, 1999.

    At December 31, 1999, the Company's future minimum principal payments under
the equipment financing arrangements are as follows (in thousands):

<TABLE>
<CAPTION>
   Year ended
   December 31,
   ------------
   <S>                                                                    <C>
   2000.................................................................. $  173
   2001..................................................................    511
   2002..................................................................    575
   2003..................................................................    564
   2004..................................................................     11
                                                                          ------
                                                                          $1,834
                                                                          ======
</TABLE>

6. Commitments

Services and Facility Agreement

    In February 1997, the Company entered into a services and facility
agreement, which was amended in September 1998 and February 1999, with Affymax
Research Institute ("ARI"), a related party. Under the agreement, ARI provided
certain accounting, human resources, materials management, facility, safety,
library, and information technology services, as well as the use of designated
space in the ARI facility for specified periods. In exchange, the Company
agreed to pay ARI $417,000 for the period from February 1,

                                      F-13
<PAGE>

                                 MAXYGEN, INC.

                   NOTES TO FINANCIAL STATEMENTS--(Continued)

1997 to December 31, 1997, $667,000 for the period from January 1, 1998 to
December 31, 1998, and $135,000 for the period from January 1, 1999 to April 1,
1999. These expenses were determined by ARI based upon the relative percentage
of effort expended by ARI personnel on the Company's affairs and the relative
use of facilities and fixed assets of ARI. Management believes that the charges
from ARI were reasonable and would not have been materially different on a
stand-alone basis. In addition, ARI agreed to transfer title of fixed assets
with a carrying value of approximately $55,000 to the Company. At December 31,
1998, the Company paid ARI approximately $105,000 under this agreement. The
agreement expired in April 1999.

Consulting Agreement

    In September 1998, the Company entered into a consulting arrangement
whereby the Company is committed to pay to a consulting firm up to a specified
percentage, as outlined in the agreement, of funds received in connection with
certain of the Company's agricultural collaborative agreements. The term of the
payments owed pursuant to this agreement is five years, ending in fiscal year
2004. For the fiscal years ended December 31, 1998 and 1999, the Company
expensed $199,000 and $292,000, respectively, related to this agreement.

Facility Leases

    The Company leases facilities under an operating lease which commenced in
1999. The lease expires for specified facilities in 2002 and 2005. The lease
contains a renewal option on the facilities under the portion of the lease that
expires in 2002. This lease also includes scheduled rent increases. The
scheduled rent increases are recognized on a straight-line basis over the term
of the lease. Minimum annual rental commitments under operating leases are as
follows (in thousands):

<TABLE>
<CAPTION>
   Year ended
   December 31,
   ------------
   <S>                                                                    <C>
   2000.................................................................. $1,528
   2001..................................................................  1,451
   2002..................................................................  1,113
   2003..................................................................  1,019
   2004..................................................................  1,043
   Thereafter............................................................    173
                                                                          ------
                                                                          $6,327
                                                                          ======
</TABLE>

    Rent expense allocated from the services and facility agreement for the
years ended December 31, 1997, 1998 and 1999 was approximately $122,000,
$147,000 and $1,269,000, respectively.

7. Related Party Notes Receivable

    The Company issued full recourse loans to certain employees, of which
$620,000 and $1,561,000 was outstanding at December 31, 1998 and 1999,
respectively. These loans bear interest at rates ranging from 4.83% to 6.42%
with terms ranging from three to five years. One loan totaling $150,000 was for
the purchase of the employee's residence and is secured by a deed of trust on
the employee's residence and is classified on the balance sheet as other
assets. The remaining loans were for the purchase of the Company's common stock
and are classified in stockholders' equity.

                                      F-14
<PAGE>

                                 MAXYGEN, INC.

                   NOTES TO FINANCIAL STATEMENTS--(Continued)


8. Stockholders' Equity

Convertible Preferred Stock

    In connection with the terms of the collaboration agreement with
AstraZeneca, the Company issued Series E convertible preferred stock in August
1999 at $6.25 per share. At the date of issuance, the Company believed the per
share price of $6.25 represented the fair value of the preferred stock and was
in excess of the deemed fair value of its common stock. Subsequent to the
commencement of the Company's initial public offering process, the Company re-
evaluated the deemed fair market value of its common stock as of August 1999
and determined it to be $9.00 per share. Accordingly, the incremental fair
value is deemed to be the equivalent of a preferred stock dividend. The Company
recorded the deemed dividend at the date of issuance by offsetting charges and
credits to additional paid in capital of $2,200,000, without any effect on
total stockholders' equity. The amount increased the loss allocable to common
stockholders in the calculation of basic net loss per share for the year ended
December 31, 1999.

    In December 1999, the Company completed its initial public offering of
common stock under the Securities Act of 1933, in which $101.0 million in net
proceeds was realized (including net proceeds from a simultaneous private
placement and the exercise of the underwriter's over-allotment option). Upon
the completion of the initial public offering, all of the Series A, B, C, D,
and E preferred stock outstanding converted into 11,898,031 shares of common
stock.

    Also, concurrent with the close of the Company's initial public offering,
the Company's articles of incorporation were amended to authorize 5,000,000
shares of undesignated preferred stock, none of which are issued or
outstanding. The Company's board of directors is authorized to fix the
designation, powers, preferences, and rights of any such series. The Company's
articles of incorporation was also amended to increase the authorized number of
shares of common stock to 70,000,000 shares.

1997 Stock Option Plan

    In 1997, the Company authorized the 1997 Stock Option Plan (the "Plan")
under which the board of directors may issue incentive stock options to
employees, including officers and members of the board of directors who are
also employees, and nonqualified stock options to employees, officers,
directors, consultants, and advisors of the Company. Under the Plan, incentive
options to purchase the Company's common shares may be granted to employees at
prices not lower than fair value at the date of grant, as determined by the
board of directors. Nonstatutory options (options which do not qualify as
incentive options) may be granted to key employees, including directors and
consultants, at prices not lower than 85% of fair value at the date of grant
(110% in certain cases), as determined by the board of directors. Options have
a term of ten years. Certain options are immediately exercisable, at the
discretion of the board of directors. Shares issued pursuant to the exercise of
an unvested option are subject to the Company's right of repurchase which lapse
over periods specified by the board of directors, generally four years from the
date of grant. If not immediately exercisable, options generally vest over four
years (vesting at a rate of 25% at the end of each year). The stock option plan
provides for annual increases in the number of shares available for issuance on
the first day of each year, beginning January 1, 2001, equal to the lesser of
1,500,000 shares, 4% of the outstanding shares on the date of the annual
increase or an amount determined by the board of directors.

                                      F-15
<PAGE>

                                 MAXYGEN, INC.

                   NOTES TO FINANCIAL STATEMENTS--(Continued)


    Activity under the Plan is as follows:

<TABLE>
<CAPTION>
                                                         Options Outstanding
                                                      --------------------------
                                                                    Weighted-
                                                                     Average
                                            Shares    Number of   Exercise Price
                                          Available     Shares      Per Share
                                          ----------  ----------  --------------
   <S>                                    <C>         <C>         <C>
   Shares authorized.....................  2,140,000         --         --
   Options granted....................... (1,891,550)  1,891,550      $0.20
   Options exercised.....................        --     (100,000)     $0.20
                                          ----------  ----------
   Balance at December 31, 1997..........    248,450   1,791,550      $0.20
   Shares authorized.....................  3,860,000         --         --
   Options granted....................... (1,537,120)  1,537,120      $0.30
   Options exercised.....................        --   (1,495,500)     $0.22
   Options canceled......................     38,500     (38,500)     $0.24
                                          ----------  ----------
   Balance at December 31, 1998..........  2,609,830   1,794,670      $0.27
   Shares Authorized.....................  1,500,000         --         --
   Options granted....................... (2,986,830)  2,986,830      $3.25
   Options exercised.....................        --   (2,640,650)     $0.62
   Options canceled......................     64,488     (64,488)     $0.35
                                          ----------  ----------
   Balance at December 31, 1999..........  1,187,488   2,076,362      $4.11
                                          ==========  ==========
</TABLE>

    The options outstanding and exercisable at December 31, 1999 are as
follows:

<TABLE>
<CAPTION>
               Options Outstanding
           -------------------------------  Weighted-Average
           Exercise                            Remaining
            Price      Number Outstanding   Contractual Life   Vested Options
           --------    ------------------   ----------------   --------------
                                               (In years)
           <S>         <C>                  <C>                <C>
            $ 0.20                336,825         7.6                 177,374
            $ 0.30                345,000         8.7                  58,750
            $ 0.50                 73,750         9.1                  22,750
            $ 0.63                 18,500         9.4                      --
            $ 0.75                398,162         9.7                   8,229
            $ 7.50                683,125         9.9                  17,500
            $10.80                  2,500         9.9                   2,500
            $11.00                127,250         9.9                      --
            $16.00                 91,250         10.0                     --
                                ---------                             -------
                                2,076,362                             287,103
                                =========                             =======
</TABLE>

    The weighted-average fair value of options granted in fiscal 1997, 1998 and
1999 was $1.80, $2.13, and $10.02 respectively. At December 31, 1997, 1998 and
1999, 75,000, 1,064,250, and 2,692,718 shares of common stock issued upon the
exercise of options were subject to repurchase at a weighted-average price of
$0.20, $0.23, and $0.61, respectively.

                                      F-16
<PAGE>

                                 MAXYGEN, INC.

                   NOTES TO FINANCIAL STATEMENTS--(Continued)


    Pro forma net loss information is required to be disclosed by SFAS 123 and
has been determined as if the Company has accounted for its employee stock
options under the fair market value method of that statement. The fair value
for these options was estimated at the date of grant using the minimum value
method with the following weighted-average assumptions:

<TABLE>
<CAPTION>
                                              1997         1998         1999
                                          ------------ ------------ ------------
   <S>                                    <C>          <C>          <C>
   Expected dividend yield...............      0%           0%           0%
   Risk-free interest rate range......... 5.9% to 6.6% 4.4% to 5.6% 5.1% to 6.2%
   Expected life.........................   5 years      5 years      5 years
</TABLE>

    For periods following the Company's initial public offering, the Black
Scholes method will be used to calculate the fair value of options granted.
This method includes the above assumptions as well as the estimated volatility
of the Company's common stock.

    The full effect of SFAS 123 will not be fully reflected until fiscal 2002.

    For purposes of pro forma disclosures, the estimated fair value of the
options is amortized to expense over the options' vesting periods. The
Company's pro forma net loss information is as follows (in thousands, except
per share amounts):

<TABLE>
<CAPTION>
                                                          Year ended
                                                         December 31,
                                                   --------------------------
                                                    1997     1998      1999
                                                   -------  -------  --------
   <S>                                             <C>      <C>      <C>
   Net loss attributable to common stockholders--
    as reported..................................  $(4,033) $(8,826) $(13,518)
                                                   =======  =======  ========
   Net loss attributable to common stockholders--
    pro forma....................................  $(4,054) $(8,871) $(13,669)
                                                   =======  =======  ========
   Basic and diluted net loss per share--as
    reported.....................................  $ (0.82) $ (1.31) $  (1.53)
                                                   =======  =======  ========
   Basic and diluted net loss per share--pro
    forma........................................  $ (0.82) $ (1.31) $  (1.54)
                                                   =======  =======  ========
</TABLE>

    In March through December 1998, the Company granted 173,000 common stock
options, of which 86,500 were fully vested, to consultants for services
rendered. In addition, in September 1998, 75,000 shares of common stock were
issued to consultants for services at a deemed fair value of $2.25 per share.
Expense of $364,000 was recognized in 1998 related to these transactions.
During the year ended December 31, 1999, the Company issued 15,000 shares of
common stock for services rendered at a deemed fair market value of $4.00 per
share. Also during the year ended December 31, 1999, the Company granted 87,000
common stock options to consultants for services rendered. Expense of $928,000
was recognized in 1999 related to these transactions. Options granted to
consultants are periodically re-valued as they vest in accordance with SFAS 123
and EITF 96-18 using a Black-Scholes model and the following weighted-average
assumptions for 1999: estimated volatility of 0.7, risk-free interest rates of
4.4% to 6.2%, no dividend yield, and an expected life of the option equal to
the full term, generally ten years from the date of grant.

    During the years ended December 31, 1997, 1998 and 1999, in connection with
the grant of certain share options to employees, the Company recorded deferred
stock compensation of $2.6 million, $2.4 million and $19.5 million,
respectively, representing the difference between the exercise price and the
deemed fair value of the Company's common stock for financial reporting
purposes on the date such stock options were granted. Deferred compensation is
included as a reduction of stockholders' equity and is being amortized to
expense on a graded vesting method. During the years ended December 31, 1997,
1998 and 1999, the Company recorded amortization of deferred stock compensation
expense of approximately $863,000, $1.6 million and $4.9 million, respectively.

                                      F-17
<PAGE>

                                 MAXYGEN, INC.

                   NOTES TO FINANCIAL STATEMENTS--(Continued)

1999 Employee Stock Purchase Plan

    In September 1999, the Company's board of directors adopted the 1999
Employee Stock Purchase Plan (the "Purchase Plan"). A total of 400,000 shares
of the Company's common stock have been reserved for issuance under the
Purchase Plan. The Purchase Plan permits eligible employees to purchase common
stock at a discount, but only through payroll deductions, during defined
offering periods. The price at which stock is purchased under the Purchase Plan
is equal to 85% of the fair market value of the common stock on the first or
last day of the offering period, whichever is lower. The initial offering
period commenced on December 16, 1999. In addition, the Purchase Plan provides
for annual increases in the number of shares available for issuance under the
purchase plan on the first day of each year, beginning January 1, 2001, equal
to the lesser of 200,000 shares, 0.75% of the outstanding shares on the date of
the annual increase or such amount as may be determined by the board. No shares
have been issued to date under the Puchase Plan.

Nonemployee Directors Stock Option Plan

    In September 1999, the Company adopted the 1999 Nonemployee Directors Stock
Option Plan and reserved a total of 300,000 shares of common stock for issuance
thereunder. Each nonemployee director who becomes a director of the Company
will be automatically granted a nonstatutory stock option to purchase 20,000
shares of common stock on the date on which such person first becomes a
director. At each board meeting immediately following each annual stockholders
meeting beginning with the first board meeting after the 1999 Annual
Stockholders Meeting, each nonemployee director will automatically be granted a
nonstatutory option to purchase 5,000 shares of common stock. The exercise
price of options under the director plan will be equal to the fair market value
of the common stock on the date of grant. The maximum term of the options
granted under the director plan is ten years. Each initial grant under the
director plan will vest as to 25% of the shares subject to the option one year
after the date of grant and at a rate of 25% of the shares at the end of each
year. Each subsequent grant will vest in full one year after the date of grant.
The director plan will terminate in September 2009, unless terminated earlier
in accordance with the provisions of the director plan.

Common Stock

    The founders' shares issued in March 1997 are also subject to repurchase.
The repurchase right for these shares lapses at a rate of 25% on an annual
basis in four years. The holders of unvested shares have voting and other
rights identical to other common stockholders. At December 31, 1997, 1998 and
1999, 1,575,000, 1,050,000, and 525,000 shares, respectively, of common stock
at a weighted-average price of $0.20 per share were subject to repurchase.

    At December 31, 1999, the Company has reserved shares of common stock for
future issuance as follows:

<TABLE>
   <S>                                                                 <C>
   1999 Stock Purchase Plan...........................................   400,000
   1999 Nonemployee Directors Stock Option Plan.......................   300,000
   1997 Stock Option Plan............................................. 3,263,850
                                                                       ---------
                                                                       3,963,850
                                                                       =========
</TABLE>

                                      F-18
<PAGE>

                                 MAXYGEN, INC.

                   NOTES TO FINANCIAL STATEMENTS--(Continued)


9. Income Taxes

    At December 31, 1999, the Company had federal and state net operating loss
carryforwards of approximately $10.4 million and $7.3 million, respectively.
The Company also had federal and California research and development tax credit
carryforwards of approximately $400,000 and $300,000, respectively. The net
operating loss and credit carryforwards will expire at various dates beginning
in the year 2011 through 2019, if not utilized. The state of California net
operating losses will begin to expire in the year 2006.

    Utilization of the net operating losses and credits may be subject to a
substantial annual limitation due to the ownership change limitations provided
by the Internal Revenue Code of 1986 and similar state provisions. The annual
limitation may result in the expiration of net operating losses and credits
before utilization.

    Deferred income taxes reflect the net tax effects of temporary differences
between the carrying amounts of assets for financial reporting and the amount
used for income tax purposes. Significant components of the Company's deferred
tax assets for federal and state income taxes are as follows (in thousands):

<TABLE>
<CAPTION>
                                                                December 31,
                                                               ----------------
                                                                1998     1999
                                                               -------  -------
   <S>                                                         <C>      <C>
   Net operating loss carryforwards........................... $ 1,800  $ 4,000
   Research credits...........................................     400      700
   Capitalized research and development.......................     100      300
   Deferred revenue...........................................     900    1,000
   Other......................................................     200      100
                                                               -------  -------
   Total deferred tax assets..................................   3,400    6,100
   Valuation allowance........................................  (3,400)  (6,100)
                                                               -------  -------
   Net deferred tax assets.................................... $   --   $   --
                                                               =======  =======
</TABLE>

    Because of the Company's lack of earnings history, the deferred tax assets
have been fully offset by a valuation allowance. The valuation allowance
increased by $2.2 million and $2.7 million during the years ended December 31,
1998 and 1999, respectively.

10. Subsequent Event (unaudited)

 Technological Resources PTY Limited

    In January 2000, the Company entered into a three year collaborative
research and development agreement with Technological Resources PTY Limited, a
wholly owned subsidiary of Rio Tinto Limited ("TRPL"), to develop novel
enzymatic systems to increase the efficiency of carbon dioxide fixation.
Pursuant to the agreement, TRPL agreed to provide nonrefundable research and
development funding and technology advancement payments of up to $2.7 million,
as well as revenue sharing on certain commercialized products and processes.

                                      F-19
<PAGE>

                                  UNDERWRITING

    Maxygen and the underwriters for the offering named below have entered into
an underwriting agreement with respect to the shares being offered. Subject to
certain conditions, each underwriter has severally agreed to purchase the
number of shares indicated in the following table. Goldman, Sachs & Co.,
FleetBoston Robertson Stephens Inc., Credit Suisse First Boston Corporation and
Invemed Associates LLC are the representatives of the underwriters.

<TABLE>
<CAPTION>
                            Underwriters                        Number of Shares
                            ------------                        ----------------
     <S>                                                        <C>
     Goldman, Sachs & Co.......................................
     FleetBoston Robertson Stephens Inc........................
     Credit Suisse First Boston Corporation....................
     Invemed Associates LLC....................................
                                                                   ---------
       Total...................................................    1,500,000
                                                                   =========
</TABLE>

    If the underwriters sell more shares than the total number set forth in the
table above, the underwriters have an option to buy up to an additional 225,000
shares from Maxygen to cover such sales. They may exercise that option for 30
days. If any shares are purchased under this option, the underwriters will
severally purchase shares in approximately the same proportion as set forth in
the table above.

    The following table shows the per share and total underwriting discounts
and commissions to be paid to the underwriters by Maxygen. These amounts are
shown assuming both no exercise and full exercise of the underwriters' option
to purchase 225,000 additional shares.

<TABLE>
<CAPTION>
                                                                Paid by Maxygen
                                                                ---------------
                                                                  No      Full
                                                               Exercise Exercise
                                                               -------- --------
     <S>                                                       <C>      <C>
     Per Share................................................  $        $
     Total....................................................  $        $
</TABLE>

    Shares sold by the underwriters to the public will initially be offered at
the initial price to public set forth on the cover of this prospectus. Any
shares sold by the underwriters to securities dealers may be sold at a discount
of up to $   per share from the initial price to public. Any of these
securities dealers may resell any shares purchased from the underwriters to
other brokers or dealers at a discount of up to $   per share from the initial
price to public. If all the shares are not sold at the initial price to public,
the representatives may change the offering price and the other selling terms.

    Maxygen has agreed with the underwriters not to dispose of or hedge any of
its common stock or securities convertible into or exchangeable for shares of
common stock during the period from the date of this prospectus continuing
through the date 90 days after the date of this prospectus, except with the
prior written consent of Goldman, Sachs & Co. This restriction does not apply
to any existing employee benefit plans or securities issued in connection with
acquisition transactions, provided that the recipients of such securities agree
not to dispose of or hedge any of such securities for the same 90 day period.
See "Shares Eligible for Future Sale" for a discussion of transfer
restrictions.

    Certain persons associated with Invemed Associates LLC, one of the
underwriters, hold an aggregate of 114,497 shares of common stock, of which
73,590 shares were purchased in August 1998 for $3.00 per share and 40,907
shares were purchased in June 1999 for $5.50 per share. These associated
persons also hold a pecuniary interest in a small portion of the shares of
common stock held by Technogen Associates, L.P. by virtue of limited
partnership interests held by such associated persons in Technogen Associates.
In addition, Invemed Fund L.P., a fund for which Invemed Associates is the sole
general partner, purchased 363,636 shares of common stock in June 1999 for
$5.50 per share. By virtue of Invemed Associates' partnership interest in
Invemed Fund, together with its entitlement to a percentage

                                      U-1
<PAGE>

return on investments made by Invemed Fund once the investment has generated a
return of 20 percent, Invemed Associates received 200,477 shares of common
stock on December 29, 1999, the date Invemed Fund declared a distribution of
the common stock held by Invemed Fund. In addition, three entities affiliated
with Credit Suisse First Boston Corporation, one of the underwriters, are the
limited partners of the Invemed Fund. At the time of the December 29, 1999
distribution of the common stock from the Invemed Fund, these entities received
an aggregate of 163,159 shares of common stock.

    In connection with the offering, the underwriters may purchase and sell
shares of common stock in the open market. These transactions may include short
sales, stabilizing transactions and purchases to cover positions created by
short sales. Short sales involve the sale by the underwriters of a greater
number of shares than they are required to purchase in the offering.
Stabilizing transactions consist of bids or purchases made for the purpose of
preventing or retarding a decline in the market price of the common stock while
the offering is in progress.

    The underwriters may also impose a penalty bid. This occurs when a
particular underwriter repays to the underwriters a portion of the underwriting
discount received by it because the representatives have repurchased shares
sold by or for the account of such underwriter in stabilizing or short covering
transactions.

    These activities by the underwriters may stabilize, maintain or affect the
market price of the common stock. As a result, the price of the common stock
may be higher than the price that otherwise might exist in the open market. If
these activities are commenced, they may be discontinued by the underwriters at
any time. These transactions may be effected on The Nasdaq National Market, in
the over-the-counter market or otherwise.

    Maxygen will pay the expenses of the offering, excluding underwriting
discounts and commissions. The expenses of the offering are estimated to be
approximately $500,000.

    Maxygen has agreed to indemnify the several underwriters against certain
liabilities, including liabilities under the Securities Act of 1933.

                                      U-2
<PAGE>

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

   No dealer, salesperson or other person is authorized to give any
information or to represent anything not contained in this prospectus. You
must not rely on any unauthorized information or representations. This
prospectus is an offer to sell only the shares offered hereby, but only under
circumstances and in jurisdictions where it is lawful to do so. The
information contained in this prospectus is current only as of its date.

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

                               TABLE OF CONTENTS

<TABLE>
<CAPTION>
                                                                          Page
                                                                          ----
<S>                                                                       <C>
Prospectus Summary.......................................................   3
Risk Factors.............................................................   7
Forward-Looking Statements...............................................  18
Use of Proceeds..........................................................  18
Price Range of Common Stock..............................................  19
Dividend Policy..........................................................  19
Capitalization...........................................................  20
Dilution.................................................................  21
Selected Financial Data..................................................  22
Management's Discussion and Analysis of Financial Condition and Results
 of Operations...........................................................  23
Business.................................................................  28
Management...............................................................  45
Related Party Transactions...............................................  56
Principal Stockholders...................................................  59
Description of Capital Stock.............................................  61
Shares Eligible for Future Sale..........................................  63
Legal Matters............................................................  64
Experts..................................................................  64
Where You Can Find Additional Information................................  65
Index to Financial Statements............................................ F-1
Underwriting............................................................. U-1
</TABLE>

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

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

                               1,500,000 Shares

                                 Maxygen, Inc.

                                 Common Stock


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

                                [MAXYGEN LOGO]

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


                             Goldman, Sachs & Co.

                              Robertson Stephens

                          Credit Suisse First Boston

                              Invemed Associates

                      Representatives of the Underwriters


- -------------------------------------------------------------------------------
- -------------------------------------------------------------------------------
<PAGE>

                                    PART II

                     Information Not Required In Prospectus

Item 13. Other Expenses of Issuance and Distribution.

    The following table sets forth all expenses to be paid by Maxygen, other
than the underwriting discounts and commissions payable by Maxygen, in
connection with the sale of the common stock being registered. All amounts
shown are estimates except for the SEC registration fee, the NASD filing fee
and the Nasdaq National Market filing fee.

<TABLE>
<CAPTION>
                                                                        AMOUNT
                                                                        TO BE
                                                                         PAID
                                                                       --------
   <S>                                                                 <C>
   SEC registration fee............................................... $ 72,950
   NASD filing fee....................................................   28,133
   Nasdaq National Market filing fee..................................   17,250
   Blue sky qualification fees and expenses...........................    2,500
   Printing and engraving expenses....................................  150,000
   Legal fees and expenses............................................  120,000
   Accounting fees and expenses.......................................   75,000
   Transfer agent and registrar fees and expenses.....................    2,500
   Miscellaneous......................................................   31,667
                                                                       --------
     Total............................................................ $500,000
                                                                       ========
</TABLE>

Item 14. Indemnification of Directors and Officers.

    Section 145 of the Delaware General Corporation Law permits indemnification
of officers, directors and other corporate agents under certain circumstances
and subject to certain limitations. Our Certificate of Incorporation and Bylaws
provide that we will indemnify our directors, officers, employees and agents to
the full extent permitted by Delaware General Corporation Law, including in
circumstances in which indemnification is otherwise discretionary under
Delaware law. In addition, we intend to enter into indemnification agreements
with our directors and officers that require us, among other things, to
indemnify them against certain liabilities that may arise by reason of their
status or service (other than liabilities arising from willful misconduct of a
culpable nature). The indemnification provisions in our Certificate of
Incorporation and Bylaws and the indemnification agreement entered into between
us and our directors may be sufficiently broad to permit indemnification of our
officers and directors for liabilities (including reimbursement of expenses
incurred) arising under the Securities Act. We also maintain director and
officer liability insurance to insure our directors and officers against the
cost of defense, settlement or payment of a judgment under certain
circumstances. In addition, the underwriting agreement filed as Exhibit 1.1 to
this Registration Statement provides for indemnification by the underwriters of
the Company and our officers and directors for certain liabilities arising
under the Securities Act, or otherwise. Reference is made to Item 17 of this
Registration Statement for additional information regarding indemnification of
officers and directors.

Item 15. Recent Sales of Unregistered Securities.

    Since our incorporation in May 1996, we have sold and issued the following
securities which were not registered under the Securities Act:

1. In March 1997, we issued to Affymax Technologies, N.V. and Glaxo Group
Limited (both subsidiaries of Glaxo Wellcome plc) a total of 5,460,000 shares
of common stock in exchange for the transfer of intellectual property and other
technology assets. In addition, we sold an aggregate of 2,100,000 shares of
common stock to four founders of Maxygen for aggregate consideration of
$420,000 which was paid by

                                      II-1
<PAGE>

promissory note, secured by the common stock underlying the stock purchase. In
May 1998, we issued 125,000 shares of common stock to the California Institute
of Technology in exchange for the license of intellectual property. In
September 1998, we sold 75,000 shares of common stock to three of our
consultants for aggregate consideration of $22,500. In March 1999, we issued
15,000 shares of common stock to Cahan & Associates in consideration for
consulting services. In April 1999, we issued 50,000 shares of common stock to
the University of Washington in exchange for the license of intellectual
property. In December 1999, we issued 1,600 shares of common stock to one of
our consultants for aggregate consideration of $10,000.

2. In March 1997, we sold 2,500,000 shares of Series A preferred stock to two
investors for aggregate consideration of $5,000,000. In December 1997, we sold
290,000 shares of Series A preferred stock to 16 investors for aggregate
consideration of $580,000. In April 1998, we sold 5,000 shares of Series A
preferred stock to one investor for aggregate consideration of $10,000.

3. In August 1998, we sold 3,666,667 shares of Series B preferred stock to 63
investors for aggregate consideration of $10,966,000.

4. In December 1998, we sold 1,000,000 shares of Series C preferred stock to
Pioneer Overseas Corporation for an aggregate consideration of $5,000,000.

5. In June 1999, we sold 3,636,364 shares of Series D preferred stock to 62
investors for aggregate consideration of $19,963,000.

6. In August 1999, we sold 800,000 shares of Series E preferred stock to
AstraZeneca Holdings, B.V. for aggregate consideration of $5,000,000.

7. From inception through December 22, 1999, we granted and outstanding
options to purchase an aggregate of 2,076,362 shares of common stock with
exercise prices ranging from $0.20 to $16.00 per share. From inception through
December 22, 1999, options to purchase 4,236,150 shares of common stock were
exercised for aggregate consideration of approximately $2 million.

   There were no underwriters employed in connection with any of the
transactions set forth in Item 15.

   The issuances of securities described in Items 15(1) through 15(6) were
deemed to be exempt from registration under the Securities Act in reliance on
Section 4(2) of the Securities Act and Regulation D promulgated thereunder as
transactions by an issuer not involving a public offering. With respect to the
grant of stock options described in Item 15(7), an exemption from registration
was unnecessary in that none of the transactions involved a "sale" of
securities as this term is used in Section 2(3) of the Securities Act. The
sale and issuance of securities and the exercise of options described in Item
15(7) were deemed to be exempt from registration under the Securities Act by
virtue of Rule 701 promulgated thereunder in that they were offered and sold
either pursuant to a written compensatory benefit plan or pursuant to a
written contract relating to compensation, as provided in Rule 701.The
recipients of securities in each such transaction represented their intention
to acquire the securities for investment only and not with a view to or for
sale in connection with any distribution thereof and appropriate legends were
affixed to the share certificates and other instruments issued in such
transactions. All recipients either received adequate information about us or
had access, through employment or other relationships, to such information.


                                     II-2
<PAGE>

Item 16. Exhibits and Financial Statement Schedules.

    (A) EXHIBITS

<TABLE>
<CAPTION>
 Exhibit
 Number                          Description of Document
 ------- ----------------------------------------------------------------------
 <C>     <S>
  1.1    Form of Underwriting Agreement
  3.1*   Amended and Restated Certificate of Incorporation (Filed as Exhibit
         3.8 to Amendment No. 1 to the Registration Statement on Form S-1
         (Registration No. 333-89413) on November 22, 1999 (the "November
         Amendment No. 1") and incorporated herein by reference)
  3.2*   Amended and Restated Bylaws (Filed as Exhibit 3.9 to the Registration
         Statement on Form S-1 (Registration No. 333-89413) on October 20, 1999
         (the "October Registration Statement") and incorporated herein by
         reference)
  4.1*   Specimen Common Stock Certificate (Filed as Exhibit 4.1 to the
         November Amendment No. 1 and incorporated herein by reference)
  4.2*   Registration Rights Agreement among Maxygen, Affymax Technologies
         N.V., Alejandro Zaffaroni and Glaxo Wellcome plc dated March 14, 1997
         (Filed as Exhibit 4.2 to the October Registration Statement and
         incorporated herein by reference)
  4.3*   Amendment to Registration Rights Agreement and Consent dated as of
         July 31, 1998 among Maxygen and certain holders of Series A preferred
         stock (Filed as Exhibit 4.3 to the October Registration Statement and
         incorporated herein by reference)
  4.4*   Second Amendment to Registration Rights Agreement and Consent dated as
         of December 23, 1998 among Maxygen and certain holders of Series A
         preferred stock and Series B preferred stock (Filed as Exhibit 4.4 to
         the October Registration Statement and incorporated herein by
         reference)
  4.5*   Third Amendment to Registration Rights Agreement and Consent dated as
         of June 15, 1999 among Maxygen, and certain holders of Series A
         preferred stock, Series B preferred stock, Series C preferred stock
         and Series D preferred stock (Filed as Exhibit 4.5 to the October
         Registration Statement and incorporated herein by reference)
  4.6*   Series E Preferred Stock Purchase Agreement among Maxygen, AstraZeneca
         Holdings, B.V. and Zeneca Limited dated as of June 18, 1999 (Filed as
         Exhibit 4.6 to the October Registration Statement and incorporated
         herein by reference)
  4.7*   Fourth Amendment to Registration Rights Agreement and Consent dated as
         of August 6, 1999 among Maxygen, certain holders of Series A preferred
         stock, Series B preferred stock, Series C preferred stock, Series D
         preferred stock and Series E preferred stock (Filed as Exhibit 4.7 to
         the October Registration Statement and incorporated herein by
         reference)
  5.1    Opinion of Heller Ehrman White & McAuliffe
 10.1*   1997 Stock Option Plan, as amended (Filed as Exhibit 10.1 to the
         November Amendment No. 1 and incorporated herein by reference)
 10.2*   Form of Promissory Note dated March 14, 1997 executed by each of
         Russell J. Howard, Isaac Stein and Willem P.C. Stemmer in favor of
         Maxygen (Filed as Exhibit 10.2 to the October Registration Statement
         and incorporated herein by reference)
 10.3*+  Technology Transfer Agreement among Maxygen, Affymax Technologies N.V.
         and Glaxo Wellcome plc dated March 14, 1997, as amended, effective
         March 1, 1998 (Filed as Exhibit 10.3 to Amendment No. 2 to the
         Registration Statement on Form S-1 (Registration No. 333-89413) on
         December 15, 1999 (the "December Amendment No. 2") and incorporated
         herein by reference)
 10.4*   Lease between Metropolitan Life Insurance Company and Maxygen dated
         October 21, 1998 (Filed as Exhibit 10.4 to the October Registration
         Statement and incorporated herein by reference)
 10.5*   First Amendment to Lease dated as of February 26, 1999 by and between
         Metropolitan Life Insurance Company and Maxygen (Filed as Exhibit 10.5
         to the October Registration Statement and incorporated herein by
         reference)
 10.6*   Promissory Note dated April 22, 1999 executed by Joseph Affholter and
         Roxanne Affholter in favor of Maxygen (Filed as Exhibit 10.6 to the
         October Registration Statement and incorporated herein by reference)
 10.7*   Form of Officer and Director Indemnification Agreement (Filed as
         Exhibit 10.7 to the October Registration Statement and incorporated
         herein by reference)
</TABLE>

                                      II-3
<PAGE>

<TABLE>
<CAPTION>
 Exhibit
 Number                          Description of Document
 ------- ----------------------------------------------------------------------
 <C>     <S>
 10.8*   1999 Nonemployee Directors Stock Option Plan (Filed as Exhibit 10.8 to
         the October Registration Statement and incorporated herein by
         reference)
 10.9*   1999 Employee Stock Purchase Plan (Filed as Exhibit 10.9 to the
         November Amendment No. 1 and incorporated herein by reference)
 10.10*  Form of Promissory Note issued in connection with exercise of stock
         options (Filed as Exhibit 10.10 to the October Registration Statement
         and incorporated herein by reference)
 10.11*+ License and Collaboration Agreement between Maxygen and Novo Nordisk
         A/S effective as of September 17, 1997, as amended June 29, 1998, July
         29, 1998, and April 19, 1999 (Filed as Exhibit 10.11 to the December
         Amendment No. 2 and incorporated herein by reference)
 10.12*+ Collaborative Research and License Agreement entered into as of
         December 23, 1998 by and between Pioneer Hi-Bred International, Inc.
         and Maxygen (Filed as Exhibit 10.12 to Post-Effective Amendment No. 1
         to the Registration Statement on Form S-1 (Registration No. 333-89413)
         on December 16, 1999 and incorporated herein by reference)
 10.13*+ Agreement between Maxygen and Gist-Brocades B.V. entered into March
         15, 1999 (Filed as Exhibit 10.13 to the December Amendment No. 2 and
         incorporated herein by reference)
 10.14*+ Collaboration Agreement effective as of June 18, 1999 by and between
         Zeneca Limited and Maxygen (Filed as Exhibit 10.14 to the December
         Amendment No. 2 and incorporated herein by reference)
 10.15++ Collaborative Research and Development Agreement made as of January
         19, 2000 between Technological Resources Pty Limited and Maxygen
 10.16   Letter agreement dated January 28, 2000, between Maxygen and Joseph A.
         Affholter
 10.17   Exclusive Consulting Agreement dated January 28, 2000, between Maxygen
         and Joseph A. Affholter
 10.18   Promissory Note dated January 28, 2000, executed by Joseph A.
         Affholter and Roxanne B. Affholter in favor of Maxygen
 10.19   Pledge Agreement dated January 28, 2000, among Joseph A. Affholter,
         Roxanne B. Affholter and Maxygen
 10.20++ Cooperative Research and Development Agreement between the National
         Cancer Institute, National Institutes of Health dated February 24,
         2000
 23.1    Consent of Ernst & Young LLP, Independent Auditors
 23.2    Consent of Heller Ehrman White & McAuliffe (included in Exhibit 5.1)
 24.1    Power of Attorney (see page II-6)
 27.1    Financial Data Schedule
</TABLE>
- --------
*   Previously filed in connection with the Registration Statement on Form S-1
    declared effective on December 15, 1999 and incorporated herein by
    reference.
+   Confidential treatment has been granted with respect to portions of the
    exhibit. A complete copy of the agreement, including the redacted terms,
    has been separately filed with the Securities and Exchange Commission.
++  Confidential treatment has been requested with respect to portions of the
    exhibit. A complete copy of the agreement including redacted terms, has
    been separately filed with the Securities and Exchange Commission.

    (B) FINANCIAL STATEMENT SCHEDULES.

    All schedules for which provision is made in the applicable accounting
regulations of the Securities and Exchange Commission are not required under
the related instructions or are inapplicable, and therefore have been omitted.

Item 17. Undertakings

    The undersigned Registrant hereby undertakes to provide to the underwriters
at the closing specified in the underwriting agreement, certificates in such
denominations and registered in such names as required by the underwriters to
permit prompt delivery to each purchaser.

                                      II-4
<PAGE>

   Insofar as indemnification by the Registrant for liabilities arising under
the Securities Act may be permitted to directors, officers and controlling
persons of the Registrant pursuant to the provisions

   Insofar as indemnification by the Registrant for liabilities arising under
the Securities Act may be permitted to directors, officers and controlling
persons of the Registrant pursuant to the provisions referenced in Item 14 of
this Registration Statement or otherwise, the Registrant has been advised that
in the opinion of the Commission such indemnification is against public policy
as expressed in the Securities referenced in Item 14 of this Registration
Statement or otherwise, the Registrant has been advised that in the opinion of
the Commission such indemnification is against public policy as expressed in
the Securities Act, and is, therefore, unenforceable. In the event that a
claim for indemnification against such liabilities (other than the payment by
the Registrant of expenses incurred or paid by a director, officer, or
controlling person of the Registrant in the successful defense of any action,
suit or proceeding) is asserted by such director, officer or controlling
person in connection with the securities being registered hereunder, the
Registrant will, unless in the opinion of its counsel the matter has been
settled by controlling precedent, submit to a court of appropriate
jurisdiction the question whether such indemnification by it is against public
policy as expressed in the Securities Act and will be governed by the final
adjudication of such issue.

   The undersigned registrant hereby undertakes that:

    (1) For purposes of determining any liability under the Securities Act,
  the information omitted from the form of prospectus filed as part of this
  Registration Statement in reliance upon Rule 430A and contained in a form
  of prospectus filed by the Registrant pursuant to Rule 424(b)(1) or (4) or
  497(h) under the Securities Act shall be deemed to be part of this
  Registration Statement as of the time it was declared effective; and

    (2) For the purpose of determining any liability under the Securities
  Act, each post-effective amendment that contains a form of prospectus shall
  be deemed to be a new registration statement relating to the securities
  offered therein, and the offering of such securities at the time shall be
  deemed to be the initial bona fide offering thereof.

                                     II-5
<PAGE>

                                   SIGNATURES

    Pursuant to the requirements of the Securities Act of 1933, the Registrant
has duly caused this Registration Statement to be signed on its behalf by the
undersigned, thereunto duly authorized, in Redwood City, California, on the 3rd
day of March, 2000.

                                        MAXYGEN, INC.

                                           /s/ Russell J. Howard
                                        By:_____________________________________
                                       Russell J. Howard, Ph.D.
                                     President and Chief Executive Officer

                               POWER OF ATTORNEY

    KNOW ALL PERSONS BY THESE POWER OF ATTORNEY PRESENTS, that each person
whose signature appears below hereby constitutes and appoints Isaac Stein and
Simba Gill, and each of them acting individually, as his or her true and lawful
attorneys-in-fact and agents, each with full power of substitution, for him or
her in any and all capacities, to sign any and all amendments to this
Registration Statement (including post-effective amendments or any abbreviated
registration statement and any amendments thereto filed pursuant to Rule 462(b)
increasing the number of securities for which registration is sought), and to
file the same, with exhibits thereto and other documents in connection
therewith, with the Securities and Exchange Commission, granting unto said
attorneys-in-fact and agents, with full power of each to act alone, full power
and authority to do and perform each and every act and thing requisite and
necessary to be done in connection therewith, as fully for all intents and
purposes as he or she might or could do in person, hereby ratifying and
confirming all that said attorneys-in-fact and agents, or his or their
substitute or substitutes, may lawfully do or cause to be done by virtue
hereof.

    Pursuant to the requirements of the Securities Act, this Registration
Statement has been signed by the following persons in the capacities and on the
dates indicated:

<TABLE>
<CAPTION>
              Signature                            Title                   Date
              ---------                            -----                   ----

 <C>                                  <S>                              <C>
 /s/ Russell J. Howard, Ph.D.         President, Chief Executive       March 3, 2000
 ____________________________________  Officer and Director
 Russell J. Howard, Ph.D.              (Principal Executive Officer)

 /s/ Simba Gill, Ph.D.                Senior Vice President of         March 3, 2000
 ____________________________________ Business Development and Chief
 Simba Gill, Ph.D.                    Financial Officer (Principal
                                      Financial and Accounting
                                      Officer)

 /s/ Isaac Stein                      Chairman of the Board            March 3, 2000
 ____________________________________
 Isaac Stein

 /s/ Robert J. Glaser, M.D.           Director                         March 3, 2000
 ____________________________________
 Robert J. Glaser, M.D.

 /s/ M.R.C. Greenwood, Ph.D.          Director                         March 3, 2000
 ____________________________________
 M.R.C. Greenwood, Ph.D.
</TABLE>

                                      II-6
<PAGE>

<TABLE>
<CAPTION>
              Signature                            Title                   Date
              ---------                            -----                   ----

 <C>                                  <S>                              <C>
 /s/ Adrian Hennah                    Director                         March 3, 2000
 ____________________________________
 Adrian Hennah

 /s/ Gordon Ringold, Ph.D.            Director                         March 3, 2000
 ____________________________________
 Gordon Ringold, Ph.D.

 /s/ George Poste, Ph.D.              Director                         March 3, 2000
 ____________________________________
 George Poste, Ph.D.
</TABLE>

                                      II-7
<PAGE>

                                 EXHIBIT INDEX

<TABLE>
<CAPTION>
 Exhibit
 Number                          Description of Document
 ------- ----------------------------------------------------------------------
 <C>     <S>
  1.1    Form of Underwriting Agreement
  3.1*   Amended and Restated Certificate of Incorporation (Filed as Exhibit
         3.8 to Amendment No. 1 to the Registration Statement on Form S-1
         (Registration No. 333-89413) on November 22, 1999 (the "November
         Amendment No. 1") and incorporated herein by reference)
  3.2*   Amended and Restated Bylaws (Filed as Exhibit 3.9 to the Registration
         Statement on Form S-1 (Registration No. 333-89413) on October 20, 1999
         (the "October Registration Statement") and incorporated herein by
         reference)
  4.1*   Specimen Common Stock Certificate (Filed as Exhibit 4.1 to the
         November Amendment No. 1 and incorporated herein by reference)
  4.2*   Registration Rights Agreement among Maxygen, Affymax Technologies
         N.V., Alejandro Zaffaroni and Glaxo Wellcome plc dated March 14, 1997
         (Filed as Exhibit 4.2 to the October Registration Statement and
         incorporated herein by reference)
  4.3*   Amendment to Registration Rights Agreement and Consent dated as of
         July 31, 1998 among Maxygen and certain holders of Series A preferred
         stock (Filed as Exhibit 4.3 to the October Registration Statement and
         incorporated herein by reference)
  4.4*   Second Amendment to Registration Rights Agreement and Consent dated as
         of December 23, 1998 among Maxygen and certain holders of Series A
         preferred stock and Series B preferred stock (Filed as Exhibit 4.4 to
         the October Registration Statement and incorporated herein by
         reference)
  4.5*   Third Amendment to Registration Rights Agreement and Consent dated as
         of June 15, 1999 among Maxygen, and certain holders of Series A
         preferred stock, Series B preferred stock, Series C preferred stock
         and Series D preferred stock (Filed as Exhibit 4.5 to the October
         Registration Statement and incorporated herein by reference)
  4.6*   Series E Preferred Stock Purchase Agreement among Maxygen, AstraZeneca
         Holdings, B.V. and Zeneca Limited dated as of June 18, 1999 (Filed as
         Exhibit 4.6 to the October Registration Statement and incorporated
         herein by reference)
  4.7*   Fourth Amendment to Registration Rights Agreement and Consent dated as
         of August 6, 1999 among Maxygen, certain holders of Series A preferred
         stock, Series B preferred stock, Series C preferred stock, Series D
         preferred stock and Series E preferred stock (Filed as Exhibit 4.7 to
         the October Registration Statement and incorporated herein by
         reference)
  5.1    Opinion of Heller Ehrman White & McAuliffe
 10.1*   1997 Stock Option Plan, as amended (Filed as Exhibit 10.1 to the
         November Amendment No. 1 and incorporated herein by reference)
 10.2*   Form of Promissory Note dated March 14, 1997 executed by each of
         Russell J. Howard, Isaac Stein and Willem P.C. Stemmer in favor of
         Maxygen (Filed as Exhibit 10.2 to the October Registration Statement
         and incorporated herein by reference)
 10.3*+  Technology Transfer Agreement among Maxygen, Affymax Technologies N.V.
         and Glaxo Wellcome plc dated March 14, 1997, as amended, effective
         March 1, 1998 (Filed as Exhibit 10.3 to Amendment No. 2 to the
         Registration Statement on Form S-1 (Registration No. 333-89413) on
         December 15, 1999 (the "December Amendment No. 2") and incorporated
         herein by reference)
 10.4*   Lease between Metropolitan Life Insurance Company and Maxygen dated
         October 21, 1998 (Filed as Exhibit 10.4 to the October Registration
         Statement and incorporated herein by reference)
 10.5*   First Amendment to Lease dated as of February 26, 1999 by and between
         Metropolitan Life Insurance Company and Maxygen (Filed as Exhibit 10.5
         to the October Registration Statement and incorporated herein by
         reference)
 10.6*   Promissory Note dated April 22, 1999 executed by Joseph Affholter and
         Roxanne Affholter in favor of Maxygen (Filed as Exhibit 10.6 to the
         October Registration Statement and incorporated herein by reference)
 10.7*   Form of Officer and Director Indemnification Agreement (Filed as
         Exhibit 10.7 to the October Registration Statement and incorporated
         herein by reference)
</TABLE>
<PAGE>

<TABLE>
<CAPTION>
 Exhibit
 Number                          Description of Document
 ------- ----------------------------------------------------------------------
 <C>     <S>
 10.8*   1999 Nonemployee Directors Stock Option Plan (Filed as Exhibit 10.8 to
         the October Registration Statement and incorporated herein by
         reference)
 10.9*   1999 Employee Stock Purchase Plan (Filed as Exhibit 10.9 to the
         November Amendment No. 1 and incorporated herein by reference)
 10.10*  Form of Promissory Note issued in connection with exercise of stock
         options (Filed as Exhibit 10.10 to the October Registration Statement
         and incorporated herein by reference)
 10.11*+ License and Collaboration Agreement between Maxygen and Novo Nordisk
         A/S effective as of September 17, 1997, as amended June 29, 1998, July
         29, 1998, and April 19, 1999 (Filed as Exhibit 10.11 to the December
         Amendment No. 2 and incorporated herein by reference)
 10.12*+ Collaborative Research and License Agreement entered into as of
         December 23, 1998 by and between Pioneer Hi-Bred International, Inc.
         and Maxygen (Filed as Exhibit 10.12 to Post-Effective Amendment No. 1
         to the Registration Statement on Form S-1 (Registration No. 333-89413)
         on December 16, 1999 and incorporated herein by reference)
 10.13*+ Agreement between Maxygen and Gist-Brocades B.V. entered into March
         15, 1999 (Filed as Exhibit 10.13 to the December Amendment No. 2 and
         incorporated herein by reference)
 10.14*+ Collaboration Agreement effective as of June 18, 1999 by and between
         Zeneca Limited and Maxygen (Filed as Exhibit 10.14 to the December
         Amendment No. 2 and incorporated herein by reference)
 10.15++ Collaborative Research and Development Agreement made as of January
         19, 2000 between Technological Resources Pty Limited and Maxygen
 10.16   Letter agreement dated January 28, 2000, between Maxygen and Joseph A.
         Affholter
 10.17   Exclusive Consulting Agreement dated January 28, 2000, between Maxygen
         and Joseph A. Affholter
 10.18   Promissory Note dated January 28, 2000, executed by Joseph A.
         Affholter and Roxanne B. Affholter in favor of Maxygen
 10.19   Pledge Agreement dated January 28, 2000, among Joseph A. Affholter,
         Roxanne B. Affholter and Maxygen
 10.20++ Cooperative Research and Development Agreement between the National
         Cancer Institute, National Institutes of Health dated February 24,
         2000
 23.1    Consent of Ernst & Young LLP, Independent Auditors
 23.2    Consent of Heller Ehrman White & McAuliffe (included in Exhibit 5.1)
 24.1    Power of Attorney (see page II-6)
 27.1    Financial Data Schedule
</TABLE>
- --------
*   Previously filed in connection with the Registration Statement on Form S-1
    declared effective on December 15, 1999 and incorporated herein by
    reference.
+   Confidential treatment has been granted with respect to portions of the
    exhibit. A complete copy of the agreement, including the redacted terms,
    has been separately filed with the Securities and Exchange Commission.
++  Confidential treatment has been requested with respect to portions of the
    exhibit. A complete copy of the agreement including redacted terms, has
    been separately filed with the Securities and Exchange Commission.

<PAGE>

                                                                     EXHIBIT 1.1

                                 Maxygen, Inc.

                                 Common Stock

                          par value $0.0001 per share

                            Underwriting Agreement
                            ----------------------

                                                                          , 2000


Goldman, Sachs & Co.,
Credit Suisse First Boston Corporation,
FleetBoston Robertson Stephens Inc.,
Invemed Associates LLC,
 As representatives of the several Underwriters
  named in Schedule I hereto,
c/o Goldman, Sachs & Co.
85 Broad Street,
New York, New York 10004.

Ladies and Gentlemen:

  Maxygen, Inc., a Delaware corporation (the "Company"), proposes, subject to
the terms and conditions stated herein, to issue and sell to the Underwriters
named in Schedule I hereto (the "Underwriters") an aggregate of 1,500,000
shares (the "Firm Shares") and, at the election of the Underwriters, up to
225,000 additional shares (the "Optional Shares") of Common Stock, par
value $.0001 ("Stock") of the Company (the Firm Shares and the Optional Shares
that the Underwriters elect to purchase pursuant to Section 2 hereof being
collectively called the "Shares").

  1.      The Company represents and warrants to, and agrees with, each of the
Underwriters that:

  (a)     A registration statement on Form S-1 (File No. 333-[_____]) (the
"Initial Registration Statement") in respect of the Shares has been filed with
the Securities and Exchange Commission (the "Commission"); the Initial
Registration Statement and any post-effective amendment thereto, each in the
form heretofore delivered to you, and, excluding exhibits thereto, to you for
each of the other Underwriters, have been declared effective by the Commission
in such form; other than a registration statement, if any, increasing the size
of the offering (a "Rule 462(b) Registration Statement"), filed pursuant to Rule
462(b) under the Securities Act of 1933, as amended (the "Act"), which became
effective upon filing, no other document with respect to the Initial
Registration Statement has heretofore been filed with the Commission; and no
stop order suspending the effectiveness of the Initial Registration Statement,
any post-effective amendment thereto or the Rule 462(b) Registration Statement,
if any, has been issued and no proceeding for that purpose has been
<PAGE>

initiated or threatened by the Commission (any preliminary prospectus included
in the Initial Registration Statement or filed with the Commission pursuant to
Rule 424(a) of the rules and regulations of the Commission under the Act is
hereinafter called a "Preliminary Prospectus"; the various parts of the Initial
Registration Statement and the Rule 462(b) Registration Statement, if any,
including all exhibits thereto and including the information contained in the
form of final prospectus filed with the Commission pursuant to Rule 424(b) under
the Act in accordance with Section 5(a) hereof and deemed by virtue of Rule 430A
under the Act to be part of the Initial Registration Statement at the time it
was declared effective, each as amended at the time such part of the Initial
Registration Statement became effective or such part of the Rule 462(b)
Registration Statement, if any, became or hereafter becomes effective, are
hereinafter collectively called the "Registration Statement"; such final
prospectus, in the form first filed pursuant to Rule 424(b) under the Act, is
hereinafter called the "Prospectus";

  (b)     No order preventing or suspending the use of any Preliminary
Prospectus has been issued by the Commission, and each Preliminary Prospectus,
at the time of filing thereof, conformed in all material respects to the
requirements of the Act and the rules and regulations of the Commission
thereunder, and did not contain an untrue statement of a material fact or omit
to state a material fact required to be stated therein or necessary to make the
statements therein, in the light of the circumstances under which they were
made, not misleading; provided, however, that this representation and warranty
shall not apply to any statements or omissions made in reliance upon and in
conformity with information furnished in writing to the Company by an
Underwriter through Goldman, Sachs & Co. expressly for use therein;

  (c)     The Registration Statement conforms, and the Prospectus and any
further amendments or supplements to the Registration Statement or the
Prospectus will conform, in all material respects to the requirements of the Act
and the rules and regulations of the Commission thereunder and do not and will
not, as of the applicable effective date as to the Registration Statement and
any amendment thereto, and as of the applicable filing date as to the Prospectus
and any amendment or supplement thereto, contain an untrue statement of a
material fact or omit to state a material fact required to be stated therein or
necessary to make the statements therein not misleading; provided, however, that
this representation and warranty shall not apply to any statements or omissions
made in reliance upon and in conformity with information furnished in writing to
the Company by an Underwriter through Goldman, Sachs & Co. expressly for use
therein;

  (d)     Neither the Company nor any of its subsidiaries has sustained since
the date of the latest audited financial statements included in the Prospectus
any material loss or interference with its business from fire, explosion, flood
or other calamity, whether or not covered by insurance, or from any labor
dispute or court or governmental action, order or decree, otherwise than as set
forth or contemplated in the Prospectus; and, since the respective dates as of
which information is given in the Registration Statement and the Prospectus,
there has not been any change in the capital stock (other than upon the exercise
of options granted pursuant to employee or director stock option plans) or long-
term debt of the Company or any of its subsidiaries or any material adverse
change, or any development involving a prospective material adverse change, in
or affecting the general affairs, management, financial position, stockholders'
equity or results of operations of the Company and its subsidiaries, otherwise
than as set forth or contemplated in the Prospectus;

                                       2
<PAGE>

  (e) The Company and its subsidiaries have good and marketable title in fee
simple to all real property and good and marketable title to all personal
property owned by them, in each case free and clear of all liens, encumbrances
and defects except such as are described in the Prospectus or such as do not
materially affect the value of such property and do not materially interfere
with the use made and proposed to be made of such property by the Company and
its subsidiaries; and any real property and buildings held under lease by the
Company and its subsidiaries are held by them under valid, subsisting and
enforceable leases with such exceptions as are not material and do not interfere
with the use made and proposed to be made of such property and buildings by the
Company and its subsidiaries;

  (f) The Company has been duly incorporated and is validly existing as a
corporation in good standing under the laws of Delaware, with power and
authority (corporate and other) to own its properties and conduct its business
as described in the Prospectus, and has been duly qualified as a foreign
corporation for the transaction of business and is in good standing under the
laws of each other jurisdiction in which it owns or leases properties or
conducts any business so as to require such qualification, or is subject to no
material liability or disability by reason of the failure to be so qualified in
any such jurisdiction; and each subsidiary of the Company has been duly
incorporated and is validly existing as a corporation in good standing under the
laws of its jurisdiction of incorporation;

  (g) The Company has an authorized capitalization as set forth in the
Prospectus, and all of the issued shares of capital stock of the Company have
been duly and validly authorized and issued, are fully paid and non-assessable
and conform to the description of the Stock contained in the Prospectus; and all
of the issued shares of capital stock of each subsidiary of the Company have
been duly and validly authorized and issued, are fully paid and non-assessable
and (except for directors' qualifying shares) are owned directly or indirectly
by the Company, free and clear of all liens, encumbrances, equities or claims;

  (h) The unissued Shares to be issued and sold by the Company to the
Underwriters hereunder have been duly and validly authorized and, when issued
and delivered against payment therefor as provided herein, will be duly and
validly issued and fully paid and non-assessable and will conform to the
description of the Stock contained in the Prospectus;

  (i) The issue and sale of the Shares by the Company and the compliance by the
Company with all of the provisions of this Agreement and the consummation of the
transactions herein contemplated will not conflict with or result in a breach or
violation of any of the terms or provisions of, or constitute a default under,
any indenture, mortgage, deed of trust, loan agreement or other material
agreement or material instrument to which the Company or any of its subsidiaries
is a party or by which the Company or any of its subsidiaries is bound or to
which any of the property or assets of the Company or any of its subsidiaries is
subject, nor will such action result in any violation of the provisions of the
Certificate of Incorporation or By-laws of the Company or any statute or any
order, rule or regulation of any court or governmental agency or body having
jurisdiction over the Company or any of its subsidiaries or any of their
properties; and no consent, approval, authorization, order, registration or
qualification of or with any such court or governmental agency or body is
required for the issue and sale of the Shares or the consummation by the Company
of the transactions contemplated by this Agreement, except the registration
under the Act of the Shares and such consents, approvals, authorizations,
registrations or qualifications as may be required under state

                                       3
<PAGE>

securities or Blue Sky laws in connection with the purchase and distribution of
the Shares by the Underwriters;

  (j) Neither the Company nor any of its subsidiaries is in violation of its
Certificate of Incorporation or By-laws or in default in the performance or
observance of any material obligation, agreement, covenant or condition
contained in any indenture, mortgage, deed of trust, loan agreement, lease or
other agreement or instrument to which it is a party or by which it or any of
its properties may be bound;

  (k) The statements set forth in the Prospectus under the caption "Description
of Capital Stock", insofar as they purport to constitute a summary of the terms
of the Stock and under the caption "Underwriting", insofar as they purport to
describe the provisions of the laws and documents referred to therein, are
accurate, complete and fair;

  (l) Other than as set forth in the Prospectus, there are no legal or
governmental proceedings pending to which the Company or any of its subsidiaries
is a party or of which any property of the Company or any of its subsidiaries is
the subject which, if determined adversely to the Company or any of its
subsidiaries, would individually or in the aggregate have a material adverse
effect on the current or future consolidated financial position, stockholders'
equity or results of operations of the Company and its subsidiaries; and, to the
best of the Company's knowledge, no such proceedings are threatened or
contemplated by governmental authorities or threatened by others;

  (m) The Company is not and, after giving effect to the offering and sale of
the Shares, will not be an "investment company", as such term is defined in the
Investment Company Act of 1940, as amended (the "Investment Company Act");

  (n) Neither the Company nor any of its affiliates does business with the
government of Cuba or with any person or affiliate located in Cuba within the
meaning of Section 517.075, Florida Statutes;

  (o) Ernst & Young, LLP, who have certified certain financial statements of the
Company and its subsidiaries, are independent public accountants as required by
the Act and the rules and regulations of the Commission thereunder; and

  (p) All of the stockholders listed on Schedule II hereto have delivered
agreements (collectively, the "Lock-up Agreements") that restrict the holders
thereof from, among other things, selling, granting any option for the purchase
of, pledging, or otherwise transferring or disposing of the economic interest
in, any shares of Stock held by such persons, or any securities convertible into
or exercisable or exchangeable for Stock, for a period of 90 days after the date
of the Prospectus without the prior written consent of Goldman, Sachs & Co.,
provided, however, that any shares of Stock purchased by the persons listed in
Schedule II-A hereto in the Company's initial public offering or traded in the
Nasdaq National Market or any other over-the-counter market or stock exchange
are not subject to the foregoing restriction; and the Company has no reason to
believe any Lock-up Agreement is not a valid and binding obligation of each
party thereto other than the Underwriters; and

                                       4
<PAGE>

  (q) The Company has imposed a stop-transfer instruction with the Company's
transfer agent in order to enforce the Lock-up Agreements.

  (r) The Company has reviewed its operations and that of its subsidiaries and
any third parties with which the Company or any of its subsidiaries has a
material relationship to evaluate the extent to which the business or operations
of the Company or any of its subsidiaries has been and  will be affected by the
Year 2000 Problem.  As a result of such review, the Company has no reason to
believe, and does not believe, that the Year 2000 Problem has had or will have a
material adverse effect on the general affairs, management, the current or
future consolidated financial position, business prospects, stockholders' equity
or results of operations of the Company and its subsidiaries or result in any
material loss or interference with the Company's business or operations.  The
"Year 2000 Problem" as used herein means any significant risk that computer
hardware or software used in the receipt, transmission, processing,
manipulation, storage, retrieval, retransmission or other utilization of data or
in the operation of mechanical or electrical systems of any kind will not, in
the case of dates or time periods occurring after December 31, 1999, function at
least as effectively as in the case of dates or time periods occurring prior to
January 1, 2000.

  2. Subject to the terms and conditions herein set forth, (a) the Company
agrees to issue and sell to each of the Underwriters, and each of the
Underwriters agrees, severally and not jointly, to purchase from the Company, at
a purchase price per share of $[___], the number of Firm Shares set forth
opposite the name of such Underwriter in Schedule I hereto and (b) in the event
and to the extent that the Underwriters shall exercise the election to purchase
Optional Shares as provided below, the Company agrees to issue and sell to each
of the Underwriters, and each of the Underwriters agrees, severally and not
jointly, to purchase from the Company, at the purchase price per share set forth
in clause (a) of this Section 2, that portion of the number of Optional Shares
as to which such election shall have been exercised (to be adjusted by you so as
to eliminate fractional shares) determined by multiplying such number of
Optional Shares by a fraction, the numerator of which is the maximum number of
Optional Shares which such Underwriter is entitled to purchase as set forth
opposite the name of such Underwriter in Schedule I hereto and the denominator
of which is the maximum number of Optional Shares that all of the Underwriters
are entitled to purchase hereunder.

  The Company hereby grants to the Underwriters the right to purchase at their
election up to 225,000 Optional Shares, at the purchase price per share set
forth in the paragraph above, for the sole purpose of covering sales of shares
in excess of the number of Firm Shares.  Any such election to purchase Optional
Shares may be exercised only by written notice from you to the Company, given
within a period of 30 calendar days after the date of this Agreement, setting
forth the aggregate number of Optional Shares to be purchased and the date on
which such Optional Shares are to be delivered, as determined by you but in no
event earlier than the First Time of Delivery (as defined in Section 4 hereof)
or, unless you and the Company otherwise agree in writing, earlier than two or
later than ten business days after the date of such notice.

  3. Upon the authorization by you of the release of the Firm Shares, the
several Underwriters propose to offer the Firm Shares for sale upon the terms
and conditions set forth in the Prospectus.

                                       5
<PAGE>

  4.  (a) The Shares to be purchased by each Underwriter hereunder, in
definitive form, and in such authorized denominations and registered in such
names as Goldman, Sachs & Co. may request upon at least forty-eight hours' prior
notice to the Company shall be delivered by or on behalf of the Company to
Goldman, Sachs & Co., through the facilities of the Depository Trust Company
("DTC"), for the account of such Underwriter, against payment by or on behalf of
such Underwriter of the purchase price therefor by wire transfer of Federal
(same-day) funds to the account specified by the Company to Goldman, Sachs & Co.
at least forty-eight hours in advance. The Company will cause the certificates
representing the Shares to be made available for checking and packaging at least
twenty-four hours prior to the Time of Delivery (as defined below) with respect
thereto at the office of DTC or its designated custodian (the "Designated
Office"). The time and date of such delivery and payment shall be, with respect
to the Firm Shares, 9:30 a.m., New York City time, on [________] or such other
time and date as Goldman, Sachs & Co. and the Company may agree upon in writing,
and, with respect to the Optional Shares, 9:30 a.m., New York time, on the date
specified by Goldman, Sachs & Co. in the written notice given by Goldman, Sachs
& Co. of the Underwriters' election to purchase such Optional Shares, or such
other time and date as Goldman, Sachs & Co. and the Company may agree upon in
writing. Such time and date for delivery of the Firm Shares is herein called the
"First Time of Delivery", such time and date for delivery of the Optional
Shares, if not the First Time of Delivery, is herein called the "Second Time of
Delivery", and each such time and date for delivery is herein called a "Time of
Delivery".

  (b) The documents to be delivered at each Time of Delivery by or on behalf of
the parties hereto pursuant to Section 7 hereof, including the cross receipt for
the Shares and any additional documents requested by the Underwriters pursuant
to Section 7(j) hereof, will be delivered at the offices of Heller Ehrman White
& McAuliffe, 2500 Sand Hill Road, Menlo Park, California, 94025-7063 (the
"Closing Location"), and the Shares will be delivered at the Designated Office,
all at such Time of Delivery.  A meeting will be held at the Closing Location at
1:00 p.m., New York City time, on the New York Business Day next preceding such
Time of Delivery, at which meeting the final drafts of the documents to be
delivered pursuant to the preceding sentence will be available for review by the
parties hereto.  For the purposes of this Section 4, "New York Business Day"
shall mean each Monday, Tuesday, Wednesday, Thursday and Friday which is not a
day on which banking institutions in New York are generally authorized or
obligated by law or executive order to close.

  5.  The Company agrees with each of the Underwriters:

  (a) To prepare the Prospectus in a form approved by you and to file such
Prospectus pursuant to Rule 424(b) under the Act not later than the Commission's
close of business on the second business day following the execution and
delivery of this Agreement, or, if applicable, such earlier time as may be
required by Rule 430A(a)(3) under the Act; to make no further amendment or any
supplement to the Registration Statement or Prospectus which shall be
disapproved by you promptly after reasonable notice thereof; to advise you,
promptly after it receives notice thereof, of the time when any amendment to the
Registration Statement has been filed or becomes effective or any supplement to
the Prospectus or any amended Prospectus has been filed and to furnish you with
copies thereof; to advise you, promptly after it receives notice thereof, of the
issuance by the Commission of any stop order or of any order preventing or
suspending the use of any Preliminary Prospectus or prospectus, of the
suspension of the qualification of the Shares for offering or sale in any
jurisdiction, of the initiation or threatening of any proceeding for any such
purpose, or of any

                                       6
<PAGE>

request by the Commission for the amending or supplementing of the Registration
Statement or Prospectus or for additional information; and, in the event of the
issuance of any stop order or of any order preventing or suspending the use of
any Preliminary Prospectus or prospectus or suspending any such qualification,
promptly to use its best efforts to obtain the withdrawal of such order;

  (b) Promptly from time to time to take such action as you may reasonably
request to qualify the Shares for offering and sale under the securities laws of
such jurisdictions as you may request and to comply with such laws so as to
permit the continuance of sales and dealings therein in such jurisdictions for
as long as may be necessary to complete the distribution of the Shares, provided
that in connection therewith the Company shall not be required to qualify as a
foreign corporation or to file a general consent to service of process in any
jurisdiction;

  (c) Prior to 10:00 A.M., New York City time, on the New York Business Day next
succeeding the date of this Agreement and from time to time, to furnish the
Underwriters with copies of the Prospectus in New York City in such quantities
as you may reasonably request, and, if the delivery of a prospectus is required
at any time prior to the expiration of nine months after the time of issue of
the Prospectus in connection with the offering or sale of the Shares and if at
such time any event shall have occurred as a result of which the Prospectus as
then amended or supplemented would include an untrue statement of a material
fact or omit to state any material fact necessary in order to make the
statements therein, in the light of the circumstances under which they were made
when such Prospectus is delivered, not misleading, or, if for any other reason
it shall be necessary during such period to amend or supplement the Prospectus
in order to comply with the Act, to notify you and upon your request to prepare
and furnish without charge to each Underwriter and to any dealer in securities
as many copies as you may from time to time reasonably request of an amended
Prospectus or a supplement to the Prospectus which will correct such statement
or omission or effect such compliance, and in case any Underwriter is required
to deliver a prospectus in connection with sales of any of the Shares at any
time nine months or more after the time of issue of the Prospectus, upon your
request but at the expense of such Underwriter, to prepare and deliver to such
Underwriter as many copies as you may request of an amended or supplemented
Prospectus complying with Section 10(a)(3) of the Act;

  (d) To make generally available to its securityholders as soon as practicable,
but in any event not later than eighteen months after the effective date of the
Registration Statement (as defined in Rule 158(c) under the Act), an earnings
statement of the Company and its subsidiaries (which need not be audited)
complying with Section 11(a) of the Act and the rules and regulations thereunder
(including, at the option of the Company, Rule 158);

  (e) During the period beginning from the date hereof and continuing to and
including the date 90 days after the date of the Prospectus, not to offer, sell,
contract to sell or otherwise dispose of, except as provided hereunder any
securities of the Company that are substantially similar to the Shares,
including but not limited to any securities that are convertible into or
exchangeable for, or that represent the right to receive, Stock or any such
substantially similar securities (other than pursuant to employee, director or
consultant stock option or stock purchase plans existing on, or upon the
conversion or exchange of convertible or exchangeable securities outstanding as
of, the date of this Agreement or in connection with any acquisition
transaction, provided that the recipients of the Company's securities in any
such transaction agree in writing not to offer, sell, contract to sell or
otherwise dispose of such securities during the same 90 day period), without
your prior written consent;

                                       7
<PAGE>

  (f) To furnish to its stockholders as soon as practicable after the end of
each fiscal year an annual report (including a balance sheet and statements of
income, stockholders' equity and cash flows of the Company and its consolidated
subsidiaries certified by independent public accountants) and, as soon as
practicable after the end of each of the first three quarters of each fiscal
year (beginning with the fiscal quarter ending after the effective date of the
Registration Statement), to make available to its stockholders consolidated
summary financial information of the Company and its subsidiaries for such
quarter in reasonable detail;

  (g) During a period of five years from the effective date of the Registration
Statement, to furnish to you copies of all reports or other communications
(financial or other) furnished to stockholders, and to deliver to you (i) as
soon as they are available, copies of any reports and financial statements
furnished to or filed with the Commission or any national securities exchange on
which any class of securities of the Company is listed; and (ii) such additional
information concerning the business and financial condition of the Company as
you may from time to time reasonably request (such financial statements to be on
a consolidated basis to the extent the accounts of the Company and its
subsidiaries are consolidated in reports furnished to its stockholders generally
or to the Commission);

  (h) To use the net proceeds received by it from the sale of the Shares
pursuant to this Agreement in the manner specified in the Prospectus under the
caption "Use of Proceeds";

  (i) To use its best efforts to list for quotation the Shares on the National
Association of Securities Dealers Automated Quotations National Market System
("NASDAQ");

  (j) To file with the Commission such information on Form 10-Q or Form 10-K as
may be required by Rule 463 under the Act;

  (k) If the Company elects to rely upon Rule 462(b), the Company shall file a
Rule 462(b) Registration Statement with the Commission in compliance with Rule
462(b) by 10:00 P.M., Washington, D.C. time, on the date of this Agreement, and
the Company shall at the time of filing either pay to the Commission the filing
fee for the Rule 462(b) Registration Statement or give irrevocable instructions
for the payment of such fee pursuant to Rule 111(b) under the Act; and

  (l) The Company will (i) cooperate with the Underwriters to enforce the terms
of each Lock-up Agreement (as defined in Section 1(p)), (ii) issue stop-transfer
instructions to the transfer agent for the Stock with respect to any transaction
or contemplated transaction that would constitute a breach of or default under
the applicable Lock-up Agreement, and (iii) upon written request of Goldman,
Sachs & Co., release from the Lock-up Agreements those shares of Stock held by
those holders set forth in such request. In addition, except with the prior
written consent of Goldman, Sachs & Co., the Company agrees not to amend or
terminate, waive any right under, or consent to any transaction that would
otherwise be prohibited under, any Lock-up Agreement, or take any other action
that would directly or indirectly have the same effect as such an amendment,
termination, waiver or consent; and

  6.  The Company covenants and agrees with the several Underwriters that the
Company will pay or cause to be paid the following: (i) the fees, disbursements
and expenses of the Company's counsel and accountants in connection with the
registration of the Shares under the Act and all other expenses in connection
with the preparation, printing and filing of the Registration Statement, any
Preliminary Prospectus and the Prospectus and amendments and supplements thereto
and the mailing and delivering of copies thereof to the Underwriters and
dealers; (ii) the cost of printing or producing any Agreement among
Underwriters, this Agreement, the Blue Sky Memorandum, closing

                                       8
<PAGE>

documents (including any compilations thereof) and any other documents in
connection with the offering, purchase, sale and delivery of the Shares; (iii)
all expenses in connection with the qualification of the Shares for offering and
sale under state securities laws as provided in Section 5(b) hereof, including
the fees and disbursements of counsel for the Underwriters in connection with
such qualification and in connection with the Blue Sky survey (iv) all fees and
expenses in connection with listing the Shares on the NASDAQ; (v) the filing
fees incident to, and the fees and disbursements of counsel for the Underwriters
in connection with, securing any required review by the National Association of
Securities Dealers, Inc. of the terms of the sale of the Shares; (vi) the cost
of preparing stock certificates; (vii) the cost and charges of any transfer
agent or registrar; and (viii) all other costs and expenses incident to the
performance of its obligations hereunder which are not otherwise specifically
provided for in this Section. It is understood, however, that, except as
provided in this Section, and Sections 8 and 11 hereof, the Underwriters will
pay all of their own costs and expenses, including the fees of their counsel,
stock transfer taxes on resale of any of the Shares by them, and any advertising
expenses connected with any offers they may make.

  7.  The obligations of the Underwriters hereunder, as to the Shares to be
delivered at each Time of Delivery, shall be subject, in their discretion, to
the condition that all representations and warranties and other statements of
the Company herein are, at and as of such Time of Delivery, true and correct,
the condition that the Company shall have performed all of its obligations
hereunder theretofore to be performed, and the following additional conditions:

  (a) The Prospectus shall have been filed with the Commission pursuant to Rule
424(b) within the applicable time period prescribed for such filing by the rules
and regulations under the Act and in accordance with Section 5(a) hereof; if the
Company has elected to rely upon Rule 462(b), the Rule 462(b) Registration
Statement shall have become effective by 10:00 P.M., Washington, D.C. time, on
the date of this Agreement; no stop order suspending the effectiveness of the
Registration Statement or any part thereof shall have been issued and no
proceeding for that purpose shall have been initiated or threatened by the
Commission; and all requests for additional information on the part of the
Commission shall have been complied with to your reasonable satisfaction;

  (b) Wilson Sonsini Goodrich & Rosati, Professional Corporation, counsel for
the Underwriters, shall have furnished to you such written opinion or opinions
(a draft of each such opinion is attached as Annex II(a) hereto), dated such
Time of Delivery, with respect to the matters covered in paragraphs (i), (ii),
(vii),  (xiii) and (xiv) of subsection (c) below as well as such other related
matters as you may reasonably request, and such counsel shall have received such
papers and information as they may reasonably request to enable them to pass
upon such matters;

  (c) Heller, Ehrman White & McAuliffe, counsel for the Company, shall have
furnished to you their written opinion (a draft of such opinion is attached as
Annex II(b) hereto), dated such Time of Delivery, in form and substance
satisfactory to you, to the effect that:

      (i)    The Company has been duly incorporated and is validly existing as a
corporation in good standing under the laws of the Delaware with power and
authority (corporate and other) to own its properties and conduct its business
as described in the Prospectus;

      (ii)   The Company has an authorized capitalization as set forth in the
Prospectus, and all of the issued shares of capital stock of the Company
(including the Shares being delivered at such Time of Delivery) have been duly
and validly authorized and issued and are fully paid and non-assessable; and the
Shares conform to the description of the Stock contained in the Prospectus;

                                       9
<PAGE>

      (iii)  The Company has been duly qualified as a foreign corporation for
the transaction of business and is in good standing under the laws of each other
jurisdiction in which it owns or leases properties or conducts any business so
as to require such qualification or is subject to no material liability or
disability by reason of failure to be so qualified in any such jurisdiction
(such counsel being entitled to rely in respect of the opinion in this clause
upon opinions of local counsel, published compilations of the laws of such state
and in respect of matters of fact upon certificates of officers of the Company,
provided that such counsel shall state that they believe that both you and they
are justified in relying upon such opinions and certificates);

      (iv)   Each subsidiary of the Company has been duly incorporated and is
validly existing as a corporation in good standing under the laws of its
jurisdiction of incorporation; and all of the issued shares of capital stock of
each such subsidiary have been duly and validly authorized and issued, are fully
paid and non-assessable, and (except for directors' qualifying shares) are owned
directly or indirectly by the Company, free and clear of all liens,
encumbrances, equities or claims (such counsel being entitled to rely in respect
of the opinion in this clause upon opinions of local counsel and in respect to
matters of fact upon certificates of officers of the Company or its
subsidiaries, provided that such counsel shall state that they believe that both
you and they are justified in relying upon such opinions and certificates);

      (v)    The Company and its subsidiaries have good and marketable title in
fee simple to all real property owned by them, in each case free and clear of
all liens, encumbrances and defects except such as (a) are described in the
Prospectus or (b) do not materially affect the value of such property and do not
interfere with the use made and proposed to be made of such property by the
Company and its subsidiaries in a manner that could reasonably be expected to
result in a material adverse change, in the condition, financial or otherwise,
or in the earnings, business, operations or prospects, whether or not arising
from transactions in the ordinary course of business, of the Company and its
subsidiaries, considered as one entity. Any real property and buildings held
under lease by the Company and its subsidiaries are held by them under valid,
subsisting and enforceable leases with such exceptions as are not material and
do not interfere with the use made and proposed to be made of such property and
buildings by the Company and its subsidiaries (in giving the opinion in this
clause, such counsel may state that no examination of record titles for the
purpose of such opinion has been made, and that they are relying upon a general
review of the titles of the Company and its subsidiaries, upon opinions of local
counsel and abstracts, reports and policies of title companies rendered or
issued at or subsequent to the time of acquisition of such property by the
Company or its subsidiaries, upon opinions of counsel to the lessors of such
property and, in respect to matters of fact, upon certificates of officers of
the Company or its subsidiaries, provided that such counsel shall state that
they believe that both you and they are justified in relying upon such opinions,
abstracts, reports, policies and certificates);

      (vi)   To such counsel's knowledge and other than as set forth in the
Prospectus, there are no legal or governmental proceedings pending to which the
Company or any of its subsidiaries is a party or of which any property of the
Company or any of its subsidiaries is the subject and, to such counsel's
knowledge, no such proceedings are threatened or contemplated by governmental
authorities or threatened by others;

      (vii)  This Agreement has been duly authorized, executed and delivered by
the Company;

                                       10
<PAGE>

     (viii)  The issue and sale of the Shares being delivered at such Time of
Delivery by the Company and the compliance by the Company with all of the
provisions of this Agreement and the consummation of the transactions herein
contemplated will not conflict with or result in a breach or violation of any of
the terms or provisions of, or constitute a default under, any indenture,
mortgage, deed of trust, loan agreement or other agreement or instrument known
to such counsel to which the Company or any of its subsidiaries is a party or by
which the Company or any of its subsidiaries is bound or to which any of the
property or assets of the Company or any of its subsidiaries is subject, nor
will such action result in any violation of the provisions of the Certificate of
Incorporation or By-laws of the Company or any statute or any order, rule or
regulation known to such counsel of any court or governmental agency or body
having jurisdiction over the Company or any of its subsidiaries or any of their
properties;

     (ix)    No consent, approval, authorization, order, registration or
qualification of or with any such court or governmental agency or body is
required for the issue and sale of the Shares or the consummation by the Company
of the transactions contemplated by this Agreement, except the registration
under the Act of the Shares, and such consents, approvals, authorizations,
registrations or qualifications as may be required under state securities or
Blue Sky laws in connection with the purchase and distribution of the Shares by
the Underwriters;

     (x)     Neither the Company nor any of its subsidiaries is in violation of
its Certificate of Incorporation or By-laws or in default in the performance or
observance of any material obligation, agreement, covenant or condition
contained in any indenture, mortgage, deed of trust, loan agreement, lease or
other agreement or instrument to which it is a party or by which it or any of
its properties may be bound;

     (xi)    The statements set forth in the Prospectus under the caption
"Description of Capital Stock", insofar as they purport to constitute a summary
of the terms of the Stock are accurate, complete and fair;

     (xii)   The Company is not an "investment company", as such term is defined
in the Investment Company Act; and

     (xiii)  The Registration Statement and the Prospectus and any further
amendments and supplements thereto made by the Company prior to such Time of
Delivery (other than the financial statements and related schedules therein, as
to which such counsel need express no opinion) comply as to form in all material
respects with the requirements of the Act and the rules and regulations
thereunder.

     (xiv)   Although they do not assume any responsibility for the accuracy,
completeness or fairness of the statements contained in the Registration
Statement or the Prospectus, except for those referred to in the opinion in
subsection (xi) of this section 7(c), they have no reason to believe that, as of
its effective date, the Registration Statement or any further amendment thereto
made by the Company prior to such Time of Delivery (other than the financial
statements and related schedules therein, as to which such counsel need express
no opinion) contained an untrue statement of a material fact or omitted to state
a material fact required to be stated therein or necessary to make the
statements therein not misleading or that, as of its date, the Prospectus or any
further amendment or supplement thereto made by the Company prior to such Time
of Delivery (other than the financial statements and related schedules therein,
as to which such counsel need express no opinion) contained an untrue statement
of a material fact or omitted to state a material fact necessary

                                       11
<PAGE>

to make the statements therein, in the light of the circumstances under which
they were made, not misleading or that, as of such Time of Delivery, either the
Registration Statement or the Prospectus or any further amendment or supplement
thereto made by the Company prior to such Time of Delivery (other than the
financial statements and related schedules therein, as to which such counsel
need express no opinion) contains an untrue statement of a material fact or
omits to state a material fact necessary to make the statements therein, in the
light of the circumstances under which they were made, not misleading; and they
do not know of any amendment to the Registration Statement required to be filed
or of any contracts or other documents of a character required to be filed as an
exhibit to the Registration Statement or required to be described in the
Registration Statement or the Prospectus which are not filed or described as
required;

  (d) On the date of the Prospectus at a time prior to the execution of this
Agreement, at 9:30 a.m., New York City time, on the effective date of any post-
effective amendment to the Registration Statement filed subsequent to the date
of this Agreement and also at each Time of Delivery, Ernst & Young, LLP shall
have furnished to you a letter or letters, dated the respective dates of
delivery thereof, in form and substance satisfactory to you, to the effect set
forth in Annex I hereto (the executed copy of the letter delivered prior to the
execution of this Agreement is attached as Annex I(a) hereto and a draft of the
form of letter to be delivered on the effective date of any post-effective
amendment to the Registration Statement and as of each Time of Delivery is
attached as Annex I(b) hereto);

  (e) (i) Neither the Company nor any of its subsidiaries shall have sustained
since the date of the latest audited financial statements included in the
Prospectus any loss or interference with its business from fire, explosion,
flood or other calamity, whether or not covered by insurance, or from any labor
dispute or court or governmental action, order or decree, otherwise than as set
forth or contemplated in the Prospectus, and (ii) since the respective dates as
of which information is given in the Prospectus there shall not have been any
change in the capital stock or long-term debt of the Company or any of its
subsidiaries or any change, or any development involving a prospective change,
in or affecting the general affairs, management, financial position,
stockholders' equity or results of operations of the Company and its
subsidiaries, otherwise than as set forth or contemplated in the Prospectus, the
effect of which, in any such case described in clause (i) or (ii), is in the
judgment of the Representatives so material and adverse as to make it
impracticable or inadvisable to proceed with the public offering or the delivery
of the Shares being delivered at such Time of Delivery on the terms and in the
manner contemplated in the Prospectus;

  (f) On or after the date hereof (i) no downgrading shall have occurred in the
rating accorded the Company's debt securities, if any, or preferred stock, if
any, by any "nationally recognized statistical rating organization", as that
term is defined by the Commission for purposes of Rule 436(g)(2) under the Act,
and (ii) no such organization shall have publicly announced that it has under
surveillance or review, with possible negative implications, its rating of any
of the Company's debt securities or preferred stock;

  (g) On or after the date hereof there shall not have occurred any of the
following: (i) a suspension or material limitation in trading in securities
generally on the New York Stock Exchange or on NASDAQ; (ii) a suspension or
material limitation in trading in the Company's securities on NASDAQ; (iii) a
general moratorium on commercial banking activities declared by either Federal
or New York or California State authorities; or (iv) the outbreak or escalation
of hostilities involving the United States or the declaration by the United
States of a national emergency or war, if the effect of

                                       12
<PAGE>

any such event specified in this clause (iv) in the judgment of the
Representatives makes it impracticable or inadvisable to proceed with the public
offering or the delivery of the Shares being delivered at such Time of Delivery
on the terms and in the manner contemplated in the Prospectus;

  (h) The Shares to be sold at such Time of Delivery shall have been duly listed
for quotation on NASDAQ;

  (i) The Company has obtained and delivered to the Underwriters executed copies
of an agreement from each stockholder listed on Schedule II hereto,
substantially to the effect set forth in Subsection 1(p) hereof in form and
substance satisfactory to you;

  (j) The Company shall have complied with the provisions of Section 5(c) hereof
with respect to the furnishing of prospectuses on the New York Business Day next
succeeding the date of this Agreement; and

  (k) The Company shall have furnished or caused to be furnished to you at such
Time of Delivery certificates of officers of the Company satisfactory to you as
to the accuracy of the representations and warranties of the Company herein at
and as of such Time of Delivery, as to the performance by the Company of all of
its obligations hereunder to be performed at or prior to such Time of Delivery,
as to the matters set forth in subsections (a) and (e) of this Section and as to
such other matters as you may reasonably request.

  (l) Townsend and Townsend and Crew LLP (TTC), special counsel for the Company,
shall have furnished to you its written opinion dated such Time of Delivery, in
form and substance satisfactory to you, to the effect that:

    (i)     To such counsel's knowledge, except as generally described in the
Prospectus, the Company has not received any notice of infringement or of
conflict with rights or claims of others with respect to any intellectual
property, except for an advisory letter from Ixsys Corporation, which TTC
understands has been discussed with you, and with respect to which TTC has
provided opinions of invalidity of the Ixsys patents and noninfringement of the
Company's activities with respect to the Ixsys patents. Except as generally
described in the Prospectus, nothing has come to such counsel's attention that
has led them to believe that any patents of others are infringed by the
processes or practices of the Company, or by the manufacture, use or sale of the
Company's products.

    (ii)    To such counsel's knowledge, except (a) in connection with
assertions or inquiries made by Patent Office examiners in the ordinary course
of the prosecution of the Company's patent applications in the Patent Office and
an opposition in the Australian Patent Office, which TTC understands has been
discussed with you or (b) as may be generally described in the Prospectus, there
is not pending or threatened in writing any action, suit, proceeding or claim
(x) challenging the validity or scope of the patent applications held by or
licensed to the Company or (y) asserting that any patent is infringed by the
processes or practices of the Company, or by the manufacture, use or sale of the
Company's products.

    (iii)   Such counsel, as patent counsel to the Company, except as may be
generally described in the Prospectus, do not know of any pending or threatened
litigation or any governmental proceeding, statute or regulation which would
affect the Company's intellectual property rights to patents or patent
applications, or under any instrument or other document relating thereof.

    (iv)    Such counsel believes that the descriptions relating to patents and
patent applications with respect to all patent matters under "Risk Factors -
Any Inability to Adequately

                                       13
<PAGE>

Protect Our Proprietary Technologies Could Harm Our Competitive Position", "Risk
Factors - Litigation or Other Proceedings or Third Party Claims of Intellectual
Property Infringement Could Require Us to Spend Time and Money and Could Shut
Down Some of Our Operations", Business - The Maxygen Solution", "Business -
Maxygen's Molecular Breeding Technologies" and "Business - Intellectual Property
and Technology Licenses" in the Prospectus are accurate and fairly present the
information shown, and such counsel does not know of any instrument or other
document relating to patents or patent applications required to be summarized or
described therein or to be filed as an exhibit thereto which is not so
summarized, described or filed.

    (v)     Such counsel does not believe that the statements relating to
patents, patent applications and patent matters under "Risk Factors - Any
Inability to Adequately Protect Our Proprietary Technologies Could Harm Our
Competitive Position", "Risk Factors - Litigation or Other Proceedings or Third
Party Claims of Intellectual Property Infringement Could Require Us to Spend
Time and Money and Could Shut Down Some of Our Operations", Business - The
Maxygen Solution", "Business - Maxygen's Molecular Breeding Technologies" and
"Business -Intellectual Property and Technology Licenses" in the Registration
Statement such counsel reviewed, contained any untrue statement of a material
fact or omitted to state any material fact which was required to be stated
therein from a patent law perspective or necessary in order to make the
statements therein not misleading.

  8.     (a)  The Company will indemnify and hold harmless each Underwriter
against any losses, claims, damages or liabilities, joint or several, to which
such Underwriter may become subject, under the Act or otherwise, insofar as such
losses, claims, damages or liabilities (or actions in respect thereof) arise out
of or are based upon an untrue statement or alleged untrue statement of a
material fact contained in any Preliminary Prospectus, the Registration
Statement or the Prospectus, or any amendment or supplement thereto, or arise
out of or are based upon the omission or alleged omission to state therein a
material fact required to be stated therein or necessary to make the statements
therein not misleading, and will reimburse each Underwriter for any legal or
other expenses reasonably incurred by such Underwriter in connection with
investigating or defending any such action or claim as such expenses are
incurred; provided, however, that the Company shall not be liable in any such
case to the extent that any such loss, claim, damage or liability arises out of
or is based upon an untrue statement or alleged untrue statement or omission or
alleged omission made in any Preliminary Prospectus, the Registration Statement
or the Prospectus or any such amendment or supplement in reliance upon and in
conformity with written information furnished to the Company by any Underwriter
through Goldman, Sachs & Co. expressly for use therein.

  (b) Each Underwriter will indemnify and hold harmless the Company against any
losses, claims, damages or liabilities to which the Company may become subject,
under the Act or otherwise, insofar as such losses, claims, damages or
liabilities (or actions in respect thereof) arise out of or are based upon an
untrue statement or alleged untrue statement of a material fact contained in any
Preliminary Prospectus, the Registration Statement or the Prospectus, or any
amendment or supplement thereto, or arise out of or are based upon the omission
or alleged omission to state therein a material fact required to be stated
therein or necessary to make the statements therein not misleading, in each case
to the extent, but only to the extent, that such untrue statement or alleged
untrue statement or omission or alleged omission was made in any Preliminary
Prospectus, the Registration Statement or the Prospectus or any such amendment
or supplement in reliance upon and in conformity with written information
furnished to the Company by such Underwriter through Goldman, Sachs & Co.
expressly for use therein; and will reimburse the Company for any legal or

                                       14
<PAGE>

other expenses reasonably incurred by the Company in connection with
investigating or defending any such action or claim as such expenses are
incurred.

  (c) Promptly after receipt by an indemnified party under subsection (a) or (b)
above of notice of the commencement of any action, such indemnified party shall,
if a claim in respect thereof is to be made against the indemnifying party under
such subsection, notify the indemnifying party in writing of the commencement
thereof; but the omission so to notify the indemnifying party shall not relieve
it from any liability which it may have to any indemnified party otherwise than
under such subsection.  In case any such action shall be brought against any
indemnified party and it shall notify the indemnifying party of the commencement
thereof, the indemnifying party shall be entitled to participate therein and, to
the extent that it shall wish, jointly with any other indemnifying party
similarly notified, to assume the defense thereof, with counsel satisfactory to
such indemnified party (who shall not, except with the consent of the
indemnified party, be counsel to the indemnifying party), and, after notice from
the indemnifying party to such indemnified party of its election so to assume
the defense thereof, the indemnifying party shall not be liable to such
indemnified party under such subsection for any legal expenses of other counsel
or any other expenses, in each case subsequently incurred by such indemnified
party, in connection with the defense thereof other than reasonable costs of
investigation.  No indemnifying party shall, without the written consent of the
indemnified party, effect the settlement or compromise of, or consent to the
entry of any judgment with respect to, any pending or threatened action or claim
in respect of which indemnification or contribution may be sought hereunder
(whether or not the indemnified party is an actual or potential party to such
action or claim) unless such settlement, compromise or judgment (i) includes an
unconditional release of the indemnified party from all liability arising out of
such action or claim and (ii) does not include a statement as to or an admission
of fault, culpability or a failure to act, by or on behalf of any indemnified
party.

  (d) If the indemnification provided for in this Section 8 is unavailable to or
insufficient to hold harmless an indemnified party under subsection (a) or (b)
above in respect of any losses, claims, damages or liabilities (or actions in
respect thereof) referred to therein, then each indemnifying party shall
contribute to the amount paid or payable by such indemnified party as a result
of such losses, claims, damages or liabilities (or actions in respect thereof)
in such proportion as is appropriate to reflect the relative benefits received
by the Company on the one hand and the Underwriters on the other from the
offering of the Shares.  If, however, the allocation provided by the immediately
preceding sentence is not permitted by applicable law or if the indemnified
party failed to give the notice required under subsection (c) above, then each
indemnifying party shall contribute to such amount paid or payable by such
indemnified party in such proportion as is appropriate to reflect not only such
relative benefits but also the relative fault of the Company on the one hand and
the Underwriters on the other in connection with the statements or omissions
which resulted in such losses, claims, damages or liabilities (or actions in
respect thereof), as well as any other relevant equitable considerations.  The
relative benefits received by the Company on the one hand and the Underwriters
on the other shall be deemed to be in the same proportion as the total net
proceeds from the offering (before deducting expenses) received by the Company
bear to the total underwriting discounts and commissions received by the
Underwriters, in each case as set forth in the table on the cover page of the
Prospectus.  The relative fault shall be determined by reference to, among other
things, whether the untrue or alleged untrue statement of a material fact or the
omission or alleged omission to state a material fact relates to information
supplied by the Company on the one hand or the Underwriters on the other and the
parties' relative intent, knowledge, access to information and

                                       15
<PAGE>

opportunity to correct or prevent such statement or omission. The Company and
the Underwriters agree that it would not be just and equitable if contributions
pursuant to this subsection (d) were determined by pro rata allocation (even if
the Underwriters were treated as one entity for such purpose) or by any other
method of allocation which does not take account of the equitable considerations
referred to above in this subsection (d). The amount paid or payable by an
indemnified party as a result of the losses, claims, damages or liabilities (or
actions in respect thereof) referred to above in this subsection (d) shall be
deemed to include any legal or other expenses reasonably incurred by such
indemnified party in connection with investigating or defending any such action
or claim. Notwithstanding the provisions of this subsection (d), no Underwriter
shall be required to contribute any amount in excess of the amount by which the
total price at which the Shares underwritten by it and distributed to the public
were offered to the public exceeds the amount of any damages which such
Underwriter has otherwise been required to pay by reason of such untrue or
alleged untrue statement or omission or alleged omission. No person guilty of
fraudulent misrepresentation (within the meaning of Section 11(f) of the Act)
shall be entitled to contribution from any person who was not guilty of such
fraudulent misrepresentation. The Underwriters' obligations in this subsection
(d) to contribute are several in proportion to their respective underwriting
obligations and not joint.

  (e) The obligations of the Company under this Section 8 shall be in addition
to any liability which the Company may otherwise have and shall extend, upon the
same terms and conditions, to each person, if any, who controls any Underwriter
within the meaning of the Act; and the obligations of the Underwriters under
this Section 8 shall be in addition to any liability which the respective
Underwriters may otherwise have and shall extend, upon the same terms and
conditions, to each officer and director of the Company and to each person, if
any, who controls the Company within the meaning of the Act.

  9.     (a)  If any Underwriter shall default in its obligation to purchase the
Shares which it has agreed to purchase hereunder at a Time of Delivery, you may
in your discretion arrange for you or another party or other parties to purchase
such Shares on the terms contained herein.  If within thirty-six hours after
such default by any Underwriter you do not arrange for the purchase of such
Shares, then the Company shall be entitled to a further period of thirty-six
hours within which to procure another party or other parties satisfactory to you
to purchase such Shares on such terms.  In the event that, within the respective
prescribed periods, you notify the Company that you have so arranged for the
purchase of such Shares, or the Company notifies you that it has so arranged for
the purchase of such Shares, you or the Company shall have the right to postpone
such Time of Delivery for a period of not more than seven days, in order to
effect whatever changes may thereby be made necessary in the Registration
Statement or the Prospectus, or in any other documents or arrangements, and the
Company agrees to file promptly any amendments to the Registration Statement or
the Prospectus which in your opinion may thereby be made necessary. The term
"Underwriter" as used in this Agreement shall include any person substituted
under this Section with like effect as if such person had originally been a
party to this Agreement with respect to such Shares.

  (b) If, after giving effect to any arrangements for the purchase of the Shares
of a defaulting Underwriter or Underwriters by you and the Company as provided
in subsection (a) above, the aggregate number of such Shares which remains
unpurchased does not exceed one-eleventh of the aggregate number of all the
Shares to be purchased at such Time of Delivery, then the Company shall have the
right to require each non-defaulting Underwriter to purchase the number of
shares

                                       16
<PAGE>

which such Underwriter agreed to purchase hereunder at such Time of Delivery
and, in addition, to require each non-defaulting Underwriter to purchase its pro
rata share (based on the number of Shares which such Underwriter agreed to
purchase hereunder) of the Shares of such defaulting Underwriter or Underwriters
for which such arrangements have not been made; but nothing herein shall relieve
a defaulting Underwriter from liability for its default.

  (c) If, after giving effect to any arrangements for the purchase of the Shares
of a defaulting Underwriter or Underwriters by you and the Company as provided
in subsection (a) above, the aggregate number of such Shares which remains
unpurchased exceeds one-eleventh of the aggregate number of all the Shares to be
purchased at such Time of Delivery, or if the Company shall not exercise the
right described in subsection (b) above to require non-defaulting Underwriters
to purchase Shares of a defaulting Underwriter or Underwriters, then this
Agreement (or, with respect to the Second Time of Delivery, the obligations of
the Underwriters to purchase and of the Company to sell the Optional Shares)
shall thereupon terminate, without liability on the part of any non-defaulting
Underwriter or the Company, except for the expenses to be borne by the Company
and the Underwriters as provided in Section 6 hereof and the indemnity and
contribution agreements in Section 8 hereof; but nothing herein shall relieve a
defaulting Underwriter from liability for its default.

  10.    The respective indemnities, agreements, representations, warranties and
other statements of the Company and the several Underwriters, as set forth in
this Agreement or made by or on behalf of them, respectively, pursuant to this
Agreement, shall remain in full force and effect, regardless of any
investigation (or any statement as to the results thereof) made by or on behalf
of any Underwriter or any controlling person of any Underwriter, or the Company,
or any officer or director or controlling person of the Company, and shall
survive delivery of and payment for the Shares.

  11.    If this Agreement shall be terminated pursuant to Section 9 hereof, the
Company shall not then be under any liability to any Underwriter except as
provided in Sections 6 and 8 hereof; but, if for any other reason, any Shares
are not delivered by or on behalf of the Company as provided herein, the Company
will reimburse the Underwriters through you for all out-of-pocket expenses
approved in writing by you, including fees and disbursements of counsel,
reasonably incurred by the Underwriters in making preparations for the purchase,
sale and delivery of the Shares not so delivered, but the Company shall then be
under no further liability to any Underwriter except as provided in Sections 6
and 8 hereof.

  12.    In all dealings hereunder, you shall act on behalf of each of the
Underwriters, and the parties hereto shall be entitled to act and rely upon any
statement, request, notice or agreement on behalf of any Underwriter made or
given by you jointly or by Goldman, Sachs & Co. on behalf of you as the
representatives.

  All statements, requests, notices and agreements hereunder shall be in
writing, and if to the Underwriters shall be delivered or sent by mail, telex or
facsimile transmission to you as the representatives in care of Goldman, Sachs &
Co., 32 Old Slip, 21st Floor, New York, New York  10005, Attention: Registration
Department; and if to the Company shall be delivered or sent by mail to the
address of the Company set forth in the Registration Statement, Attention:
Secretary; provided, however, that any notice to an Underwriter pursuant to
Section 8(c) hereof shall be delivered or sent by mail, telex or facsimile
transmission to such Underwriter at its address set forth in its Underwriters'
Questionnaire, or telex constituting such Questionnaire, which address will be
supplied to the

                                       17
<PAGE>

Company by you upon request. Any such statements, requests, notices or
agreements shall take effect upon receipt thereof.

  13.    This Agreement shall be binding upon, and inure solely to the benefit
of, the Underwriters, the Company and, to the extent provided in Sections 8 and
10 hereof, the officers and directors of the Company and each person who
controls the Company or any Underwriter, and their respective heirs, executors,
administrators, successors and assigns, and no other person shall acquire or
have any right under or by virtue of this Agreement. No purchaser of any of the
Shares from any Underwriter shall be deemed a successor or assign by reason
merely of such purchase.

  14.    Time shall be of the essence of this Agreement.  As used herein, the
term "business day" shall mean any day when the Commission's office in
Washington, D.C. is open for business.

  15.    This Agreement shall be governed by and construed in accordance with
the laws of the State of New York.

  16.    This Agreement may be executed by any one or more of the parties hereto
in any number of counterparts, each of which shall be deemed to be an original,
but all such counterparts shall together constitute one and the same instrument.

                                       18
<PAGE>

  If the foregoing is in accordance with your understanding, please sign and
return to us seven (7) counterparts hereof, and upon the acceptance hereof by
you, on behalf of each of the Underwriters, this letter and such acceptance
hereof shall constitute a binding agreement between each of the Underwriters and
the Company.  It is understood that your acceptance of this letter on behalf of
each of the Underwriters is pursuant to the authority set forth in a form of
Agreement among Underwriters, the form of which shall be submitted to the
Company for examination upon request, but without warranty on your part as to
the authority of the signers thereof.

                                       Very truly yours,

                                       Maxygen, Inc.

                                       By: ____________________________________
                                           Name:
                                           Title:

Accepted as of the date hereof:

Goldman, Sachs & Co.
Credit Suisse First Boston Corporation
FleetBoston Robertson Stephens Inc.
Invemed Associates LLC

By: __________________________________
          Goldman, Sachs & Co.

 On behalf of each of the Underwriters

                                       19
<PAGE>

<TABLE>
<CAPTION>
- -------------------------------------------------------------------------------------------------------------------
                                                        SCHEDULE I
- -------------------------------------------------------------------------------------------------------------------
                                                                                                 Number of Optional
- -------------------------------------------------------------------------------------------------------------------
                                                                                                    Shares to be
- -------------------------------------------------------------------------------------------------------------------
                                                                     Total Number of                Purchased if
- -------------------------------------------------------------------------------------------------------------------
                                                                       Firm Shares                 Maximum Option
- -------------------------------------------------------------------------------------------------------------------
                      Underwriter                                     to be Purchased                 Exercised
                      -----------                                    ---------------               --------------
- -------------------------------------------------------------------------------------------------------------------
<S>                                                                  <C>                         <C>
Goldman, Sachs & Co...........................................
- -------------------------------------------------------------------------------------------------------------------
Credit Suisse First Boston Corporation........................
- -------------------------------------------------------------------------------------------------------------------
FleetBoston Robertson Stephens Inc............................
- -------------------------------------------------------------------------------------------------------------------
Invemed Associates LLC........................................
- -------------------------------------------------------------------------------------------------------------------
- -------------------------------------------------------------------------------------------------------------------
- -------------------------------------------------------------------------------------------------------------------
- -------------------------------------------------------------------------------------------------------------------
- -------------------------------------------------------------------------------------------------------------------
- -------------------------------------------------------------------------------------------------------------------
- -------------------------------------------------------------------------------------------------------------------
- -------------------------------------------------------------------------------------------------------------------
- -------------------------------------------------------------------------------------------------------------------
- -------------------------------------------------------------------------------------------------------------------
- -------------------------------------------------------------------------------------------------------------------
- -------------------------------------------------------------------------------------------------------------------
        Total.................................................
- -------------------------------------------------------------------------------------------------------------------
</TABLE>

                                       20
<PAGE>

                                  SCHEDULE II

Schedule IIA:
Russell J. Howard
Russell and Maureen Howard Trust
Simba Gill
Michael Rabson
Willem P.C. Stemmer
John Bedbrook
Howard A. Simon
Norman Kruse
Isaac Stein
Stein 1995 Revocable Trust
Stein Partners
Robert J. Glaser
M.R.C. Greenwood
Adrian Hennah
Gordon Ringold
Gregory Zarucki Ringold 1998 Trust
Alexander Zarucki Ringold 1998 Trust
Melanie Gault-Ringold 1998 Trust
George Poste
Julian N. Stern
Glaxo Wellcome International BV
Glaxo Wellcome plc
Technogen Associates, L.P.
Technogen Enterprises, L.L.C.
Lombard Odier & Cie

Schedule IIB:
R.A. Investment Group and Affiliates
R.A. Investment Group
Pioneer Hi-Bred International
Pioneer Overseas Corporation
Alejandro Zaffaroni
Zaffaroni Family Partnership L.P.
Zaffaroni Revocable Trust 1/24/86
Alejandro & Lida Zaffroni Revoc. Trust UTA 1-24-86
Elisa Zaffaroni Trust UTA 4-15-89
Charles Adam Zaffaroni Trust UTD 12/29/88
Alexander Peter Zaffaroni Trust UTD 12/29/88
The Zaffaroni Family Partnership L.P.
Alexander Peter Zaffaroni Trust UTD 04/15/89
Charles Adam Zaffaroni Trust UTD 04/15/89
Miller Family Investors, L.L.C.
Jerry Cohn
[Other Directed Share Purchasers Allocated Shares by Dr. Zaffaroni and R.A.
Investment Group]

                                       21

<PAGE>

                 [Heller Ehrman White & McAuliffe Letterhead]
                                                                     EXHIBIT 5.1

March 2, 2000


Maxygen, Inc.
515 Galveston Drive
Redwood City, California 94063
                                                                      22800-0001
Re:    Registration Statement on Form S-1


Dear:  Ladies and Gentlemen:

       We have acted as counsel to Maxygen, Inc., a Delaware corporation (the
"Company"), in connection with the Registration Statement on Form S-1 to be
filed with the Securities and Exchange Commission on March 3, 2000 (as may be
further amended or supplemented, the "Registration Statement") for the purpose
of registering under the Securities Act of 1933, as amended, 1,725,000 shares of
its authorized but unissued Common Stock, par value $.0001 per share (the
"Shares"). The Shares, which include up to 225,000 shares of the Company's
Common Stock issuable pursuant to an over-allotment option granted to the
underwriters, are to be sold pursuant to an Underwriting Agreement (the
"Underwriting Agreement") among the Company and Goldman, Sachs & Co., Robertson
Stephens, Invemed Associates and Credit Suisse First Boston, as representatives
of the several underwriters named in Schedule I to the Underwriting Agreement.

       We have assumed the authenticity of all records, documents and
instruments submitted to us as originals, the genuineness of all signatures, the
legal capacity of natural persons and the conformity to the originals of all
records, documents and instruments submitted to us as copies.

       In rendering our opinion, we have examined the following records,
documents and instruments:

  (a)  The Amended and Restated Certificate of Incorporation of the Company,
       certified by the Delaware Secretary of State as of March 2, 2000, and
       certified to us by an officer of the Company as being complete and in
       full force as of the date of this opinion;

  (b)  The Amended and Restated Bylaws of the Company certified to us by an
       officer of the Company as being complete and in full force and effect as
       of the date of this opinion;

  (c)  A Certificate of an officer of the Company (i) attaching records
       certified to us as constituting all records of proceedings and actions of
       the Board of Directors, including any committee
<PAGE>

                                                                   Maxygen, Inc.
                                                                   March 2, 2000
                                                                          Page 2

       thereof, and stockholders of the Company relating to the Shares, and the
       Registration Statement, and (ii) certifying as to certain factual
       matters;

  (d)  The Registration Statement; and

  (e)  A letter from ChaseMellon Shareholder Services, L.L.C., dated as of March
       2, 2000, as to the number of shares of the Company's Common Stock that
       were outstanding on March 1, 2000.

       This opinion is limited to the federal law of the United States of
America and the General Corporation Law of the State of Delaware, and we
disclaim any opinion as to the laws of any other jurisdiction. We further
disclaim any opinion as to any other statute, rule, regulation, ordinance, order
or other promulgation of any other jurisdiction or any regional or local
governmental body or as to any related judicial or administrative opinion.

       Based upon the foregoing and our examination of such questions of law as
we have deemed necessary or appropriate for the purpose of this opinion, and
assuming that (i) the Registration Statement becomes and remains effective
during the period when the Shares are offered and sold, (ii) the Underwriting
Agreement signed by the parties thereto conforms in all material respects to the
draft filed as Exhibit 1.1 to the Registration Statement, (iii) the currently
unissued Shares to be sold by the Company are issued, delivered and paid for in
accordance with the terms of the Underwriting Agreement, (iv) appropriate
certificates evidencing the Shares will be executed and delivered by the
Company, and (v) all applicable securities laws are complied with, it is our
opinion that, when issued by the Company, the currently unissued Shares covered
by the Registration Statement will be legally issued, fully paid and
nonassessable.

       This opinion is rendered to you in connection with the Registration
Statement and is solely for your benefit. This opinion may not be relied upon by
you for any other purpose, or relied upon by any other person, firm, corporation
or other entity for any purpose, without our prior written consent. We disclaim
any obligation to advise you of any change of law that occurs, or any facts of
which we may become aware, after the date of this opinion.

       We hereby consent to the filing of this opinion as an exhibit to the
Registration Statement.

                                        Very truly yours,



                                        /s/ Heller Ehrman White & McAuliffe

<PAGE>

                                                                   EXHIBIT 10.15


THIS COLLABORATIVE RESEARCH AND DEVELOPMENT AGREEMENT (the "Agreement") is made
as of the 19th day of January, 2000 (the "Effective Date")

BETWEEN

TECHNOLOGICAL RESOURCES PTY LIMITED (ACN 002 183 557) through its business unit,
Research and Technology Development, of 55 Collins Street, Melbourne, Victoria
3000, a wholly owned subsidiary of Rio Tinto Limited ("TRPL")

AND

MAXYGEN INC. of 515 Galveston Drive, Redwood City, CA 94063, United States of
America ("MAXYGEN")

PURPOSE OF AGREEMENT

      A.    TRPL wishes to develop Carbon Sequestration technologies for use in
            connection with *******, and for other purposes more generally.

      B.    MAXYGEN has expertise in developing biotechnologies, particularly
            those relating to gene shuffling, across a broad range of
            applications.

      C.    TRPL and MAXYGEN wish to collaborate through the sharing of their
            expertise to develop a particular technology for Carbon
            Sequestration.

      D.    The purpose of this Agreement is to establish the terms and
            conditions upon which the Project will be established, carried out
            and commercialized by TRPL and MAXYGEN.

IT IS AGREED

1.    DEFINITIONS AND INTERPRETATION

      For purposes of this Agreement, the following defined words shall have the
      meanings indicated:

1.1   "Affiliate" means any corporation, firm, limited liability company,
      partnership or other entity that directly or indirectly controls or is
      controlled by or is under common control with MAXYGEN. As used in this
      paragraph, control includes, without limitation, ownership, directly or
      through one or more affiliates, of fifty percent (50%) or more of the
      shares of stock entitled to vote for the election of directors, in the
      case of a corporation, or fifty percent (50%) or more of the equity
      interests in the case of any other type of legal entity, status as a
      general partner in any partnership, or any other arrangement whereby a
      party controls or has the right to control the board of directors or
      equivalent governing body of a corporation or other entity, or if such
      level of ownership or control is prohibited in any country, any entity
      owned or controlled by or owning or

THE SYMBOL "*******" IS USED TO INDICATE THAT A PORTION OF THE EXHIBIT HAS BEEN
OMITTED AND FILED SEPARATELY WITH THE COMMISSION.  CONFIDENTIAL TREATMENT HAS
BEEN REQUESTED WITH RESPECT TO THE OMITTED PORTIONS.
<PAGE>

      controlling at the maximum control or ownership right permitted in the
      country where such entity exists;

1.2   "Agreement" means this agreement, including its Schedules, and any
      amendment to it agreed to in writing by the Parties;

1.3   "Applications" means each of the TRPL Coal Applications, the Non-TRPL Coal
      Applications, the Biomass Applications, the Non-Renewable Energy
      Applications, and the Value Added Products Applications;

1.4   "Background Technology" means the MAXYGEN Background Technology and/or the
      TRPL Background Technology, as appropriate;

1.5   "Biomass" means organisms, living or dead, or the products of living
      organisms;

1.6   "Biomass Applications" means *******;

1.7   "Business Unit" means the TRPL Business unit, Research and Technology
      Development;

1.8   "Carbon Entity" means the joint venture vehicle or any other legal entity
      (if any) established by the Parties or with the authority of the Parties,
      to Exploit the Project Technology for the Applications;

1.9   "Carbon Sequestration" means *******;

1.10  "Confidential Information" means all know-how, financial information and
      other commercially valuable information in whatever form including
      unpatented inventions, trade secrets, formulae, graphs, drawings, designs,
      biological materials, samples, devices, models and other materials of
      whatever description which a Party discloses to the other Party and
      designates as Confidential Information at the time of disclosure. The
      following are exceptions to such information:

      (a)   information which is already in the public domain;

      (b)   information which hereafter becomes part of the public domain
            otherwise than as a result of an unauthorized disclosure by the
            recipient Party or its representatives;

      (c)   information which is or becomes available to the recipient Party,
            other than under an obligation of confidentiality, from a Third
            Party lawfully in possession of such information and who has the
            lawful power to disclose such information to the recipient Party;

      (d)   information which is rightfully known by the recipient Party (as
            shown by its written records) prior to the date of disclosure to it
            hereunder; or

      (e)   information which is independently developed by the recipient Party
            without any use of or reference to any Confidential Information of
            the other Party;

                                       2
<PAGE>

1.11  "Contributions" means the contributions (including funding, personnel,
      research activities and equipment, etc.) a Party will make to the Project
      as specified in the Project Plan;

1.12  "Control" or "Controlled" means possession of the ability to grant the
      licenses or sublicenses as provided for herein without violating the terms
      of any agreement or other arrangement with any Third Party;

1.13  "Exploit" and/or "Exploitation" means to use, make, have made, import,
      lease, sell, sublicense or otherwise dispose of to a Third Party, or offer
      to use, make, lease, sell, sublicense or otherwise dispose of to a Third
      Party;

1.14  "Feasibility Milestone" means Decision Milestone 2 (as defined in the
      Project Plan) for the Project established in the Project Plan;

1.15  "Gene" means any gene selected for Shuffling in the Project by the
      Management Committee pursuant to clause 3.2;

1.16  "Gene Variant" means any altered form of a Gene which meets the applicable
      criteria agreed by the Management Committee and is made in connection with
      the Project through the use of Shuffling Technology;

1.17  "Improvements" means any enhancement, modification, adaptation or
      extension to the Materials made by MAXYGEN or jointly by TRPL and MAXYGEN,
      and all Intellectual Property Rights subsisting in them;

1.18  "Intellectual Property Rights" means statutory and other proprietary
      rights in respect of trade marks, patents, circuit layouts, copyrights,
      confidential information, know-how and all other rights with respect to
      Intellectual Property as defined in Article 2 of the Convention
      Establishing the World Intellectual Property Organization of July 1967;

1.19  "Management Committee" means the management committee established pursuant
      to clause 3;

1.20  "Manufacturing Costs" means, with respect to Products sold by MAXYGEN
      (and/or its Affiliates) or TRPL (and/or RIO TINTO Group Members), as the
      case may be, (i) ******* costs related to the manufacture of Products, by
      MAXYGEN (and/or its Affiliates) or TRPL (and/or RIO TINTO Group Members),
      as the case may be, including without limitation, costs for personnel,
      materials, quality control, regulatory compliance, administrative
      expenses, subcontractors, fixed and variable manufacturing overhead costs
      and business unit or division *******, and the like, as determined and
      allocated in accordance with generally accepted accounting principles
      (GAAP), consistently applied by the applicable Party, excluding *******,
      or (ii) with respect to Products purchased by MAXYGEN (and/or its
      Affiliates) or TRPL (and/or RIO TINTO Group Members), as the case may be,
      from a Third Party manufacturer, ******* paid to the manufacturer for such
      Products;

                                       3
<PAGE>

1.21  "Materials" means any chemical or biological substances including, without
      limitation, any: (a) organic or inorganic chemical element or compound;
      (b) gene; (c) vector or construct, plasmid, phage or virus; (d) host
      organism, including bacteria and plant cells; (e) eukaryotic or
      prokaryotic cell line or expression system; (f) protein, including any
      peptide or amino acid sequence, enzyme, antibody or protein conferring
      targeting properties and any fragment of a protein or peptide or enzyme;
      (g) genetic material, including any genetic control element (e.g.,
      promoters), Gene, Gene Variant or Shuffled Gene; or (h) assay or reagent;

1.22  "MAXYGEN Background Technology" means all Materials provided by MAXYGEN
      for use in the Project and Intellectual Property Rights of MAXYGEN which
      are necessary for the conduct of the Project and made available by MAXYGEN
      for the conduct of the Project;

1.23  "MAXYGEN Field" means all uses except *******;

1.24  "Net Revenues" with respect to a particular Product means Net Sales for
      such Product, less:

      (a)   an amount for such manufacturing equal to ******* of the
            Manufacturing Costs related to such Products; and

      (b)   any expenses incurred or accrued in connection with the
            installation, packaging, labeling, marketing, sale or other
            disposition of the Products by MAXYGEN (and/or its Affiliates) or
            TRPL (and/or RIO TINTO Group Members), as the case may be, and
            general and administrative expenses relating to the preceding, as
            determined and allocated in accordance with generally accepted
            accounting principles, consistently applied by the applicable Party.

1.25  "Net Sales" means the amounts (including, without limitation, *******)
      received by MAXYGEN (and/or its Affiliates) or TRPL (and/or RIO TINTO
      Group Members), as the case may be, from Third Parties (including without
      limitation Sublicensees) with respect to the Exploitation of Products,
      less: (i) rebates, credits and cash, trade and quantity discounts,
      actually taken, (ii) excise taxes, sales, use, value added, and other
      consumption taxes and other compulsory payments to governmental
      authorities, actually paid, (iii) the cost of any shipping packages and
      packing, if billed separately, (iv) insurance costs and outbound
      transportation charges prepaid or allowed, (v) import and/or export duties
      and tariffs actually paid, and (vi) amounts allowed or credited due to
      returns or *******. All transfers of Products between MAXYGEN and/or its
      Affiliates or TRPL and/or RIO TINTO Group Members, as the case may be,
      shall be disregarded for purposes of computing Net Sales, unless the
      purchaser is the end-user of such Product;

1.26  "Non-Renewable Energy Applications" means *******;

1.27  "Non-TRPL Coal Applications" means *******;

                                       4
<PAGE>

1.28  "Objective" means the development, through the use of Shuffling
      Technology, of Shuffled Genes which have an enhanced capability in Carbon
      Sequestration with a view to Exploitation by the Parties as set forth in
      this Agreement;

1.29  "Parties" means the parties to this Agreement and their successors and
      permitted assigns and "Party" means one of them;

1.30  "Phase I" means the first phase of the Project as described in the Project
      Plan, up to achievement of the Feasibility Milestone;

1.31  "Phase II" means the second phase of the Project involving further
      research for the scale-up the development of a prototype apparatus for the
      Applications utilizing Shuffled Genes or proteins expressed therefrom;

1.32  "Phase II Milestones" means the milestones established by the Parties in
      writing at the commencement of Phase II which milestones are directed at
      achieving the Objective;

1.33  "Product" means any product that is, or incorporates or is made through
      the use of one or more Shuffled Genes or proteins expressed therefrom. Any
      process utilizing one or more Shuffled Genes or proteins expressed
      therefrom shall also be considered a Product;

1.34  "Project" means the research activities comprised in Phase I and Phase II
      which are to be undertaken by the Parties pursuant to this Agreement as
      described more particularly in the Project Plan;

1.35  "Project Commencement Date" means the date thirty (30) days after the
      Effective Date or such earlier date as the Parties may agree in writing to
      commence Phase I of the Project;

1.36  "Project Plan" means the initial plan referred to in clause 2.1 which has
      been agreed by the parties as of the Effective Date for the conduct of the
      Project, which plan may be amended from time to time by the Management
      Committee;

1.37  "Project Technology" means all ideas, inventions, discoveries,
      innovations, data, software, databases, results, information, reports,
      samples, Materials, Improvements, Shuffled Genes, prototypes and
      artifacts, whether or not patentable, instructions, processes and
      formulae, including, without limitation, biological, chemical, physical
      and analytical, safety, manufacturing and quality control data and
      information, in each case, which is/are conceived or reduced to practice
      or otherwise developed or made or the utility of which for the Objective
      is determined or discovered by either Party, or a Third Party on behalf of
      a Party, as part of the conduct of the Project during the Project Term,
      and all Intellectual Property Rights subsisting in the foregoing;

1.38  "Project Term" means the period beginning on the Project Commencement Date
      and ending on the third anniversary of the Project Commencement Date or as
      extended or subject to earlier termination in accordance with clause 2.2;

                                       5
<PAGE>

1.39  "Revenues" shall mean:

      (a)   the ******* by MAXYGEN (and/or its Affiliates) or TRPL (and/or RIO
            TINTO Group Members), as the case may be, for:

                  (1)   ******* from Sublicensees with respect to *******;

                  (2)   ******* from Sublicensees with respect to *******;

                  (3)   ******* of Products by Sublicensees;

                  (4)   ******* for Products; and

                  (5)   all other consideration (including, without limitation,
            ******* received by MAXYGEN (and/or its Affiliates) or TRPL (and/or
            RIO TINTO Group Members), as the case may be, attributable to the
            use of one or more Products;

            LESS, in the case of (3), (4) and/or (5) above, on a Product-by-
            Product basis, amounts paid by MAXYGEN (and/or its Affiliates) or
            TRPL (and/or RIO TINTO Group Members), as the case may be, to Third
            Parties for Intellectual Property Rights to manufacture, use, import
            or sell such Product.

      (b)   In the event that a Product is sold in combination with one or more
            other product(s), components, ingredients or active agent(s) which
            are not Products, Revenues from such sales of such Product shall be
            calculated by multiplying the Revenues of that combination by the
            fraction A/(A + B), where A is the gross selling price of the
            Product sold separately and B is the gross selling price of the
            other product, components, ingredient or active agent(s) sold
            separately. In the event that no such separate sales are made by the
            Party, Net Sales for revenue sharing determination shall be as
            reasonably allocated by the Party between such Product and such
            other product, components, ingredient or agent, based upon their
            relative importance and proprietary protection. In the event that
            the other Party believes such allocation is inequitable and the
            Parties are unable to resolve such dispute after bona fide
            negotiations in good faith, the matter may be submitted to
            arbitration pursuant to clause 23 below.

1.40  "RIO TINTO Associate" means a corporation or unincorporated joint venture
      or other business association regulated by contractual arrangement in
      which, as of December 31, 1999, a RIO TINTO Group Member has:

      (a)   not less than a 40% shareholding or participating interest; or

      (b)   if less than a 40% shareholding or participating interest, a
            shareholding or participating interest of at least 25%, provided
            that such shareholding or participating interest is equal to or
            greater than any other shareholding or participating interest;

                                       6
<PAGE>

1.41  "RIO TINTO Group Member" means Technological Resources Pty Limited, Rio
      Tinto Corporation plc (of 6 St James's Square, London, England), Rio Tinto
      Limited, and all RIO TINTO Associates having such status as of 31 December
      1999;

1.42  "Schedule" means any schedule to this Agreement;

1.43  "Shuffled Gene" means (i) any Gene Variant that the Management Committee
      designates as meeting applicable criteria established by the Management
      Committee, and (ii) any Shuffled Gene Derivative;

1.44  "Shuffled Gene Derivative" means any modified form of a Shuffled Gene
      designated by the Management Committee, which modification is developed
      from or made to the Shuffled Gene by any means, including without
      limitation, any codon modified variant, splice variant, mutation,
      derivative or variant of a Shuffled Gene, and any fragment(s) of the
      preceding;

1.45  "Shuffle", "Shuffled" and "Shuffling" means the recombination and/or
      rearrangement and/or mutation of genetic material for the creation of
      genetic diversity using intellectual property and/or tangible property
      owned or Controlled by MAXYGEN;

1.46  "Shuffling Technology" means techniques, methodologies, processes,
      materials and/or instrumentation useful for Shuffling, and generally
      applicable screening techniques, methodologies, or processes of using the
      resulting genetic material to identify potential usefulness;

1.47  "Sublicensee" means an entity (other than Affiliates in the case of
      MAXYGEN and RIO TINTO Group Members in the case of TRPL) to whom TRPL or
      MAXYGEN, as the case may be, has granted a license or sublicense to
      Exploit Products;

1.48  "Third Party" means any person other than TRPL, a RIO TINTO Group Member,
      MAXYGEN, or an Affiliate of MAXYGEN;

1.49  TRPL Background Technology" means all Materials provided by TRPL for use
      in the Project and Intellectual Property Rights of TRPL which are
      necessary for the conduct of the Project and made available by TRPL for
      the conduct of the Project;

1.50  "TRPL Coal Applications" means *******;

1.51  "TRPL Field" means *******.

1.52  "Value Added Products Applications" means *******.

1.53  Interpretation.  In this Agreement, except where the context indicates to
      the contrary:

      (a)   the expression "person" includes an individual, a body corporate, a
            joint venture, a trust, an agency or other body;

                                       7
<PAGE>

      (b)   words importing the singular will include the plural (and vice
            versa) and words denoting a given gender will include all other
            genders;

      (c)   headings are for convenience only and will not affect interpretation
            of this Agreement;

      (d)   all monetary amounts are expressed in United States currency;

      (e)   the Schedule forms part of this Agreement.

2.    PROJECT AND REPORTING

2.1   Project Plan.  The Parties will conduct the Project with the goal of
      achieving the Objective in accordance with the Project Plan. The Project
      Plan will establish: (i) the scope of the development activities which
      will be performed during each of Phase I and, if applicable, Phase II;
      (ii) objectives, work plan activities and time schedules with respect to
      the Project; and (iii) the Feasibility Milestone for Phase I and, if
      applicable, Phase II Milestone(s). The initial Project Plan has been
      agreed by the Parties in writing as of the Effective Date. The Management
      Committee will review the Project Plan on an ongoing basis and may make
      changes to it.

2.2   Term.  The term of Phase I of the Project will commence on the Project
      Commencement Date and, unless terminated earlier due to the termination of
      the Agreement pursuant to clause 2.11 or clause 14, or extended by mutual
      agreement of the Parties, will terminate upon completion of the Project
      Term. The term of Phase II of the Project, if any, shall be as agreed by
      the Parties.

2.3   Phase I and Phase II.

      (a)   Completion of Phase I.  Phase I will be completed upon achievement
            of the Feasibility Milestone or, if earlier, expiration of the
            Project Term.

      (b)   Negotiation of Phase II.  Upon achievement of the Feasibility
            Milestone, the Parties will promptly negotiate bona fide in good
            faith (i) whether to conduct Phase II, (ii) the duration of Phase
            II, (iii) the research funding to be provided in connection with
            Phase II, and (iv) appropriate modifications to the Project Plan to
            establish the Phase II Milestone(s) and the activities to be
            undertaken by the Parties in Phase II. MAXYGEN agrees for a period
            of six (6) months following the earlier of (a) achievement of
            *******, or (b) the expiration of the Project Term (such six month
            period the "Phase II Negotiation Period"), that TRPL shall be
            MAXYGEN's preferred partner for the conduct of Phase II or, subject
            to clauses 2.12 and 12.4, *******, and that during the Phase II
            Negotiation Period MAXYGEN will not, without TRPL's consent,
            negotiate with any Third Party to enter into a collaboration to
            conduct Phase II research or, subject to clauses 2.12 and 12.4,
            *******. TRPL agrees that if it is not interested in pursuing Phase
            II or other *******, it will promptly notify MAXYGEN in writing. If
            TRPL notifies MAXYGEN that it is not interested in pursuing Phase II
            research prior to expiration of the Phase II Negotiation Period, or
            if the Parties do not agree in

                                       8
<PAGE>

            writing upon the items referred to in (i) through (iv) above during
            the Phase II Negotiation Period, then (a) the Project shall
            terminate, (b) neither Party shall have any obligation to conduct
            research in Phase II, (c) TRPL shall have no obligations to provide
            research funding for Phase II, (d) MAXYGEN shall be free to pursue
            such research on its own or with any Third Party, and (e) TRPL shall
            have no rights to use any Project Technology for any purpose.

      (c)   Phase II.  If the Parties agree in writing (i) to conduct Phase II,
            (ii) the duration of Phase II, (iii) the research funding to be
            provided in connection with Phase II, and (iv) appropriate
            modifications to the Project Plan to establish the Phase II
            Milestone(s) and the activities to be undertaken by the Parties in
            Phase II, then the Parties shall devote the agreed-upon resources to
            undertake the Phase II research activities, and TRPL shall provide
            further development funding at the agreed level for the conduct of
            Phase II. Phase II will be completed upon completion of the Phase II
            Milestones or, if earlier, expiration of the time period agreed by
            the Parties for the conduct of Phase II, unless terminated earlier
            in accordance with clause 14.

2.4   Efforts.  Each of MAXYGEN and TRPL will conduct activities in connection
      with the Project as described in the Project Plan. The Parties agree to
      use reasonable efforts to carry out the Project and make their
      Contributions in the manner and at the times specified in the Project
      Plan.

2.5   Project Funding.

      (a)   TRPL Expenses.  TRPL shall be responsible for the expense of its own
            participation in the Project.

      (b)   TRPL Funding.  TRPL shall pay to MAXYGEN funding for Phase I of the
            Project of U.S. ******* each year of Phase I of the Project for
            total amount of U.S. *******. The amount of funding TRPL will pay to
            MAXYGEN for Phase II of the Project, if any, shall be agreed by the
            parties pursuant to clause 2.3(c). MAXYGEN shall have no obligation
            to expend any amount or incur any expense in connection with the
            Project except the amounts paid by TRPL to MAXYGEN pursuant to this
            clause 2.5(b). All payments pursuant to this clause 2.5(b) will be
            made inclusive of any taxes or any other charge payable in respect
            of such payment or the satisfaction by a Party of its obligations
            under this Agreement or any other matter arising out of, connected
            with or related to, this Agreement (including, without limitation,
            any applicable goods and services taxes or value added taxes, sales
            taxes or withholding taxes).

      (c)   Timing of Payments.  The amounts to be paid to MAXYGEN in connection
            with the Project will be paid quarterly, in advance. The initial
            payment for the first quarter of the first year of the Project will
            be made within fourteen (14) days after the Project Commencement
            Date, and subsequent payments will be made on or before the
            applicable quarterly anniversaries of the Project Commencement Date.

                                       9
<PAGE>

      (d)   Third Party Technology. MAXYGEN will be responsible for all payments
            due to Third Parties for the acquisition of licenses to intellectual
            property necessary for the practice of Shuffling Technology per se
            in the Project, and the costs of negotiating and preparing such
            licenses. If the Management Committee agrees that it is necessary
            for MAXYGEN to acquire any license to any other intellectual
            property or technology (e.g., a gene or Gene) from a Third Party for
            the conduct of MAXYGEN's activities in connection with the Project,
            the Management Committee will determine how such arrangements might
            proceed and what costs TRPL and/or MAXYGEN should contribute (if
            any) to the cost of acquiring the necessary license; provided, if
            the Management Committee does not agree upon allocation of costs
            between the Parties, then MAXYGEN shall have no liability hereunder
            for not acquiring or maintaining such licenses, or for failing to
            undertake or perform any research activities set forth in the
            Project Plan for which such license is necessary.

      (e)   Subcontracts.  With the prior written approval of the Management
            Committee, MAXYGEN may enter into agreements with Third Parties for
            the performance of activities in furtherance of the Project. If any
            such agreement is for the performance of activities in furtherance
            of the Project for which TRPL will be responsible for paying, TRPL
            shall be responsible for directly paying to the third party all
            compensation required to be paid pursuant to such Agreement and/or
            for reimbursing MAXYGEN for all expenses incurred by MAXYGEN in
            connection with such agreements, including, without limitation, the
            out-of-pocket costs of negotiating and preparing such agreements.

      (f)   Capital Expenditures.  If the conduct of the Project necessitates
            the purchase of specialized capital equipment, the Management
            Committee will determine whether such equipment will be purchased;
            provided, it is understood that TRPL shall not be obligated without
            its consent to provide funding in excess of the amounts set forth in
            clause 2.5(b) for Phase I or such funding as the Parties may agree
            for Phase II pursuant to clause 2.3. If the Management Committee
            approves any such purchase, TRPL and MAXYGEN in proportions to be
            agreed by them, will pay the full cost (including costs for taxes,
            shipping, etc.) for such purchases. Neither Party will have any
            obligation to purchase or to contribute to the purchase of any such
            equipment unless both Parties agree pursuant to this clause and
            provide reimbursement as agreed, and neither Party will have any
            liability hereunder for not purchasing or otherwise obtaining access
            to such equipment.

2.6   Technology Advancement Fees.  TRPL will pay to MAXYGEN an annual
      technology advancement fee of ******* each year during Phase I of the
      Project. Such funds shall be used by MAXYGEN for the development of
      Materials or Intellectual Property Rights which may be useful for the
      conduct of the Project. The first such fee will be paid to MAXYGEN on or
      before the Project Commencement Date and each subsequent fee will be paid
      to MAXYGEN on or before each anniversary of the Project Commencement Date.
      Such amounts will not be refundable nor creditable against other amounts
      due to MAXYGEN under this Agreement, and will be paid in addition to any
      amounts due from TRPL pursuant to Section 2.5(b).

                                      10
<PAGE>

2.7   Contributions to Project.

      (a)   Phase I.  During Phase I of the Project, (i) TRPL will provide
            funding for the Project as set forth in clause 2.5 and will provide
            representatives on the Management Committee appropriately qualified
            to perform their supervisory and management functions on the
            Management Committee, and (ii) MAXYGEN will:

            (i)   Use reasonable endeavors to ensure the success of the Project,
                  including without limiting the foregoing, (where required by
                  the Project Plan) devoting sufficient research personnel, and
                  laboratory facilities;

            (ii)  Engage personnel appropriately qualified to perform (where
                  required by the Project Plan), supervise, analyze and report
                  on all the results conducted pursuant to the Project; and

            (iii) Deploy such scientific, technical, financial and other
                  resources to accord the Project such priority as is necessary
                  to conduct the Project as specified in the Project Plan.

      (b)   Phase II.  During Phase II of the Project, each Party will:

            (i)   Use reasonable endeavors to ensure the success of the Project,
                  including without limiting the foregoing, (where required by
                  the Project Plan) devoting sufficient research personnel, and
                  laboratory facilities;

            (ii)  Engage personnel appropriately qualified to perform (where
                  required by the Project Plan), supervise, analyze and report
                  on all the results conducted pursuant to the Project; and

            (iii) Deploy such scientific, technical, financial and other
                  resources to accord the Project such priority as is necessary
                  to conduct the Project as specified in the Project Plan.

2.8   Selection of Genes for Shuffling.  With respect to any gene that the
      Management Committee considers for Shuffling in the Project, both Parties
      shall inform the Management Committee of any information of which it is
      aware with respect to Third Party patent applications or patents which may
      relate to the use of the gene in the Project and/or the development or
      commercialization of Products based on Shuffled Genes resulting from the
      Shuffling of such gene in the Project; provided, neither Party shall have
      any obligation to provide the Management Committee with any document which
      would result in (i) a breach of the attorney/client privilege with respect
      thereto or (ii) a breach of an obligation of confidentiality owed to a
      Third Party. It is understood that the Parties anticipate that MAXYGEN
      will propose genes for Shuffling in the Project. The Management Committee
      shall have the sole authority to select the Genes for use in the Project.
      The Management Committee shall consider technical feasibility and freedom
      to operate risks for the commercialization of Products in the selection of
      Genes.

                                      11
<PAGE>

2.9   Materials; Limited Use.  MAXYGEN shall provide reasonable quantities of
      Materials (which may include, without limitation, Shuffled Genes and/or
      Gene Variants which are potential Shuffled Genes) to TRPL as set forth in
      the Project Plan, which TRPL shall use solely for research activities in
      the conduct of the Project approved in advance by the Management
      Committee. TRPL shall provide a written summary of the results of all such
      research activity to the Management Committee. In the event that TRPL
      obtains rights to Exploit one or more Shuffled Genes as set forth in
      clause 5.2 or 5.3, TRPL shall also have the right to use Shuffled Genes
      provided hereunder for such purpose. Except in connection with the
      practice of the rights granted to TRPL in clause 5.2 and/or 5.3 hereof,
      TRPL shall not without the express prior written consent of MAXYGEN, (i)
      transfer any of the Shuffled Genes, Gene Variants or other Materials
      provided by MAXYGEN to any Third Party, (ii) use the data and information
      obtained from the research activities conducted using such Shuffled Genes,
      Gene Variants or other Materials provided by MAXYGEN (including without
      limitation any sequence information regarding the Shuffled Genes or Gene
      Variants or the proteins expressed therefrom) for any purpose other than
      the purpose of conducting research activities in the Project approved in
      advance by the Management Committee, (iii) authorize any Third Party to
      obtain or use any of the Shuffled Genes, Gene Variants or other Materials
      provided by MAXYGEN for any purpose, or (iv) use any data relating to any
      Shuffled Genes, Gene Variants or other Materials provided by MAXYGEN,
      including without limitation consensus sequences or structural motifs, to
      reverse engineer, reconstruct, synthesize or otherwise modify or copy any
      Shuffled Gene or Gene Variant or any other gene or product with similar
      biological activities, or to attempt the same.

2.10  Reporting. MAXYGEN will provide quarterly written reports (the "Report")
      to the Management Committee no less than fourteen (14) days prior to any
      scheduled meeting. Each Report will document the conduct of the Project,
      the results of the Project, expenditures incurred and milestones achieved
      for the previous quarter.

2.11  Termination.

      (a)   In the event that either Party materially breaches its obligations
            with respect to the conduct of the Project, the other Party shall
            have the right to terminate the Project and this Agreement as set
            forth in clause 14.2 below.

      (b)   In the event that Decision Milestone 1 (as set forth in the Project
            Plan) has not been met on or before the date ******* months
            following the Project Commencement Date, with three (3) months
            written notice, TRPL shall have the right to terminate the Project
            and the Agreement. In the event of such termination, (i) TRPL shall
            have no further obligation to provide Contributions following the
            effective date of such termination, and (ii) MAXYGEN shall retain
            all rights to the Project Technology as set forth in clause 5.1.

      (c)   The Parties may mutually agree to terminate the Project and the
            Agreement as provided in clause 14.3, below.

                                      12
<PAGE>

2.12  Further Agreements Relating to *******.  If Maxygen wishes to enter an
      agreement with a Third Party during the Project with respect to research
      relating to *******, Maxygen shall have the right to do so provided that
      (i) such agreement would not diminish MAXYGEN's obligations to the Project
      nor affect the rights and licenses granted to TRPL in clause 5.2(a) below,
      and (ii) MAXYGEN provides TRPL notice of the agreement prior to its
      execution. MAXYGEN agrees to discuss with TRPL in bona fide good faith the
      impact of any such an agreement on the Project, and subject to its
      confidentiality obligations, to identify to TRPL the other party to such
      agreement, the nature of the arrangement and the activities to be
      performed under such an agreement.

3.    PROJECT MANAGEMENT

3.1   Membership.  The management of the Projects will be carried out by the
      Management Committee consisting of two (2) representatives of each of TRPL
      and MAXYGEN. One representative from each of TRPL and MAXYGEN will have
      technical expertise and one representative from each of TRPL and MAXYGEN
      will have management/commercial expertise. A MAXYGEN representative will
      serve as chairperson of the Management Committee. A Party may change any
      of its appointments to the Management Committee at any time by written
      notice to the other Party. From time to time, the Management Committee may
      establish subcommittees to oversee particular activities.

3.2   Authority.  The Management Committee will be responsible for the
      oversight, direction and management of the Project. The responsibilities
      of the Management Committee will include: (i) selection of the Genes which
      will be Shuffled in the Project as set forth in clause 2.8, (ii)
      establishment of the criteria for identification of Shuffled Genes, (iii)
      designation of Gene Variants as Shuffled Genes (iv) review and
      modification of the Project Plan, (v) ensuring satisfactory flow of
      information by the review of quarterly reports and (vi) approving the
      acquisition of capital equipment and Third Party licenses. Quarterly
      reports will be available to all members of the Management Committee at
      least fourteen (14) days prior to the meeting.

3.3   Decisions.  A quorum for the Management Committee will be the full
      membership of the Management Committee as defined in clause 3.1. All
      decisions of the Management Committee must be unanimous and recorded in
      writing. If the Management Committee is unable to make a unanimous
      decision, the terms of the then-current Project Plan shall remain in
      effect. In the event that a member of the Management Committee believes
      that the then-current Project Plan should be changed and the Management
      Committee cannot agree, then the chairperson of the Management Committee
      will seek to resolve the matter pursuant to clause 23.1, but clauses 23.2,
      23.3 and 23.4 shall not apply to the resolution of such matters.

3.4   Meetings.  The Management Committee will meet on a quarterly basis in
      person or as otherwise agreed and will, additionally, communicate
      regularly by telephone, facsimile and/or video conference. Attendance at
      meetings may be in person, by telephone or by televideo conference, and
      will be at the respective expense of the participating Parties. Each Party
      recognizes the importance of the Management Committee to the success of
      the Project and will use diligent efforts to cause all of its
      representatives to attend all

                                      13
<PAGE>

      meetings of the Management Committee. With the prior approval of the
      Management Committee, other personnel of the Parties may attend Management
      Committee meetings.

3.5   Minutes.  The chairperson of the Management Committee will appoint a
      person to keep accurate minutes of its meetings. Draft minutes will be
      prepared and delivered to each Party within twenty (20) days after each
      meeting. Draft minutes will be edited by each Party's Management Committee
      representatives and will be adopted in final form with their approval and
      agreement and will record the final decisions made by the Management
      Committee. Minutes of the Management Committee meetings will be treated as
      Confidential Information of each Party.

4.    INTELLECTUAL PROPERTY RIGHTS

4.1   Ownership.

      (a)   Background Technology.  All rights to a Party's Background
            Technology remain vested solely in that Party.

      (b)   Project Technology.  MAXYGEN will own all Project Technology
            regardless of which Party conceives, reduces to practice or
            otherwise develops such Project Technology. Subject to clause 4.1(a)
            and the license rights granted pursuant to this Agreement to TRPL,
            TRPL agrees to assign and hereby irrevocably assigns to MAXYGEN its
            entire right, title and interest in the Project Technology and
            Improvements. TRPL agrees to execute in a timely manner such
            documents as MAXYGEN may request to document and perfect MAXYGEN's
            sole ownership of the Project Technology, including all Intellectual
            Property Rights subsisting in it.

      (c)   Governing Law.  It is understood and agreed that inventorship of
            Project Technology (whether or not patentable) will be determined in
            accordance with United States patent laws or the law of California,
            as applicable.

4.2   Research Licenses.  Each Party grants to the other Party a royalty-free,
      non-exclusive, non-transferable right to use its Background Technology to
      the extent necessary for the carrying out of the Project during the
      Project Term, and solely to carry out the Project; provided, (i) nothing
      hereunder grants TRPL any right or license under the MAXYGEN Background
      Technology to practice any Shuffling Technology, and (ii) nothing
      hereunder grants MAXYGEN any right or license under the TRPL Background
      Technology for any use other than performance of the Project.

4.3   Cooperation.  Each Party will do all things reasonably necessary to give
      effect to the ownership and licensing arrangements referred to in this
      clause 4.

4.4   Third Party Rights.  TRPL agrees that MAXYGEN is in the business of
      Shuffling genes on behalf of Third Parties, and that, subject to the
      limitations expressed in clause 12.4 of this Agreement, MAXYGEN has
      granted and will grant to Third Parties rights to acquire licenses for
      genes derived from Shuffling, provided always that MAXYGEN will not,

                                      14
<PAGE>

      during the Project, grant any licenses that are inconsistent with, or
      would prevent the granting of, the licenses to TRPL described in clause
      5.2(a).

      It is understood and agreed by TRPL that, even if MAXYGEN complies with
      its obligations under this Agreement, genes derived through Shuffling
      activities that MAXYGEN conducted with Third Parties in the course of
      MAXYGEN's other business activities may result in Third Party patent
      applications and patents, including patent applications and patents owned
      by such Third Parties, or owned jointly by MAXYGEN and such Third Parties,
      which could conflict with patent applications and patents owned by TRPL.
      MAXYGEN will use its reasonable efforts to avoid such conflict and, unless
      TRPL is damaged as a proximate result of such a material breach by MAXYGEN
      of this clause 4.4, then MAXYGEN will have no liability under this
      Agreement with respect to any such conflict.

4.5   No Implied Licenses.  No rights or licenses with respect to any
      intellectual property owned by MAXYGEN or TRPL are granted or will be
      deemed granted under this Agreement or in connection with it, other than
      those rights expressly granted in this Agreement.

5.    COMMERCIALIZATION OF PROJECT TECHNOLOGY

5.1   Phase I.  Except as provided in clause 5.2 or 12.4 below, or as the
      Parties may agree in writing as set forth in clause 5.3 below, MAXYGEN
      shall have the right to use, sublicense and otherwise Exploit the Project
      Technology without obligation to obtain consent of, pay royalties to, or
      otherwise account to, TRPL, and TRPL will have no rights to use MAXYGEN
      Background Technology or Project Technology for any purpose.

5.2   Phase II.  If the Parties commence the conduct of Phase II as described in
      clause 2.3 above, then each Party will have the right to Exploit the
      Project Technology and the Intellectual Property Rights subsisting in that
      technology for the Applications as set out in this clause 5.2, unless the
      Parties agree otherwise in writing as set forth in clause 5.3, below.

      (a)   To TRPL.

            (i)   Commercial License. Subject to sharing of Revenues as set
                  forth in clause 5.2(c) below, TRPL will be granted an
                  exclusive, irrevocable, worldwide, royalty-bearing license,
                  including the right to sub-license, to Exploit the Project
                  Technology in the TRPL FIELD.

            (ii)  Background Technology.  In furtherance of the license granted
                  in (i), above, and solely to the extent it is necessary to
                  exercise the foregoing license, MAXYGEN will also grant TRPL a
                  non-exclusive, irrevocable, worldwide license under the
                  MAXYGEN Background Technology to Exploit the Project
                  Technology in the TRPL Field in accordance with the foregoing
                  license, provided, in no event shall TRPL have any right or
                  license under the MAXYGEN Background Technology to practice
                  any Shuffling Technology. TRPL will not be obligated, as a
                  result of this

                                      15
<PAGE>

                  license, to pay any additional royalties to MAXYGEN beyond
                  those specified in clause 5.2(c).

      (b)   To MAXYGEN.  Subject to sharing of Revenues as set forth in clause
            5.2(c) below, and solely to the extent it is necessary for MAXYGEN
            to Exploit the Project Technology in the MAXYGEN Field, MAXYGEN will
            be granted a non-exclusive, irrevocable, royalty-bearing license to
            Exploit the TRPL Background Technology for the MAXYGEN Field.

      (c)   Revenue Sharing.  MAXYGEN and TRPL shall share in all Revenues on
            the following basis:

            Exploitation by TRPL (and/or
             RIO TINTO Group Members):                       Share of Revenues-
            ----------------------------

                                                               TRPL     MAXYGEN
                                                             --------   -------
            (i)   TRPL Coal Applications                      *******   *******

            (ii)  Non-TRPL Coal Applications                  *******   *******


            Exploitation by MAXYGEN (and/or
                   its Affiliates):                          Share of Revenues-
            -------------------------------

                                                               TRPL     MAXYGEN
                                                             --------   -------

            (iii) Biomass Applications                        *******   *******

            (iv)  Non-Renewable Energy Applications           *******   *******

            (iv)  Value Added Products Applications           *******   *******


            It is understood and agreed that the revenue sharing set forth in
            this clause 5.2(c) applies with respect to Revenues received by
            MAXYGEN (and/or its Affiliates) or TRPL (and/or RIO TINTO Group
            Members), as the case may be, attributable to the Exploitation of
            Products.

      (d)   Payment Term.  The Revenue sharing payments due from each Party
            under clause 5.2(c) shall be payable on a country-by-country and
            Product-by-Product basis, until the earlier of (i) ******* years
            following the first commercial sale or other Exploitation of such
            Product in such country or (ii) ******* years following the first
            commercial sale or other Exploitation of any Product by such Party.

      (e)   Convenience.  The Parties acknowledge that the other Party may not
            own or control patent applications or patents covering the
            manufacture, sale or use of a particular Product. However, the
            Parties agree that substantial value is contributed by the Parties'
            conduct and support of the Project in accelerated time to market,
            enhanced probability of success and the potential for multiple
            Products and, for the convenience of the Parties, the Parties (for
            their convenience) agree to

                                      16
<PAGE>

            make Revenue sharing payments set forth in clause 5.2(c) during the
            applicable period set forth in clause 5.2(d), regardless of whether
            any particular Product is covered by a patent application or patent.

      (f)   Non-Cash Consideration.  MAXYGEN (and/or its Affiliates) and TRPL
            (and/or RIO TINTO Group Members) shall not transfer Products for
            consideration other than cash or cash equivalents without providing
            the other Party fair compensation therefore consistent with this
            Agreement. If MAXYGEN (and/or its Affiliates) or TRPL (and/or RIO
            TINTO Group Members) receives any consideration in a form other than
            cash or a cash equivalent (e.g., a license under other intellectual
            property owned or Controlled by a Third Party) as part or all of the
            consideration included in the definition of Net Sales and/or
            Revenue, then MAXYGEN or TRPL, as the case may be, shall notify the
            other Party, and the fair market value of the non-cash consideration
            received by MAXYGEN (and/or its Affiliates) or TRPL (and/or RIO
            TINTO Group Members), as the case may be, for such Product shall be
            agreed by MAXYGEN and TRPL, or if the Parties are unable to agree on
            such fair market value, either Party may submit such matter to
            arbitration pursuant to clause 23 below, in order to determine the
            fair market value of such consideration.

5.3   Negotiation of Carbon Entity.  Upon completion of Phase II, the Parties
      will negotiate bona fide in good faith, for a period of three (3) months
      or, if the Phase II Milestones have been achieved in the Project, for a
      period of six (6) months (the applicable period referred to as the
      "Negotiation Period"), whether and on what terms the Parties may be
      willing to (i) establish a joint venture vehicle (the "Carbon Entity") for
      Exploitation of Project Technology for some or all Applications or (ii)
      provide for another arrangement for Exploiting the Project Technology
      (whether by grant to both Parties of non-exclusive rights, with right to
      sublicense, for Exploitation of the Project Technology for the
      Applications, or otherwise). It is understood that such negotiations will
      need to address, among other things, corporate structure of any such
      Carbon Entity, appropriate licenses to be granted to the Carbon Entity
      with respect to the Project Technology and Background Technology of the
      Parties, respective rights of the Parties in connection with the Carbon
      Entity or other agreed means of Exploitation, and appropriate revenue
      sharing terms. The Parties shall have no obligation to continue such
      negotiations after expiration of the Negotiation Period. It is understood
      and agreed that, except to the extent the Parties may otherwise expressly
      agree in writing, the exploitation rights and corresponding revenue
      sharing obligations set forth in clause 5.2 shall remain in effect.

6.    PAYMENTS; BOOKS AND RECORDS

6.1   Reports and Payments.  After the first commercial sale of a Product by a
      Party or its Sublicensees, or RIO TINTO Group Members in the case of TRPL,
      or Affiliates in the case of MAXYGEN, such Party shall make quarterly
      written reports to the other Party within ninety (90) days after the end
      of each calendar quarter, stating in each such report the Revenues
      received by such Party, by country, with respect to each applicable
      Product during the calendar quarter upon which payments are due under
      clause 5.2 and/or 5.3

                                      17
<PAGE>

      above. Concurrently with making such reports, the Party making the report
      shall pay the other Party all amounts due under clause 5.2 and/or 5.3 for
      such calendar quarter.

6.2   Payment Method.  All payments due under this Agreement shall be made by
      bank wire transfer in immediately available funds to a bank account
      designated by the receiving Party. All payments hereunder shall be made in
      U.S. dollars. In the event that the due date of any payment subject to
      clause 5 hereof is a Saturday, Sunday or national holiday, such payment
      may be paid on the following business day. Any payments that are not paid
      on the date such payments are due under this Agreement shall bear interest
      at the prime rate as reported by the Chase Manhattan Bank, New York, New
      York, on the date such payment is due, plus an additional two percent
      (2%), or, if less, at the maximum rate permitted by law, in each case
      calculated on the number of days such payment is delinquent. If any
      currency conversion shall be required in connection with the calculation
      of royalties hereunder, such conversion shall be made using the selling
      exchange rate for conversion of the foreign currency into U.S. Dollars,
      quoted for current transactions reported in The Wall Street Journal for
      the last business day of the calendar quarter to which such payment
      pertains.

6.3   Withholding Taxes.  Except as otherwise provided in clause 2.5(b), all
      amounts required to be paid pursuant to this Agreement may be paid with
      deduction for withholding for or on account of any taxes (other than taxes
      imposed on or measured by the paying Party's net income) or similar
      governmental charge imposed by an applicable jurisdiction ("Withholding
      Taxes"). Upon request, the Party making payment with such deduction shall
      provide to the other Party a certificate evidencing the payment of any
      Withholding Taxes hereunder.

6.4   Other Factors Affecting Payment.  As to countries covered by this
      Agreement which require governmental approval for remitting payments out
      of the country or which limit the amount of payments payable within the
      country, if the payments made hereunder by a Party in respect of Net
      Revenues from sales of Products exceed the rate approved or permitted by
      such country, then the rate of payment payable in respect of sales of
      Products sold in such country shall be the maximum rate approved or
      permitted by that country.

6.5   Local Payment.  If any portion of the payments due hereunder cannot be
      remitted from a country because of government control, and it is legally
      permissible to remit such payments within the country, then the Party
      obligated to make such payment shall have the obligation and the right to
      deposit in a bank of the other Party's election in such country, and in
      trust for the other Party, that portion of payments that could not be
      remitted from the country.

6.6   Inspection of Books and Records.  Each Party shall maintain accurate books
      and records which enable the calculation of the portions of Net Proceeds
      payable hereunder to be verified. The Parties shall retain the books and
      records for each quarterly period for ******* years after the submission
      of the corresponding report under clause 6.1 hereof or such shorter time
      as may be required by applicable law. Upon thirty (30) days prior notice,
      each Party (the "Audited Party") shall make its books and records
      available to

                                      18
<PAGE>

      independent accountants selected by the other Party (the "Auditing
      Party"), which accountants are reasonably acceptable to the Audited Party
      and have entered into a reasonable confidentiality agreement with the
      Audited Party, to conduct a review or audit once per calendar year, for
      the sole purpose of verifying the accuracy of the Audited Party's payments
      in compliance with this Agreement. The accounting firm shall report to the
      Auditing Party only whether there has been a royalty underpayment and, if
      so, the amount thereof.

7.    PATENT PROSECUTION AND ENFORCEMENT

7.1   Treatment of Project Technology.  MAXYGEN will have the sole discretion to
      decide which of the Project Technology will be:

      (a)   retained as its Confidential Information; or

      (b)   included in any patent application or other application for
            registered Intellectual Property Rights.

7.2   Filing of Patents.  If MAXYGEN decides that the Project Technology or any
      part of it will be included in any patent application or other application
      for registered Intellectual Property Rights protection, the application
      will be made by MAXYGEN in its own name and at its cost. TRPL will, at
      MAXYGEN's cost, render such assistance as MAXYGEN reasonably requires in
      the preparation, filing and prosecution of the patent.

7.3   Notice.  Each Party will give the other prompt notice of:

      (a)   any claim or allegation that the exercise of the rights under this
            Agreement constitute an infringement of the rights of any Third
            Party; and

      (b)   any Third Party's infringement or threatened infringement of a
            Party's Intellectual Property Rights in and to Project Technology
            (including without limitation, copyright, design and patent rights),
            of which it becomes aware.

7.4   Enforcement.  If either Party hereto becomes aware that any Intellectual
      Property Rights in and to Project Technology are being or have been
      infringed by any Third Party, such party shall promptly notify the other
      Party in writing describing the facts relating thereto in reasonable
      detail. MAXYGEN shall have the initial right, but not the obligation, to
      institute, prosecute and control any action, suit or proceeding with
      respect to such infringement, including any declaratory judgment action
      (each an "Action"), at its expense; using counsel of its choice. In the
      event that TRPL has exclusive rights to Project Technology in the TRPL
      Field pursuant to clause 5.2 and/or clause 5.3 and MAXYGEN fails to
      initiate or defend any Action involving an infringement that is within the
      scope of such exclusive rights of TRPL within ******* months of receiving
      notice of any infringement, TRPL shall have the right, but not the
      obligation, to initiate and control such an Action, at its expense. In any
      such event, TRPL shall promptly give MAXYGEN written notice thereof, and
      MAXYGEN shall cooperate reasonably with TRPL in connection with any such
      Action, at TRPL's expense; including without limitation, by joining such
      Action as a party if requested by TRPL. Any amounts

                                      19
<PAGE>

      recovered by TRPL in such an Action in excess of amounts paid to reimburse
      MAXYGEN and amounts expended by TRPL for the expenses incurred in
      connection with such Action, shall be *******.

7.5   In the event that TRPL has exclusive rights to Project Technology in the
      TRPL Field pursuant to clause 5.2 and/or 5.3, MAXYGEN will keep TRPL
      reasonably informed regarding any Action as described in clause 7.4
      instituted by MAXYGEN with respect to infringement within the TRPL Field.

8.    INDEPENDENT RESEARCH

8.1   Independent Research.  Subject to clauses 2.3(b), 2.12 and 12.4, each
      Party is entitled to conduct research outside of the Project free of any
      obligation to the other Party. Neither Party will have any obligation to
      conduct any research in the Project except as expressly described in the
      Project Plan.

8.2   No Reverse Engineering.  Except as expressly provided in this Agreement or
      other express written agreement between MAXYGEN and TRPL, TRPL shall not,
      and shall not authorize a RIO TINTO Group Member to, develop or
      commercialize, or authorize the development or commercialization of, or
      Exploit any process or product utilizing in any way any Gene Variant or
      Shuffled Gene, or any gene (or genetic element) which is based on or
      derived from any Gene Variant or Shuffled Gene, regardless of whether such
      gene (or genetic element) is made or obtained through synthesis, or
      mutation of a starting gene (or genetic element), or any product derived
      therefrom which contains or is made with the use of such a gene (or
      genetic element) or a Gene Variant or Shuffled Gene, or protein expressed
      from any of the foregoing. Except pursuant to a further written agreement
      between MAXYGEN and TRPL, TRPL will not itself, or through any Third
      Party, use any Project Technology and/or Improvements or structure-
      function data relating to any Gene Variants, including without limitation,
      consensus sequences or structural motifs, to reverse engineer,
      reconstruct, synthesize or otherwise modify or copy any Gene Variant or
      Shuffled Gene or any other gene or product with similar biological
      activities, or to attempt the same.

9.    CONFIDENTIALITY

9.1   Confidential Information.  Except as expressly provided herein, the
      Parties agree that the receiving Party will keep completely confidential
      and will not publish or otherwise disclose and will not use for any
      purpose except for the purposes contemplated by this Agreement any
      Confidential Information of the other Party (the "Disclosing Party")
      furnished to it by the Disclosing Party pursuant to this Agreement.
      Project Technology shall be deemed Confidential Information of MAXYGEN. In
      addition, except as expressly provided herein or to comply with applicable
      law, regulation or the order of a court of competent jurisdiction, the
      Parties agree that each Party will keep completely confidential and will
      not publish or otherwise disclose the terms of this Agreement.

                                      20
<PAGE>

9.2   Permitted Disclosures.  Confidential Information and/or the terms of this
      Agreement may be disclosed:

      (a)   to employees, agents, consultants and actual or bona fide potential
            Sublicensees of the non-Disclosing Party or its Affiliates (in the
            case of MAXYGEN) or of RIO TINTO Group Members (in the case of
            TRPL), but only to the extent reasonably required to accomplish the
            purposes of this Agreement and only if the non-Disclosing Party
            obtains prior written agreement from such employees, agents,
            consultants and actual or bona fide potential Sublicensees of the
            non-Disclosing Party or its Affiliates (in the case of MAXYGEN) or
            of RIO TINTO Group Members (in the case of TRPL) to whom disclosure
            is to be made to hold in confidence and not make use of such
            information for any purpose other than those permitted by this
            Agreement. Each Party will use at least the same standard of care as
            it uses to protect proprietary or confidential information of its
            own to ensure that such employees, agents and consultants do not
            disclose or make any unauthorized use of the Confidential
            Information; and

      (b)   to the extent reasonably necessary in prosecuting or defending
            litigation, complying with applicable governmental regulations, laws
            or court orders, or otherwise submitting required information to tax
            or other governmental authorities; provided that, if a Party is
            required to make any such disclosure of the terms of this Agreement
            or the other Party's Confidential Information, it will give
            reasonable advance notice to the other Party of such disclosure and,
            will use its reasonable efforts to secure confidential treatment of
            such Confidential Information (whether through protective orders or
            otherwise).

10.   PUBLIC STATEMENTS AND PUBLICATION

10.1  Use of Names.  Except to the extent required to comply with the law or a
      court order, neither Party will use the name or logo of the other Party
      without its written consent. In no event will either Party knowingly make
      any inaccurate or misleading statement concerning the other Party or the
      Project.

10.2  No Prejudice.  Subject to the provisions of clause 10.3, the Parties will
      use their reasonable efforts to ensure nothing is done which might
      prejudice the subsistence or Exploitation of the Project Technology or
      which would preclude the grant of a patent or cause the loss of
      Intellectual Property Rights protection. The Parties agree and acknowledge
      that this clause 10 is subject to the obligations of confidentiality
      contained in clause 9.

10.3  Publicity.  All publicity, press releases and other announcements relating
      to this Agreement and/or the Project will be reviewed in advance by, and
      will be subject to the approval of, both Parties; provided, approval shall
      be deemed to have been given if the reviewing Party does not respond
      within seven (7) days. Notwithstanding the foregoing, either Party may,
      without review or approval of the other Party, (i) publicize the existence
      and general subject matter of this Agreement without the other Party's
      approval, and (ii) disclose the terms of this Agreement to the extent
      required to comply with applicable

                                      21
<PAGE>

      securities laws. The Parties agree to release within ten (10) days after
      the Project Commencement Date a joint press release in an agreed form.
      Once a particular disclosure has been approved for disclosure, either
      Party may make disclosures which do not differ materially from it
      following review and approval by the other Party; provided, such approval
      shall be deemed to have been given if the reviewing Party does not respond
      within two (2) working days of the reviewing Party having received the
      material for review and approval.

10.4  Publication. The Parties (through their Management Committee members for
      so long as it exists, and afterward through such representatives as each
      Party may designate) will cooperate in appropriate publication of the
      results of research and development work performed pursuant to this
      Agreement, but subject to the predominating interest to obtain patent
      protection for any patentable subject matter. To this end, it is agreed
      that prior to any public disclosure of such results, the Party proposing
      disclosure will send the representatives of the other Party described
      above a copy of the information to be disclosed, and will allow the other
      Party thirty (30) days from the date of receipt in which to determine
      whether the information to be disclosed contains subject matter for which
      patent protection should be sought prior to disclosure, or otherwise
      contains Confidential Information of the reviewing Party which such Party
      desires to maintain as a trade secret. If notification is not received
      during the thirty (30) day period, the Party proposing disclosure will be
      free to proceed with the disclosure. If due to a valid business reason or
      a reasonable belief by the non-disclosing Party that the disclosure
      contains (i) Confidential Information of the non-disclosing Party, or (ii)
      subject matter for which a patentable invention should be sought, then
      prior to the expiration of the thirty (30) day period, the non-disclosing
      Party will so notify the representative of the disclosing Party, and the
      disclosing Party will then (a) at the request of the non-disclosing Party
      delete any Confidential Information of the non-disclosing Party, and/or
      (b) delay public disclosure for an additional period of up to sixty (60)
      days to permit the preparation and filing of a patent application on the
      subject matter to be disclosed or other protective action to be taken. The
      determination of authorship for any paper will be in accordance with
      accepted scientific practice.

11.   LIMITATION OF LIABILITY

      Subject to the provisions of clause 12 and clause 13, each Party will
      carry out the Project and use the other Party's Background Technology at
      its own risk. To the full extent permitted at law each Party excludes all
      warranties applicable to the Project, the Project Technology, and its
      Background Technology. Where under law any warranty cannot be excluded,
      each Party's liability is, at the option of the other Party, limited to
      the reperformance of its Contributions to the Project or the payment of
      the cost of having its Contributions to the Projects performed again. TO
      THE FULL EXTENT LAWFUL, NEITHER PARTY IS LIABLE TO THE OTHER PARTY FOR ANY
      SPECIAL, INDIRECT OR CONSEQUENTIAL DAMAGES ARISING UNDER OR PURSUANT TO
      THIS AGREEMENT, WHETHER IN RESPECT OF ITS NEGLIGENCE OR OTHER DEFAULT, OR
      OTHERWISE.

                                      22
<PAGE>

12.   REPRESENTATIONS AND WARRANTIES

12.1  Each Party represents and warrants to the other that it has the legal
      power, authority and right to enter into this Agreement and to perform its
      respective obligations set forth herein.

12.2  Each Party represents and warrants that as of the Effective Date of this
      Agreement it is not a Party to any agreement or arrangement with any Third
      Party or under any obligation or restriction, including pursuant to its
      certificate of incorporation or bylaws or rules, which in any way limits
      or conflicts with its ability to fulfill any of its obligations under this
      Agreement, and will not enter into any such agreement during the term of
      this Agreement.

12.3  Each Party represents and warrants that, to the best of its belief as of
      the Effective Date of this Agreement, there are no actions, suits,
      investigations, claims or proceedings pending or threatened in any way
      relating to its Background Technology.

12.4  MAXYGEN warrants to TRPL that it has not and will not during the period
      the Project is being conducted enter into any arrangement or understanding
      with any Third Party which arrangement or understanding requires MAXYGEN
      or any of its Affiliates, to provide Material or to conduct any project
      for the primary purpose of using Shuffling Technology for *******.
      Notwithstanding the above, it is understood and agreed that MAXYGEN shall
      have the right, at all times, to provide Material or conduct any projects
      alone or with Third Parties (a) where the primary purpose of such
      activities is *******.

12.5  Subject to clauses 12.3 and 12.4, MAXYGEN and TRPL each specifically
      disclaim that the Project will be successful, in whole or part or that any
      activities undertaken by one or both of them with respect to the Project
      will be successful. MAXYGEN AND TRPL EXPRESSLY DISCLAIM ANY WARRANTIES OR
      CONDITIONS, EXPRESS, IMPLIED, STATUTORY OR OTHERWISE, WITH RESPECT TO THE
      CONFIDENTIAL INFORMATION, INTELLECTUAL PROPERTY RIGHTS OF SUCH PARTY
      INCLUDING WITHOUT LIMITATION, PATENTS OR KNOW-HOW, MATERIALS,
      IMPROVEMENTS, SHUFFLING TECHNOLOGY, PROGRAM TECHNOLOGY, GENE(S), GENE
      VARIANT(S), OR SHUFFLED GENE(S), INCLUDING, WITHOUT LIMITATION, ANY
      WARRANTY OF MERCHANTABILITY, OR FITNESS FOR A PARTICULAR PURPOSE, VALIDITY
      OF ANY SHUFFLING TECHNOLOGY OR PROJECT TECHNOLOGY, PATENTED OR UNPATENTED,
      OR NON-INFRINGEMENT OF THE INTELLECTUAL PROPERTY RIGHTS OF THIRD PARTIES.

13.   INDEMNIFICATION AND INSURANCE

13.1  MAXYGEN.  MAXYGEN will indemnify, defend and hold harmless TRPL and its
      officers, employees and agents from and against any and all Third Party
      actions, claims, demands, costs, liabilities or expenses (including actual
      legal costs) (each a "Liability") made, sustained, brought or prosecuted
      or in any manner based upon, occasioned by or attributable to any injury
      to any person (including death) or loss of or damage to property

                                      23
<PAGE>

      which may arise from or as a direct result of MAXYGEN's conduct of
      activities in connection with the Project; except, in each case, to the
      extent due to the negligence or willful misconduct of TRPL.
      Notwithstanding the above, the foregoing obligations shall not apply to
      any Liability arising out of or in connection with the use of any
      particular Gene or Shuffled Gene in the Project.

13.2  TRPL.  TRPL will indemnify, defend and hold harmless MAXYGEN and its
      officers, employees and agents from and against any and all Third Party
      actions, claims, demands, costs, liabilities or expenses (including actual
      legal costs) (each a "Liability") made, sustained, brought or prosecuted
      or in any manner based upon, occasioned by or attributable to any injury
      to any person (including death) or loss of or damage to property which may
      arise from or as a direct result of TRPL's conduct of activities in
      connection with the Project; except, in each case, to the extent due to
      the negligence or willful misconduct of MAXYGEN.

13.3  Insurance.  Each Party will procure adequate insurances such as are
      customary and appropriate in their industry, including product liability
      insurance at the time of Exploitation by such Party, and Third Party
      liability insurance in respect of its participation in the Project and its
      use and permitted Exploitation of the Background Technology and Project
      Technology. Each such insurance policy held by MAXYGEN and TRPL will note
      the other Party's interest as a named insured under the policy and include
      a waiver of the insurers' right of subrogation against the other Party.
      Each Party will, on the request of the other Party, produce evidence of
      the currency of the insurance policies referred to in this clause 13. Each
      Party undertakes at all times to comply with the terms of its insurance
      policies the subject of clause 13.

14.   TERM AND TERMINATION

14.1  Term.  The initial term of this Agreement will commence on the Effective
      Date, and, unless terminated earlier as provided in this clause 14,
      continue in full force and effect on a country-by-country and Product-by-
      Product basis until there are no remaining payment obligations for such
      Product in such country.

14.2  Termination for Breach.  A Party may terminate this Agreement and the
      Project by notice in writing to the other Party on the happening of one or
      more of the following:

      (a)   if a Party commits a material breach or default of any of the terms
            and conditions contained herein, and does not within sixty (60) days
            of receipt of notice in writing from the other Party requiring the
            breach to be remedied cure the breach within such time; or

      (b)   if a material warranty, representation or statement given or made by
            a Party in this Agreement is not complied with or proves to be
            untrue and is not otherwise compensable in an award of damages.

14.3  Termination by Mutual Agreement.  The Parties may terminate this Agreement
      by written mutual agreement. In the event that such termination occurs
      during the conduct of the Project, the Parties shall negotiate bona fide
      in good faith an orderly and

                                      24
<PAGE>

      reasonably prompt wind-down of the Project and the associated funding
      obligations of TRPL.

14.4  Termination for Insolvency.  TRPL may, in its sole discretion, terminate
      this Agreement (together with the Project, if such termination is during
      the Project Term) by providing MAXYGEN with written notice on the
      happening of any of the following events:

      (a)   if MAXYGEN is the subject of winding up or liquidation proceedings,
            whether voluntary or compulsory, otherwise than for the purpose of
            and followed by, a reconstruction, amalgamation or reorganization;

      (b)   if MAXYGEN has become insolvent, bankrupt or is subject to the
            appointment of a mortgagee, a receiver or manager or an inspector to
            investigate its affairs, enters into any arrangement or composition
            with its creditors generally, or is unable to pay its debts as and
            when they become due;

      (c)   if execution is levied upon all or any part of the assets of
            MAXYGEN, provided that no breach will take place hereunder if the
            execution is contested in good faith or if within thirty (30) days
            after it is levied payment is made in full to the judgment creditor
            in question of all amounts owing to such judgment creditor,

      such termination to be effective immediately upon receipt of the above
      mentioned written notice. In the event of termination of this Agreement by
      TRPL pursuant to this clause 14.4 during Phase I and/or the Phase II
      Negotiation Period described in clause 2.3, MAXYGEN shall grant to TRPL
      the licenses described in clause 5.2(a), which license shall be subject to
      the sharing of Revenues as set forth in clause 5.2(c).

14.5  Effect of Termination.

      (a)   Accrued Obligations.  Termination of this Agreement for any reason
            will not release either Party hereto from any liability which, at
            the time of such termination, has already accrued to the other Party
            or which is attributable to a period prior to such termination nor
            preclude either Party from pursuing all rights and remedies it may
            have at law or in equity with respect to any breach of this
            Agreement.

      (b)   Return of Confidential Information and Background Technology.  Upon
            termination of this Agreement, TRPL and MAXYGEN will each promptly
            return to the other Party all Confidential Information received from
            the other Party (except one copy of which may be retained by legal
            counsel for archival purposes and ensuring compliance with clause
            9), and all MAXYGEN Background Technology will be returned to
            MAXYGEN.

      (c)   Sublicenses.  Upon termination of this Agreement, any sublicenses
            granted by each Party shall remain in force and effect and shall be
            assigned by the Party granting such sublicense (the "Sublicensing
            Party") to the other Party, provided, however, that the financial
            obligations of each Sublicensee to the non-

                                      25
<PAGE>

            Sublicensing Party shall be limited to the amounts the Sublicensing
            Party would have been obligated to pay to non-Sublicensing Party for
            the activities of such Sublicensee pursuant to this Agreement.

      (d)   Stock on Hand.  In the event this Agreement is terminated for any
            reason after the first commercial sale of one or more Products by a
            Party, such Party and its Sublicensees and its Affiliates (in the
            case of MAXYGEN) and RIO TINTO Group Members (in the case of TRPL)
            shall have right to sell or otherwise dispose of the stock of any
            such Product then on hand, subject to all applicable revenue sharing
            or other payment obligations.

      (e)   Licenses.

            (i)   In the event of any termination by MAXYGEN pursuant to clause
                  14.2(a) for TRPL's failure to make Revenue sharing payments
                  due under clause 5.2(c), the licenses, if any, granted to TRPL
                  pursuant to clause 5.2(a) shall terminate concurrently.

            (ii)  In the event of any termination by TRPL pursuant to clause
                  14.2(a) for MAXYGEN's failure to make Revenue sharing payments
                  due under clause 5.2(c), the licenses, if any, granted to
                  MAXYGEN pursuant to clause 5.2(a) shall terminate
                  concurrently. In the event of any termination by TRPL pursuant
                  to clause 14.4, the licenses, if any, granted to MAXYGEN
                  pursuant to clause 5.2(b) shall terminate concurrently.

            (iii) Except as provided in this clause 14.5(e), the licenses and
                  rights granted to the Parties under this Agreement in effect
                  at the effective date of such termination shall survive;
                  provided, nothing in this clause 14.5(e) shall prohibit, or be
                  construed to prohibit, the later termination of such a
                  surviving license in accordance with clause 14.2(a) and/or
                  14.4 and this clause 14.5(e).

      (f)   Liquidated Damages.  If MAXYGEN terminates this Agreement pursuant
            to clause 14.2 during Phase II of the Project, then TRPL shall pay
            to MAXYGEN as liquidated damages for the failure to pay such amount,
            *******. The payment of such amount shall not limit MAXYGEN's right
            to seek or obtain any other remedies available to it at law or in
            equity.

14.6  Survival.  The provisions of clauses 2.9, 4.1, 4.4, 4.5, 5.1, 5.2(c),
      5.2(d), 5.2(e), 5.2(f), 6, 7.1, 7.2, 7.3, 8, 9, 10, 11, 12.5, 13.1, 13.2,
      14.5, 14.6, 15, 16, 21, 22, 23 and 25 will survive the expiration or
      termination of this Agreement for any reason.

15.   GOVERNING LAW

      This Agreement and any dispute arising from the performance or any breach
      of it, including without limitation, any arbitration, will be governed by
      and construed in accordance with the laws of the State of California.
      without reference to conflicts of laws

                                      26
<PAGE>

      principles. Each Party submits to the jurisdiction of the federal and
      state courts in, and for, the State of California and the courts of appeal
      therefrom.

16.   ASSIGNMENT

      This Agreement will not be assigned by either Party to any third Party
      hereto without the written consent of the other Party, and any purported
      assignment prohibited by this provision shall be null and void; except
      either Party may assign this Agreement, without such consent, to (i) an
      Affiliate, in the case of MAXYGEN, or to a RIO TINTO Group Member, in the
      case of TRPL; or (ii) an entity that acquires all or substantially all of
      the business or assets of such Party to which this Agreement pertains,
      whether by merger, reorganization, acquisition, sale or otherwise. The
      terms and conditions of this Agreement shall be binding on and inure to
      the benefit of the permitted successors and assigns of the Parties.

17.   SEVERABILITY

      Each word, phrase, sentence, paragraph, section, clause and subclause ("a
      provision") of this Agreement is severable and if a court determines that
      a provision is unenforceable, illegal or void then the court may sever
      that provision without affecting the validity of the other provisions of
      this Agreement.

18.   WAIVER

      The failure by TRPL or MAXYGEN to exercise or delay in exercising a power
      or right does not operate as a waiver of that power or right. The exercise
      of a power or right does not preclude its future exercise or the exercise
      of any other power or right.

19.   AMENDMENT

      This Agreement can only be amended by written agreement between the
      Parties.

20.   NOTICES

      Any notice required or permitted by this Agreement will be in writing and
      will be sent by prepaid registered or certified mail, return receipt
      requested, internationally recognized courier or personal delivery, or by
      fax with confirming letter mailed under the conditions described above in
      each case addressed to the other party at the address shown below or at
      such other address for which such party gives notice hereunder. Such
      notice will be deemed to have been given when delivered:

                  If to MAXYGEN:  Maxygen, Inc.
                                  515 Galveston Drive
                                  Redwood City, CA  94063
                                  Attn: Chief Executive Officer

                                      27
<PAGE>

                  If to TRPL:     Technological Resources Pty Limited
                                  55 Collins Street
                                  South Melbourne
                                  Victoria 3000
                                  Attn: General Manager Commercial
21.   ENTIRE AGREEMENT

      This Agreement, together with its Schedules, which are hereby incorporated
      by reference, contains the whole agreement of the Parties relating to its
      subject matter and it supersedes any and all agreements, understandings or
      commitments in connection with the same subject matter.

22.   RELATIONSHIP

      The Parties agree that this document does not create or evidence a
      relationship between them of joint venture, partnership, employer and
      employee or principal and agent.

23.   DISPUTE RESOLUTION

23.1  Senior Executives.  The Parties agree to co-operate and to use all
      reasonable endeavors to resolve any disputes or differences between them.
      Disputes between the Parties representative on the Management Committee
      which remain unresolved for thirty (30) days will be referred to the Chief
      Executive Officer in the case of MAXYGEN and the Managing Director-
      Research & Technology, in the case of TRPL, for resolution.

23.2  Mediation.  If a dispute arises out of or relates to this Agreement, or
      the breach of it, and if said dispute cannot be settled through
      negotiation, the parties agree first to try in good faith to settle the
      dispute by non-binding mediation under the appropriate rules, if any, for
      such mediation under the rules of the International Chamber of Commerce
      ("ICC") or, if there are no such rules at the time of such mediation,
      under the Commercial Mediation Rules of the American Arbitration
      Association, before resorting to arbitration, or some other dispute
      resolution procedures.

23.3  Arbitration.  If the Parties are unable to resolve any dispute,
      controversy or claim between them arising out of or relating to the
      validity, construction, enforceability or performance of this Agreement,
      including disputes relating to alleged breach or to termination of this
      Agreement (each, a "Dispute"), the Dispute will be finally settled by
      binding arbitration conducted pursuant to the applicable rules of the ICC
      then in effect by one (1) arbitrator appointed in accordance with such
      rules. The arbitration shall take place in Melbourne, Australia, if
      initiated by MAXYGEN, and in Palo Alto, California, if initiated by TRPL.
      The arbitrator will determine what discovery will be permitted, consistent
      with the goal of limiting the cost and time which the parties will expend
      for discovery; provided the arbitrator will permit such discovery as they
      deem necessary to permit an equitable resolution of the dispute; provided,
      the arbitrator shall not order or permit discovery against one Party of a
      type and scope such Party cannot obtain against the other Party for use in
      the arbitration as a result of the laws of the country of residence of the
      other Party. The costs of any arbitration, including administrative fees
      and fees of

                                      28
<PAGE>

      the arbitrator, will be shared equally by the Parties. Each Party will
      bear the cost of its own attorneys' fees and expert fees. The decision
      and/or award rendered by the arbitrator will be written (specifically
      stating the arbitrator's findings of facts as well as the reasons upon
      which the arbitrator's decision is based), final and non-appealable
      (except for an alleged act of corruption or fraud on the part of the
      arbitrator) and may be entered in any court of competent jurisdiction. The
      Parties agree that, any provision of applicable law notwithstanding, they
      will not request, and the arbitrator will have no authority to award,
      punitive or exemplary damages against any Party. The arbitrator will have
      the authority to grant injunctive relief and order specific performance.
      The Parties and the arbitrator will use their best efforts to complete any
      such arbitration within one (1) year, unless a Party can demonstrate to
      the arbitrator that the complexity of the issues or other reasons warrant
      the extension of the time table. In such case, the arbitrator may extend
      such time table as reasonably required. The arbitrator will, in rendering
      its decision, apply the substantive law of the State of California,
      without regard to its conflict of laws provisions.

23.4  Interlocutory Relief.  Compliance with this clause 23 is a condition
      precedent to seeking relief in any court or tribunal in respect of a
      dispute, but nothing in this clause 23 will prevent a Party from seeking
      interlocutory relief in courts of appropriate jurisdiction, pending the
      establishment of the arbitral tribunal or pending the arbitral tribunal's
      determination of the merits of the controversy, if necessary to protect
      the Confidential Information, rights or property of that Party.

24.   FORCE MAJEURE

      Neither Party will be liable for any failure to carry out its obligations
      under this Agreement where such failure is due to any cause beyond the
      reasonable control of such party.

25.   MISCELLANEOUS

25.1  Advice of Counsel.  MAXYGEN and TRPL have each consulted counsel of their
      choice regarding this Agreement, and each acknowledges and agrees that
      this Agreement will not be deemed to have been drafted by one Party or
      another and will be construed accordingly.

25.2  Further Assurances.  At any time or from time to time on and after the
      date of this Agreement, either Party will at the request of the other
      Party (i) deliver to the requesting Party such records, data or other
      documents consistent with the provisions of this Agreement, (ii) execute,
      and deliver or cause to be delivered, all such consents, documents or
      further instruments of assignment, transfer or license, and (iii) take or
      cause to be taken all such actions, as the requesting Party may reasonably
      deem necessary or desirable in order for the requesting Party to obtain
      the full benefits of this Agreement.

25.3  Compliance with Laws.  Each Party will furnish to the other Party any
      information requested or required by that Party during the term of this
      Agreement or any extension of it to enable that Party to comply with the
      requirements of any federal, state or

                                      29
<PAGE>

      government agency. Each Party will comply with all applicable U.S. and
      Australian state, regional and local laws, rules and regulations relating
      to its activities to be performed pursuant to this Agreement, and will
      obtain, at its own expense, all necessary approvals, consents and permits
      required by the applicable agencies of the government of the United States
      and foreign jurisdictions.

25.4  Headings.  The captions to the several clauses and subclauses are not a
      part of this Agreement, but are included for convenience of reference only
      and will not affect its meaning or interpretation.

25.5  Binding Effect.  This Agreement will be binding upon and inure to the
      benefit of the parties and their respective legal representatives,
      successors and permitted assigns.

25.6  Counterparts.  This Agreement may be executed in two counterparts, each of
      which will be deemed an original and which together will constitute one
      instrument.

25.7  Business Unit.  The obligations of TRPL under this Agreement are
      obligations of the Business Unit and MAXYGEN acknowledges that nothing in
      this Agreement binds any other Business Unit of TRPL in so far as the
      obligations of TRPL relate to the conduct of the Project.

25.8  Performance Warranty.  Notwithstanding clause 25.7, TRPL and MAXYGEN
      hereby respectively warrant and guarantee the performance of any and all
      rights and obligations of this Agreement by their Sublicensees and
      Affiliates, in the case of MAXYGEN, and RIO TINTO Group Members, in the
      case of TRPL.

                                      30
<PAGE>

EXECUTED BY THE PARTIES AS AN AGREEMENT

Signed for and on behalf of             )
TECHNOLOGICAL                           )
RESOURCES PTY LIMITED                   )
                                        )
By R. Batterham                         )  /s/ R. Batterham
  -----------------------------------   )
(print name)                            )
                                        )
Chief Technologist                      )
- -------------------------------------   )
Title                                   )
                                        )
                                        )
a duly authorized officer of TRPL       )
and in the presence of:                 )
                                        )
   J. M. Elliott                        ) /s/ J. M. Elliott
- -------------------------------------   )
Witness                                 )
                                        )
                                        )
Signed for and on behalf of             )
MAXYGEN INC.                            )
                                        )
                                        )
By /s/ Russell Howard                   )
  -----------------------------------   )
   Russell Howard                       )
   Chief Executive Officer              )
                                        )
                                        )
a duly authorized officer of            )
MAXYGEN INC.                            )
and in the presence of:                 )
                                        )
   /s/ Michael Rabson                   )
- -------------------------------------   )
Witness                                 )

                                      31

<PAGE>

                                                                   EXHIBIT 10.16

January 28, 2000


Joseph A. Affholter, Ph.D.
17440 Lakeview Drive
Morgan Hill, CA 95037

Re:  Separation from Employment

Dear Joe:

     This letter, upon your signature, will constitute the agreement between you
and Maxygen, Inc. on the terms of your separation from employment with Maxygen.

     1.       Your employment with Maxygen will end effective January 28, 2000.

     2.       You will be paid your base salary through the effective date of
your separation, plus all accrued and unused FTO time, less customary payroll
deductions.

     3.       Within thirty days of your separation, you will return to Maxygen
any and all information and materials you have that are or relate to Maxygen's
Confidential Information, as that term is defined in the Confidential
Information, Secrecy and Inventions Agreement you signed with Maxygen on April
29, 1998 (the "CI Agreement"), whether in hard copy, electronic form or in any
other format. You further agree to continue to be bound by the terms of the CI
Agreement.

              Notwithstanding the foregoing, it is understood that, by virtue of
your former employment with Maxygen and your ongoing consultancy with Maxygen as
described below, you will continue to have in your possession Confidential
Information of Maxygen. You agree to treat such information as provided in the
CI Agreement.

     4.       Upon approval of the Maxygen Board of Directors, Maxygen agrees to
accelerate the vesting of 20,675 stock options granted to you on June 19, 1998,
under the terms of the Maxygen 1997 Stock Option Plan.  Those shares will vest
as of your separation date at an exercise price of $0.30 per share.  An
additional 6,875 stock options granted to you on June 19, 1998, under the terms
of the Maxygen 1997 Stock Option Plan will vest on June 30, 2001, pursuant to
the terms of the Exclusive Consulting Agreement attached hereto ("the Consulting
Agreement"), which you agree to sign and which is incorporated into this letter
by this reference.  Except as provided in this Paragraph 4, Paragraph 5 below
and the Exclusive Consulting Agreement, all other non-vested Maxygen stock
options granted to you will be cancelled as of your separation date.
<PAGE>

Joseph A. Affholter
January 28, 2000
Page 2

     5.       Maxygen also agrees that you will continue to be eligible to
participate in the Maxygen Bonus Plan for 1998-1999, as follows.  Maxygen
acknowledges that you currently have 16,875 unvested Incentive Stock Options in
the bonus plan at an exercise price of $0.75.  The Board, in its sole
discretion, has the right to determine whether to approve accelerated vesting of
a percentage of unvested bonus options for the members of Maxygen's senior
management team.  Maxygen agrees that if the Board approves accelerated vesting
of a percentage of bonus shares for other members of Maxygen's senior management
team, you will receive accelerating of the same percentage under the same terms.
Any additional unvested shares remaining in the bonus plan for which the Board
does not approve accelerated vesting will be forfeited as of your separation
date.

     6.       Within 10 business days following the execution of this letter
and the Consulting Agreement, Maxygen agrees to provide you with a mutually
acceptable letter of recommendation from the President and Chief Executive
Officer of Maxygen focusing on your professional strengths and contributions
to Maxygen.  Maxygen also agrees to work with you to develop a mutually
acceptable public statement describing your departure from Maxygen. You agree
to direct any questions regarding the reasons for your separation from Maxygen
to the Vice President, Human Resources of Maxygen. On behalf of Maxygen, we
will respond by stating only your dates of employment and job title and by
reiterating information contained in the letter. Maxygen agrees to keep
confidential all other aspects of the reasons for your separation from
employment with Maxygen.

     7.       Maxygen further agrees to modify the housing loans provided to
you by Maxygen in March 1998 and April 1999 (which loans currently have a total
outstanding principal balance of $150,000), to a personal loan for $150,000,
with interest calculated semi-annually from February 1, 2001 at 5.59%, and to
defer payment of such loan until April 1, 2003 with respect to $72,500 of the
principal and until March 30, 2004 with respect to $77,500 of the principal. You
agree that the personal loan will be secured by a pledge of vested shares of
Maxygen stock valued at $300,000 as of the date your loans are converted, upon
your execution of the loan documents attached hereto. Maxygen further to defer
repayment of the loan provided to you in connection with your early exercise of
Incentive Stock Options on October 9, 1999 to June 30, 2002, provided that the
Consulting Agreement has not been terminated before June 30, 2001 (a) for cause
by Maxygen, or (b) for any reason by you.

     8.       In consideration of all the above, you, for yourself, your
representatives, heirs, successors and assigns, waive and release and promise
never to assert any and all claims that you have or might have as of the date
you sign this letter, whether known or unknown, against Maxygen, and its current
and former officers, directors, shareholders, agents, attorneys, employees,
successors, assigns, parents, affiliates and subsidiaries, arising from or
related to your employment with Maxygen, and/or the termination of your
employment with Maxygen.
<PAGE>

Joseph A. Affholter
January 28, 2000
Page 3

               These claims include, but are not limited to, claims arising
under federal, state and local statutory or common law, such as Title VII of
the Civil Rights Act of 1964, the Age Discrimination in Employment Act, the
Americans with Disabilities Act, the Family and Medical Leave Act, the
California Fair Employment and Housing Act, the California Family Rights Act,
and the law of contract and tort.

     9.        You, for yourself, your representatives, heirs, successors and
assigns, waive, release and promise never to assert any such claims, even if
you do not believe that you presently have such claims. You therefore waive
your rights under section 1542 of the California Civil Code, which states:

          A general release does not extend to claims which the creditor
          does not know or suspect to exist in his favor at the time of
          executing the release, which if known to him must have materially
          affected his settlement with the debtor.

     10.       Unless required by law, you will use your best efforts not to
disclose to others any information regarding:

          (a) any Confidential Information of Maxygen, as that term is defined
          in the CI Agreement;

          (b) the terms and nature of this separation letter and the benefit
          being paid under it.  However, you may disclose this information to
          your spouse and immediate family, and to your attorney(s),
          accountant(s) or tax expert(s), investment or other advisor(s) to
          whom you believe you must make the disclosure in order for them to
          render professional services to you.  You will require them, however,
          to maintain the confidentiality of this information just as you must.

     11.       In the event that you breach any of your obligations under this
separation letter or as otherwise imposed by law, Maxygen will be entitled to
recover the benefit paid under the agreement and to obtain all other relief
provided by law or equity.  Notwithstanding the foregoing, in the event of any
breach of the provisions of Paragraph 10(b) above, Maxygen's ability to recover
the benefits paid to you under this letter will be reduced by 25% upon each
successive anniversary of the date on which you sign this letter.
<PAGE>

Joseph A. Affholter
January 28, 2000
Page 4

          Joe, I am pleased that we were able to end your employment with
Maxygen on these amicable terms.  Maxygen and I thank you for your service to
the Company and wish you every success in your future endeavors.

          Sincerely,

          /s/ Russell Howard

          Russell Howard
          President and Chief Executive Officer
          Maxygen, Inc.


By signing this letter, I acknowledge that I have had the opportunity to review
this separation letter carefully; that I have read and understand the terms of
the letter and that I voluntarily agree to them; and that I have been advised
that I may consult with an attorney prior to signing this letter and the release
contained herein.

                                     /s/ Joseph A. Affholter
Dated:  January 28, 2000.          __________________________
                                    Joseph A. Affholter, Ph.D.

<PAGE>

                                                                   EXHIBIT 10.17

                        EXCLUSIVE CONSULTING AGREEMENT
                        ------------------------------


     This Exclusive Consulting Agreement ("Agreement") entered into by and
between Maxygen, Inc. (hereinafter "Maxygen"), a Delaware corporation, and
Joseph A. Affholter, Ph.D. (hereinafter "Consultant"), an individual.

     In consideration of the promises set forth below, the parties agree as
follows.

     1.   Term of this Agreement.  This Agreement will be effective as of the
date set forth below and will continue in effect until June 30, 2001, unless it
is terminated in accordance with the provisions of Paragraph 8, below ("Contract
Term").

     2.   Services to be Performed by Consultant.  Consultant agrees to provide
those services specified in Exhibit A to this Agreement.  Written requests or
approvals for services to be conducted by Consultant under this Agreement may be
given by:  Maxygen's CEO, President, General Counsel, VP of Business
Development, Intellectual Property Counsel and/or chemical business management.
Such requests may be received by e-mail, fax or written letter.

     3.   Relationship of the Parties.

          a.  The parties intend to create an independent contractor and
principal relationship by this Agreement. Consultant will not represent himself
as an agent, employee, joint venturer or partner of Maxygen. Notwithstanding the
above, Maxygen acknowledges Consultant as an expert in the field of directed
molecular evolution and recognizes Consultant's right to use data in the public
domain (which Consultant does not otherwise have an obligation to maintain in
confidence) to highlight the relevance of directed molecular evolution
technologies in multiple industries.

          b.  The conduct and control of the work performed pursuant to this
Agreement will lie with Consultant.  However, Consultant will perform this work
at the specific direction (though not control) of Maxygen.

          c.  (i)   During the first six (6) months of the Contract Term,
subject to Consultant's obligations under Paragraph 7 of the Agreement,
Consultant may perform services for other clients, persons or companies as
Consultant sees fit, except that Consultant may not knowingly accept employment
with, perform services for, become a founder of, or engage in any conduct, role
or capacity in which the Consultant would provide to any business entity any
technical or business advice or information related to the development or use of
(x) technologies commonly referred to as "gene shuffling" or "molecular
breeding" in any format including, without limitation, single gene, gene family,
or whole genome-based formats, or (y) other novel methods for generating high-
quality genetic diversity via directed evolution of genetic materials.

              (ii)  During the portion of the Contract Term after the date six
(6) months from the start of the Contract Term, subject to Consultant's
obligations under Paragraph
<PAGE>

7 of the Agreement, Consultant may perform services for other clients, persons
or companies as Consultant sees fit, except that Consultant may not knowingly
accept employment with, perform services for, become a founder of, or engage in
any conduct, role or capacity in which the Consultant would provide to any
business entity any technical advice or information related to the development
or use of in vitro or in vivo recombination-based methods for directed molecular
          -- -----    -- ----
evolution, without limitation those commonly referred to as "gene shuffling" or
"molecular breeding," in any format; however, during such period Consultant may
(provided he does not disclose or use any Confidential Information of Maxygen)
provide advice regarding targets to which directed molecular evolution could be
applied to develop commercial products or processes, without providing technical
advice or information on how to accomplish the same.

              (iii) Notwithstanding Paragraphs 3.C(i) and (ii) above, Consultant
may (x) conduct the activities described therein (without any disclosure or use
of Maxygen Confidential Information) to the extent that Consultant can
reasonably demonstrate that he could have done so prior to his employment with
Maxygen, and (y) Consultant may comment generally on benefits of using Maxygen
technology by reference to information then within the public domain.

              (iv)  If during the Contract Term Consultant wishes to conduct any
activity which he believes may fall within the scope of the then-prohibited
activities described in Paragraphs 3.C(i) or (ii) above, he shall provide to
Maxygen notice describing in writing the activities he wishes to conduct, but
shall have no obligation to disclose to Maxygen the confidential information of
third parties.  Maxygen shall within ten (10) business days of receipt of such
notice and information notify Consultant in writing whether or not he may
conduct such activities for such third party; provided, such time period shall
not apply if the Consultant has failed to provide Maxygen sufficient detail
regarding the proposed activities to reasonably allow it to evaluate the impact
of Consultant's proposed activities on Maxygen.  In the event Maxygen declines
to permit Consultant to perform the proposed activities, it will summarize in
brief written form the basis for its denial and, where feasible, provide
positive guidance as to changes in the proposed activities which could make the
proposed activity acceptable, provided Maxygen has no obligation to approve any
activities which are not expressly permitted by Paragraphs 3.C(i) or (ii) above.
Unless agreed to otherwise by the Parties in writing, a failure of Maxygen to
provide a response within the specified 10 business day period, shall constitute
approval of the proposed activity.

     4.   Benefits.  Consultant will not be eligible for, nor will participate
in, any health, pension, or other employee benefit plan sponsored or established
by Maxygen for the benefit of its employees.

     5.   Billings.  Consultant agrees to submit to the Controller of Maxygen,
Inc., at 515 Galveston Drive, Redwood City, California 94063, by the tenth day
of each calendar month, in a form reasonably acceptable to Maxygen, a written
invoice or facsimile that sets forth (i) the number of hours worked by
Consultant each day, together with a detailed description of the services
performed, including time and expenses for agreed-upon travel, and (ii) the
total compensation owed for the month.
<PAGE>

     6.   Compensation to Consultant.  Maxygen will pay Consultant for services
requested by Maxygen and actually performed by Consultant, at the rate of $250
per hour, but in no event fewer than forty hours per month for the months of
February, March, April and May 2000, twenty-five hours per month for the months
of June and July 2000, and five hours per month thereafter for the remainder of
the Contract Term (the "Consulting Fees").  Consultant is not expected to be
available on an "on-call" basis, but will be available for business meetings and
travel at agreed-upon times, and will be given notice of upcoming travel and
Maxygen's consulting needs as far in advance as reasonably practical (generally
ten business days or more).  Nothing herein shall be interpreted as requiring
Consultant to provide more than the above-described minimum number of consulting
hours per month.  Maxygen agrees to make Payment no later than 30 days after
receipt of the invoice in the form described in Paragraph 5 above.  No payments
will be made to Consultant as reimbursement for travel and other business
expenses unless agreed in advance in writing by Maxygen.  In addition, upon
approval of the Board of Directors of Maxygen, on June 30, 2001, Maxygen will
vest in Consultant 6,875 Stock Options at an exercise price of $0.30, which
options otherwise would have vested had Consultant been an employee of Maxygen
on April 29, 2000, provided that this Agreement has not been terminated prior to
June 30, 2001 pursuant to Paragraph 8 of this Agreement either (i) for cause by
Maxygen, or (ii) for any reason by Consultant.  Consultant understands and
agrees that because of his separation from employment with Maxygen, his
continuing option will become a Non-statutory Option and will no longer be an
Incentive Stock Option.  Consultant further understands and agrees that the only
option that will continue to vest during the Contract Term will be for the
aforesaid 6,875 options.

     7.   Confidential Information.

          a.  Maxygen has and will develop, compile, and own certain proprietary
techniques and confidential information ("Confidential Information") that have
great value in its business.  Consultant acknowledges and agrees that
Confidential Information includes information Consultant learns or acquires in
connection with the performance of services under this Agreement.  Confidential
Information includes all information that has or could have commercial value or
other utility in the business in which Maxygen is engaged, or in which it
contemplates engaging, or that Maxygen has acquired in confidence from third
parties.  Confidential Information also includes all other non-public
information of Maxygen or third parties disclosed to Maxygen in confidence, the
unauthorized disclosure of which could be detrimental to the interests of
Maxygen, whether or not this information is identified as Confidential
Information.  Confidential Information also includes all information that
Consultant may have learned about Maxygen's business, operations or plans during
the negotiation of this Agreement or during his prior employment with Maxygen.
Confidential Information also includes all information defined as "Confidential
Information" in the Maxygen Confidential Information, Secrecy and Inventions
Agreement signed by Consultant on April 29, 1998 ("the CI Agreement").
Consultant agrees to continue to be bound by the CI Agreement, including but not
limited to the Inventions portion thereof, and acknowledges that the CI
Agreement remains in all respects valid and in force, throughout and after the
Contract Term.

          b.  By example and without limitation, Confidential Information
includes any and all information concerning Maxygen's research programs, product
development, biological materials, research methods, related products,
technology, inventions, patent applications, trade
<PAGE>

secrets or other products and any other information of value relating to the
business affairs and/or fields of interest of Maxygen, whether communicated
orally or in writing, including without limitation, concepts, techniques,
processes, designs, biological materials, methods for developing or identifying
novel products, software, databases, cost data, and other technical know-how,
financial, research, marketing and personnel information, and other business
information including information with respect to which Maxygen is under an
obligation of confidentiality with any third party. Confidential Information
does not include information: (i) generally known in the relevant trade or
industry; or (ii) known to and freely usable by Consultant before entering into
this Agreement with Maxygen; but Confidential Information shall not be deemed to
be generally known (x) merely because it is embraced by more general information
subject to the above, or (y) merely because it is published in general terms
without description of the specific Confidential Information subject to this
section.

          c.  Consultant acknowledges and agrees that Confidential Information
is proprietary, constitutes a valuable asset of Maxygen, and is the sole
property of Maxygen. Consultant agrees that at all times during and after the
Contract Term, he will hold in trust, keep confidential, and not disclose to any
third party, or make any use of, the Confidential Information of Maxygen, except
as is strictly required to perform services under this Agreement and with the
prior written approval of Maxygen. Consultant further agrees not to disclose, or
to cause the transmission, removal, or transport of, Confidential Information
from Maxygen's principal place of business at 515 Galveston Drive, Redwood City,
California 94063, or any other place of business; provided, Consultant may
communicate freely with Maxygen.

          d.  Consultant acknowledges that all documents, whether in hard copy,
electronic for or any other format, including, but not limited to, laboratory
and other notebooks, software, computer programs, tapes, printouts, records,
databases, manuals, letters, email messages, reports, blueprints, drawings,
customer lists, and other evidence of Confidential Information and other
information concerning the business, operation, or plans of Maxygen, including
copies, that come into the possession of Consultant, whether produced by
Consultant or others are and will remain the property of Maxygen, and will be
treated as Confidential Information.

          e.  Consultant acknowledges that the unauthorized use or disclosure of
Maxygen's Confidential Information by Consultant may lead to immediate
termination of this Agreement under Paragraph 8, and can lead to legal action by
Maxygen.

          f.  Notwithstanding the foregoing, it is understood that, by virtue of
his former employment with Maxygen and his ongoing consultancy with Maxygen
under this Agreement, Consultant will continue to have in his possession
Confidential Information of Maxygen. Consultant agrees to treat such information
as provided in the CI Agreement.

     8.   Termination of this Agreement.

          a.  On Written Notice. Either party may terminate this Agreement,
without cause, by giving thirty (30) days' notice to the other party. In the
event of such termination, the parties agree to act toward each other in good
faith during the notice period. In the event of such termination by Maxygen, the
stock options referred to in Paragraph 6 shall vest as of the
<PAGE>

effective date of termination. If this Agreement is terminated by Maxygen for
any reason other than for cause or for any reason by Consultant prior to July 1,
2000, Maxygen agrees to pay the minimal Consulting Fees that would have been
payable through July 31, 2000.

          b.  For Cause. Either party may terminate this Agreement for cause,
effective immediately, upon written notice of termination for cause to the other
party. In the event of such termination by Maxygen, the stock options referred
to in Paragraph 6 shall be forfeited. For purposes of this Agreement, "cause"
includes but is not limited to:

              1)    Any material breach of this Agreement, including but not
limited to inducing or assisting infringement of any Maxygen patent or copyright
misappropriation of any Maxygen trade secret; and

              2)    Any act by one party that exposes the other to potential
liability to others for, among other things, personal injury, property damage,
patent infringement or trade secret misappropriation.

          c.  In the event of termination of this Agreement, Maxygen agrees to
pay for all services provided under this Agreement to the effective date of the
termination.

     9.   Indemnification.

          a.  Consultant will indemnify, defend, and hold harmless Maxygen, its
directors, officers, employees, agents and assigns against any and all liability
imposed or claimed, including attorneys' fees and other legal expenses, arising
directly or indirectly from any act or failure to act by Consultant in
connection with the performance of services under this Agreement.

          b.  Consultant will indemnify, defend and hold Maxygen harmless
against any and all liability imposed or claimed, including attorneys' fees and
other legal expenses, arising directly or indirectly from any violation of
federal, state or local law by Consultant in connection with the performance of
services under this Agreement, including but not limited to, the California Fair
Employment and Housing Act, Title VII of the Civil Rights Act of 1964, the Age
Discrimination in Employment Act, and the Americans with Disabilities Act.

          c.  Maxygen will have no duty to indemnify or defend Consultant.

     10.  Severability. Whenever possible, each provision of this Agreement will
be interpreted in such a manner as to be effective and valid under applicable
law. If any provision of this Agreement is held by a court of competent
jurisdiction to be invalid, void, or unenforceable, the remaining provisions
will nevertheless continue in full force without being impaired or invalidated
in any way.

     11.  Governing Law. This Agreement will be construed in accordance with the
law of the State of California without reference to principles of conflicts of
laws.
<PAGE>

     12.  Waiver. The waiver by either party of a breach of any provision of
this Agreement will not operate, or be construed, as a waiver of any subsequent
breach by the other party.

     13.  Assignment.  Consultant agrees that he will not assign this Agreement,
nor any duties or obligations under it, without the prior written consent of
Maxygen.  Maxygen shall have the right to assign this Agreement.

     14.  Notices.  All notices or other written communications provided for
under this Agreement will be in writing and will be deemed to have been given
either (i) upon personal delivery or confirmed facsimile transmission, (ii) one
day after deposit with a courier service for next day delivery, or (iii) five
days after deposit in the U.S. mail, registered mail--postage prepaid, to the
following addresses.

          a.  Joseph A. Affholter, Ph.D.
              17440 Lakeview Drive
              Morgan Hill, CA 95037

              Facsimile Number:  408/779-3580

          b.  Maxygen, Inc.
              515 Galveston Drive
              Redwood City, California 94063
              Attention: General Counsel

              Facsimile Number: 650/298-5803

     Either party may change its or his address by giving notice to the other
party in accordance with this paragraph.

     15.  Entire Agreement.  Except as provided in Paragraph 7.a above and the
separation letter, this Agreement supercedes any and all other agreements, both
oral or written, between Consultant and Maxygen with respect to the subject
matter of this Agreement, and the Agreement contains all of the promises and
agreements between the parties with regard to its subject matter.  Both
Consultant and Maxygen acknowledge that no representations, inducements,
promises, or agreements, oral or otherwise, have been made by the other party,
or anyone acting on behalf of the party, that are not contained in this
Agreement.  The parties also acknowledge that no agreement, statement or promise
that is not referenced or contained in this Agreement will be valid or binding.
Any modification of this Agreement will be effective only if it is in writing
and signed by Consultant and an authorized representative of Maxygen.

     16.  Arbitration of Disputes.  The parties agree that any controversy or
claim arising out of this Agreement, or any alleged breach of this Agreement,
will be subject to good faith mediation between the parties on mutually
acceptable terms.  Any remaining claim or controversy will be arbitrated in San
Francisco, California, before a single arbitrator, in accordance with the
Commercial Dispute Resolution Rules of the American Arbitration
<PAGE>

Association then in effect. The arbitrator's decision will be final and binding
on both parties. The prevailing party will be entitled to reasonable costs and
attorneys' fees, including expert witness fees.

     17.  Injunctive Relief.  Notwithstanding Paragraph 16, Consultant agrees
that a breach by him of his obligations under Paragraph 7 of this Agreement
relating to Confidential Information will cause Maxygen irreparable injury and
damage.  Consultant agrees that Maxygen is entitled to injunctive and other
equitable relief to prevent a breach of Paragraph 7 of the Agreement or to
secure its enforcement.  A request for equitable relief by Maxygen shall not be
a waiver of any other rights or remedies Maxygen or Consultant may have.

     18.  Attorneys' Fees.  If any legal action is brought that arises out of or
relates to this Agreement, including an action for injunctive relief, the
prevailing party will be entitled to reasonable attorneys' fees, which may be
set by the court in the same action or in a separate action brought for that
purpose, in addition to any other relief to which that party may be entitled.

     Executed on the dates set forth below.



Dated: January 28, 2000             /S/ Joseph A. Affholter, Ph.D.
      ------------------------      ----------------------------




Dated: January 28, 2000             MAXYGEN, INC.
      -------------------------


                                    By /s/ Russell Howard
                                    -----------------------------------------
                                           Russell Howard
                                           President and Chief Executive Officer
<PAGE>

                                   Exhibit A

                               Contract Services
                               -----------------


1.   Advice regarding the development of technologies relating to directed
evolution, gene shuffling and Molecular Breeding directed molecular evolution
technologies, and the use of such technologies to develop products and processes
using such technologies for commercial uses.

2.   Transitioning to new leadership within Maxygen all existing partner
management responsibilities, projects, initiatives, and potential business
partner communications in which consultant was involved or engaged while an
employee of Maxygen.

3.   Assisting in establishing new collaborative relationships between Maxygen
and third parties.

4.   Cooperation with Maxygen and its counsel in connection with any
intellectual property disputes with third parties in which Maxygen may become
engaged, which cooperation shall include not providing advice or guidance to any
third party with respect to any intellectual property dispute involving any type
of directed molecular evolution without Maxygen's prior written consent.

5.   Other services to be determined at the parties' mutual written consent.

<PAGE>

                                                                   EXHIBIT 10.18

                                PROMISSORY NOTE

$150,000                                                Redwood City, California
                                                                January 28, 2000

     Joseph Affholter and Roxanne Affholter ("Obligor"), for value received,
hereby promise to pay to the order of Maxygen, Inc. or holder ("Payee"), in
lawful money of the United States at the address of Payee set forth below, the
principal sum of One Hundred Fifty Thousand Dollars ($150,000), together with
interest on the unpaid principal from February 1, 2001 at the compounded annual
rate of 5.59%. Interest shall be due and payable on June 30 and December 31 of
each year. Unpaid principal together with all accrued interest shall be due and
payable with respect to Seventy-Two Thousand Five Hundred Dollars ($72,500) of
principal on April 1, 2003, and with respect to Seventy-Seven Thousand Five
Hundred Dollars ($77,500) of principal on March 30, 2004.

     If any payment of principal or interest on this note shall become due on a
Saturday, Sunday, or a public holiday under the laws of the State of California,
such payment shall be made on the next succeeding business day and such
extension of time shall be included in computing interest in connection with
such payment.

     This Note is secured by a Pledge Agreement of even date herewith.

     Upon payment in full of all principal and interest payable hereunder, this
Note shall be surrendered to Obligor for cancellation.

     Obligor waives presentment, demand for performance, notice of
nonperformance, protest, notice of protest, and notice of dishonor.  No delay on
the part of Payee in exercising any right hereunder shall operate as a waiver of
such right under this Note. This Note is being delivered in and shall be
construed in accordance with the laws of the State of California.

     In the event that Obligor fails to make payment on any date for payment
hereinabove specified of all principal and interest due hereunder on such date,
Obligor shall be deemed to be in default hereunder.  In the event of such
default, Payee may, at Payee's option and in Payee's sole discretion, five days
after giving notice of default to Obligor, accelerate the maturity of all
amounts due under this Note by giving notice of such acceleration.

     If the indebtedness represented by this Note or any part thereof is
collected at law or in equity or in bankruptcy, receivership or other judicial
proceedings or if this Note is placed in the hands of attorneys for collection
after default, Obligor agrees to pay, in addition to the principal and interest
payable hereon, reasonable attorneys' fees and costs incurred by Payee.
<PAGE>

     Any notice or other communication (except payment) required or permitted
hereunder shall be in writing and shall be deemed to have been given upon
delivery, if personally delivered or upon deposit if deposited in the United
States mail for mailing by certified mail, postage prepaid, and addressed as
follows:

     If to Payee:

                    Maxygen, Inc.
                    515 Galveston Drive
                    Redwood City, California 94063
                    Attention:  President

     If to Obligor:

                    Joseph A. Affholter
                    17440 Lakeview Drive
                    Morgan Hill, California 95037

     Any payment shall be deemed made upon receipt by Payee.  Payee or Obligor
may change their address for purposes of this paragraph by giving to the other
party notice in conformance with this paragraph of such new address.

                                       Obligors:

                                       /s/ Joseph A. Affholter
                                       -----------------------
                                           Joseph A. Affholter


                                       /s/ Roxanne B. Affholter
                                       ------------------------
                                           Roxanne B. Affholter
<PAGE>

                                 PAYMENTS MADE

<TABLE>
<CAPTION>
<S>                <C>                          <C>                    <C>
Date               Principal Amount             Interest               Received By
====               ================             ========               ===========



</TABLE>

<PAGE>

                                                                   EXHIBIT 10.19

                               PLEDGE AGREEMENT

     This PLEDGE AGREEMENT ("Agreement"), dated effective as of January 28,
2000, is made between Joseph Affholter and Roxanne Affholter ("Pledgors"), and
Maxygen, Inc. ("Pledgee" and "Pledge Holder").

     For good and valuable consideration and to secure the payment of Pledgors'
indebtedness to the Pledgee, the parties agree as follows:

1.   Pledgors' Indebtedness.

     (a)  Pledgors have borrowed One Hundred Fifty Thousand Dollars ($150,000)
from the Pledgee, evidenced by a Promissory Note.

     (b)  Pledgors have executed the Note and are required to secure the Note by
delivery of this Agreement.

2.   Pledge.

     Pledgors hereby pledge to the Pledge Holder on behalf of the Pledgee, and
grant to the Pledgee a security interest in, the following (the "Pledged
Collateral"): (i) that number of shares of the Common Stock of Maxygen, Inc.
having a market value of Three Hundred Thousand Dollars ($300,000) calculated
based on the closing price of Maxygen common stock on January 27, 2000 (the
"Shares") and the certificates representing such Shares, and all other
securities, instruments, dividends, cash, and other property that may be
received, receivable, or otherwise distributed in respect of or in exchange for
any of the Shares; and (ii) all other proceeds of the foregoing. If, at any
time, the Pledgee reasonably believes that the Pledged Collateral is
insufficient to guarantee payment of unpaid principal and interest of the Note,
Pledgee in its discretion may demand the pledge of additional collateral by
Pledgors and failure by the Pledgors to deliver such additional collateral
within fifteen (15) days from such demand shall be an Event of Default.

3.   Security for Obligations.

     (a)  This Agreement secures the payment of all of the Pledgors' present and
future obligations, duties, and liabilities under the Note and under this
Agreement (all referred to as the "Obligations").

     (b)  This Agreement shall create a continuing security interest in the
Pledged Collateral and shall (i) remain in full force and effect until payment
in full of the Obligations; (ii) be binding upon Pledgors and their successors
and assigns; and (iii) inure to the benefit of the Pledgee and its successors,
transferees, and assigns.
<PAGE>

4.   Delivery of Pledged Shares.

     All certificates or instruments representing or evidencing the Shares and
other Pledged Collateral shall be held by the Pledge Holder on behalf of the
Pledgee under this Agreement and shall be in suitable form for transfer by
delivery, or shall be accompanied by duly executed instruments of transfer or
assignment in blank, all in form and substance satisfactory to the Pledgee or
the Pledge Holder.  If Pledgors fail to perform any Obligation, the Pledge
Holder or the Pledgee may perform, or cause performance of, that Obligation, and
the expenses incurred in connection with that performance shall be payable by
Pledgors under Section 8.

5.   Rights in Absence of Default.

     (a)  So long as there has been and is no Event of Default (as defined in
Section 7(a) below) or event which, with the giving of notice or the lapse of
time, or both, would become an Event of Default:

          (i)   Pledgors shall be entitled to exercise any and all voting and
other consensual rights pertaining to any or all of the Pledged Collateral for
any purpose not inconsistent with the terms of this Agreement or the Note;
provided that Pledgors shall not exercise or shall refrain from exercising any
of those rights if, in the judgment of the Pledgee, that action would have a
material adverse effect on the value of the Pledged Collateral or any part of
it.

          (ii)  Dividends, other distributions, and interest paid or payable in
respect of, and instruments and other property received, receivable, or
otherwise distributed in respect of, or in exchange for, any Pledged Collateral
shall constitute, and shall be immediately delivered to the Pledge Holder to
hold as, Pledged Collateral, and shall, if received by Pledgors, be received in
trust for the benefit of the Pledgee, be segregated from other property or funds
of Pledgors, and be immediately delivered to the Pledge Holder as Pledged
Collateral in the same form as so received (with any necessary endorsement).

          (iii) The Pledge Holder shall execute and deliver (or cause to be
executed and delivered) to Pledgors all such proxies and other instruments as
Pledgors may reasonably request for the purpose of enabling them to exercise the
voting and other rights that they are entitled to exercise pursuant to paragraph
(i) of this Section 5(a).

     (b)  When and so long as there is an Event of Default or an event which,
with the giving of notice or the lapse of time, or both, would become an Event
of Default, all rights of Pledgors to exercise the voting and other rights that
they would otherwise be entitled to exercise pursuant to Section 5(a)(i) shall
cease, and all those rights shall

                                       2
<PAGE>

become vested in the Pledge Holder, who shall then have the sole right to
exercise those voting and other rights.

6.   Transfers and Liens.

     Pledgors agree that they will not (i) sell or otherwise dispose of, or
grant any option with respect to, any of the Pledged Collateral without the
prior written consent of the Pledgee; or (ii) create or permit to exist any lien
upon or with respect to any of the Pledged Collateral, except for the security
interest under this Agreement.

7.   Events of Default; Remedies upon Default.

     (a)  The following each shall constitute events of default ("Events of
Default") under this Agreement:

          (i)   If Pledgors fail to perform or observe any term, covenant, or
Obligation under this Agreement or the Note, or if any representation or
warranty made by Pledgors in this Agreement or the Note is untrue or misleading
in any material respect as of the date with respect to which that representation
or warranty was made;

          (ii)  If a notice of lien, levy, or assessment is filed or recorded
with respect to all or a substantial part of the Pledged Collateral, except for
a lien that relates to current taxes not yet due and payable, and if the
applicable claim is not discharged or satisfied within thirty days of Pledgors'
actual or constructive knowledge of that filing or recordation; and

          (iii) If all or a substantial part of the Pledged Collateral is
attached, seized, or subjected to a writ or distress warrant, or is levied upon,
or comes within the possession of any receiver, trustee, custodian, or assignee
for the benefit of creditors, and that Pledged Collateral is not returned to
Pledgors or the writ, distress warrant, or levy is not dismissed, stayed, or
lifted within thirty days.

     (b)  When and so long as there is any Event of Default, the Pledgee may
exercise in respect of the Pledged Collateral, in addition to other rights and
remedies provided for in this Agreement or otherwise available to it, all the
rights and remedies of a secured party upon a default under the Uniform
Commercial Code in effect in the State of California at that time.

8.   Expenses.

     On demand, Pledgors will pay the Pledge Holder all reasonable expenses,
including attorneys' fees and costs, which the Pledge Holder may incur in
connection with (i) the exercise or enforcement of any of the rights of the
Pledge Holder or the

                                       3
<PAGE>

Pledgee under this Agreement; or (ii) Pledgors' failure to perform or observe
any of the provisions of this Agreement.

9.   Security Interest Absolute.

     All rights and security interests of the Pledge Holder or Pledgee, and all
Obligations of  Pledgors, under this Agreement shall be absolute and
unconditional irrespective of: (i) any lack of validity or enforceability of the
Note or any other agreement or instrument relating to it; (ii) any change in the
time, manner, or place of payment of, or in any other term of, any of the
Obligations, or any other amendment or wavier of or consent to any departure
from the Note; (iii) any exchange, release, or non-perfection of any other
collateral, or any release, amendment, or waiver of any of the Obligations; or
(iv) any other circumstance that might otherwise constitute a defense available
to, or a discharge or, Pledgors in respect of the Obligations or of this
Agreement.

10.  Further Assurances.

     Pledgors agree that at any time and from time to time, Pledgors will
promptly execute and deliver all further instruments and documents, and take all
further action, that may be necessary or desirable, or that the Pledge Holder
may reasonably request, in order to perfect and protect any security interest
granted or purported to be granted by this Agreement or to enable the Pledge
Holder to exercise and enforce the rights and remedies under this Agreement with
respect to any Pledged Collateral.

11.  Entire Agreement; Amendment; Wavier.

     This Agreement and the Note embody the entire agreement of the parties
hereto with respect to the subject matter of this Agreement and supersede all
prior agreements with respect to that subject matter.  This Agreement may not be
amended or modified except in a writing signed by both parties.  No waiver of
any  provision in this Agreement shall be deemed to, or shall operate as a
waiver of any other provision, whether or not similar, nor shall any waiver
constitute a continuing waiver.  Except as expressly provided in this Agreement,
no waiver shall be binding unless executed in writing by the party making the
waiver.

12.  Notices.

     Any notice, request, claim or other communication required or permitted
hereunder will be in writing and will be deemed to have been duly given if
delivered by hand or if sent by certified mail, postage and certification
prepaid, to Pledgors at 17440 Lakeview Drive, Morgan Hill, California 95037, or
to the Pledgee and the Pledge Holder at 515 Galveston Drive, Redwood City,
California 94063, or to such other address

                                       4
<PAGE>

or addresses as any party may have furnished to the other in writing in
accordance herewith.

13.  Captions.

     Captions are used for reference purposes only and should be ignored in the
interpretation of the Agreement.  Unless the context requires otherwise, all
references in this Agreement to Sections are to the sections of this Agreement.

14.  Governing Law; Terms.

     This Agreement shall be governed by and construed in accordance with the
laws of the State of California applicable to contracts wholly made and
performed in the State of California.  Unless otherwise defined above, terms
defined in Division 9 of the Uniform Commercial Code as adopted in the State of
California are used in this Agreement with their statutory meanings.

15.  Counterparts.

     This Agreement may be executed in one or more counterparts all of which
together shall constitute one and the same instrument.

     The parties have duly executed this Agreement as of the date first written
above.



 /s/ Joseph A. Affholter
- -----------------------------------
     Joseph A. Affholter
     "Pledgor"


 /s/ Roxanne B. Affholter
- -----------------------------------
     Roxanne B. Affholter
     "Pledgor"

MAXYGEN, INC.


By: /s/ Russell Howard
   --------------------------------
   "Pledge Holder" and "Pledgee"

                                       5

<PAGE>

                                                                   EXHIBIT 10.20

                             PUBLIC HEALTH SERVICE

                COOPERATIVE RESEARCH AND DEVELOPMENT AGREEMENT


This Cooperative Research and Development Agreement, hereinafter referred to as
the "CRADA," consists of this Cover Page, an attached Agreement, and various
Appendices referenced in the Agreement.  This Cover Page serves to identify the
Parties to this CRADA:

          (1)  the following Bureau(s), Institute(s), Center(s) or Division(s)
of the National Institutes of Health ("NIH"), the Food and Drug Administration
("FDA"), and the Centers for Disease Control and Prevention ("CDC"):

The National Cancer Institute hereinafter singly or collectively referred to as
the Public Health Service ("PHS"); and

          (2)  Maxygen, Incorporated, which has offices at 515 Galveston Drive,
Redwood City, California, 94063 hereinafter referred to as the "Collaborator."



THE SYMBOL "*******" IS USED TO INDICATE THAT A PORTION OF THE EXHIBIT HAS BEEN
OMITTED AND FILED SEPARATELY WITH THE COMMISSION.  CONFIDENTIAL TREATMENT HAS
BEEN REQUESTED WITH RESPECT TO THE OMITTED PORTIONS.
<PAGE>

                COOPERATIVE RESEARCH AND DEVELOPMENT AGREEMENT

Article 1.  Introduction

This Cooperative Research and Development Agreement (CRADA) between PHS and the
Collaborator will be effective when signed by all Parties.  The research and
development activities which will be undertaken by each of the Parties in the
course of this CRADA are detailed in the Research Plan (RP) which is attached as
Appendix A.  The funding and staffing commitments of the Parties are set forth
in Appendix B.  Any exceptions or changes to the CRADA are set forth in Appendix
C.  This CRADA is made under the authority of the Federal Technology Transfer
Act, 15 U.S.C. (S)3710a and is governed by its terms.

Article 2.  Definitions

As used in this CRADA, the following terms shall have the indicated meanings:

2.1  "Affiliate" means any corporation or other business entity controlled by,
     controlling, or under common control with Collaborator. For this purpose, A
     "control" means direct or indirect beneficial ownership of at least fifty
     (50) percent of the voting stock or at least fifty (50) percent interest in
     the income of such corporation or other business.

2.2  "Cooperative Research and Development Agreement" or "CRADA" means this
     Agreement, entered into by PHS pursuant to the Federal Technology Transfer
     Act of 1986, as amended, 15 U.S.C. 3710a et seq. and Executive Order 12591
                                              ------
     of October 10, 1987.

2.3  "Government" means the Government of the United States as represented
     through the PHS agency that is a Party to this agreement.

2.4  "IP" means intellectual property.

2.5  "Invention" means any invention or discovery which is or may be patentable
     or otherwise protected under title 35, United States Code, or any novel
     variety or plant which is or may be protectable under the Plant Variety
     Protection Act (7 U.S.C. 2321 et seq.).
                                   ------

2.6  "Principal Investigator(s)" or "PIs" means the persons designated
     respectively by the Parties to this CRADA who will be responsible for the
     scientific and technical conduct of the RP.

2.7  "Proprietary/Confidential Information" means confidential scientific,
     business, or financial information provided that such information does not
     include:

     2.7.1.  information that is publicly known or available from other sources
             who are not under a confidentiality obligation to the source of the
             information;

                                       2
<PAGE>

     2.7.2.  information which has been made available by its owners to others
             without a confidentiality obligation;

     2.7.3.  information which is already known by or available to the receiving
             Party without a confidentiality obligation; or

     2.7.4.  information which relates to potential hazards or cautionary
             warnings associated with the production, handling or use of the
             subject matter of the Research Plan of this CRADA.

2.8  "Research Materials" means all tangible materials other than Subject Data
     first produced in the performance of this CRADA.

2.9  "Research Plan" or "RP" means the statement in Appendix A of the respective
     research and development commitments of the Parties to this CRADA.

2.10 "Subject Invention" means any Invention of the Parties, conceived or first
     actually reduced to practice in the performance of the Research Plan of
     this CRADA.

2.11 "Subject Data" means all recorded information first produced in the
     performance of this CRADA by the Parties.

Article 3.  Cooperative Research

3.1  Principal Investigators.  PHS research work under this CRADA will be
     performed by the PHS laboratory identified in the RP, and the PHS Principal
     Investigator (PI) designated in the RP will be responsible for the
     scientific and technical conduct of this project on behalf of PHS.  Also
     designated in the RP is the Collaborator PI who will be responsible for the
     scientific and technical conduct of this project on behalf of the
     Collaborator.

3.2  Research Plan Change.  The RP may be modified by mutual written consent of
     the Principal Investigators.  Substantial changes in the scope of the RP
     will be treated as amendments under Article 13.6.

Article 4.  Reports

4.1  Interim Reports.  The Parties shall exchange formal written interim
     progress reports on a schedule agreed to by the PIs, but at least within
     twelve (12) months after this CRADA becomes effective and at least within
     every twelve (12) months thereafter.  Such reports shall set forth the
     technical progress made, identifying such problems as may have been
     encountered and establishing goals and objectives requiring further effort,
     any modifications to the Research Plan pursuant to Article 3.2, and all
     CRADA-related patent applications filed.

4.2  Final Reports.  The Parties shall exchange final reports of their results
     within four (4) months after completing the projects described in the RP or
     after the expiration or termination of this CRADA.

                                       3
<PAGE>

Article 5.  Financial and Staffing Obligations

5.1  PHS and Collaborator Contributions.  The contributions of the Parties,
     including payment schedules, if applicable, are set forth in Appendix B.
     PHS shall not be obligated to perform any of the research specified herein
     or to take any other action required by this CRADA if the funding is not
     provided as set forth in Appendix B.  PHS shall return excess funds to the
     Collaborator when it sends its final fiscal report pursuant to Article 5.2,
     except for staffing support pursuant to Article 10.3.  Collaborator
     acknowledges that the U.S. Government will have the authority to retain and
     expend any excess funds for up to one (1) year subsequent to the expiration
     or termination of the CRADA to cover any costs incurred during the term of
     the CRADA in undertaking the work set forth in the RP.

5.2  Accounting Records.  PHS shall maintain separate and distinct current
     accounts, records, and other evidence supporting all its obligations under
     this CRADA, and shall provide the Collaborator a final fiscal report
     pursuant to Article 4.2.

5.3  Capital Equipment.  Equipment purchased by PHS with funds provided by the
     Collaborator shall be the property of PHS.  All capital equipment provided
     under this CRADA by one party for the use of another Party remains the
     property of the providing Party unless other disposition is mutually agreed
     upon by in writing by the Parties.  If title to this equipment remains with
     the providing Party, that Party is responsible for maintenance of the
     equipment and the costs of its transportation to and from the site where it
     will be used.

Article 6.  Intellectual Property Rights and Patent Applications

6.1  Reporting.  The Parties shall promptly report to each other in writing each
     Subject Invention resulting from the research conducted under this CRADA
     that is reported to them by their respective employees.  Each Party shall
     report all Subject Inventions to the other Party in sufficient detail to
     determine inventorship.  Such reports shall be treated as
     Proprietary/Confidential Information in accordance with Article 8.4.

6.2  Collaborator Employee Inventions.  If the Collaborator does not elect to
     retain its IP rights, the Collaborator shall offer to assign these IP
     rights to the Subject Invention to PHS pursuant to Article 6.5.  If PHS
     declines such assignment, the Collaborator may release its IP rights as it
     may determine.

6.3  PHS Employee Inventions.  PHS on behalf of the U.S. Government may elect to
     retain IP rights to each Subject Invention made solely by PHS employees.
     If PHS does not elect to retain IP rights, PHS shall offer to assign these
     IP rights to such Subject Invention to the Collaborator pursuant to Article
     6.5.  If the Collaborator declines such assignment, PHS may release IP
     rights in such Subject Invention to its employee inventors pursuant to
     Article 6.6.

6.4  Joint Inventions.  Each Subject Invention made jointly by PHS and
     Collaborator employees shall be jointly owned by PHS and the Collaborator.
     The Collaborator may elect to file the joint patent or other IP
     application(s) thereon and shall notify PHS promptly upon making this
     election.  If the Collaborator decides to file such applications,

                                       4
<PAGE>

     it shall do so in a timely manner and at its own expense. If the
     Collaborator does not elect to file such application(s), PHS on behalf of
     the U.S. Government shall have the right to file the joint application(s)
     in a timely manner and at its own expense. If either Party decides not to
     retain its IP rights to a jointly owned Subject Invention, it shall offer
     to assign such rights to the other Party pursuant to Article 6.5. If the
     other Party declines such assignment, the offering Party may release its IP
     rights as provided in Articles 6.2, 6.3, and 6.6.

6.5  Filing of Patent Applications.  With respect to Subject Inventions made by
     the Collaborator as described in Article 6.2, or by PHS as described in
     Article 6.3, a Party exercising its right to elect to retain IP rights to a
     Subject Invention agrees to file patent or other IP applications in a
     timely manner and at its own expense and after consultation with the other
     Party.  The Party shall notify the other Party of its decision regarding
     filing in countries other than the United States in a timely manner.  The
     Party may elect not to file a patent or other IP application thereon in any
     particular country or countries provided it so advises the other Party
     ninety (90) days prior to the expiration of any applicable filing deadline,
     priority period or statutory bar date, and hereby agrees to assign its IP
     right, title and interest in such country or countries to the Subject
     Invention to the other Party and to cooperate in the preparation and filing
     of a patent or other IP applications.  In any countries in which title to
     patent or other IP rights is transferred to the Collaborator, the
     Collaborator agrees that PHS inventors will share in any royalty
     distribution that the Collaborator pays to its own inventors.

6.6  Release to Inventors.  In the event neither of the Parties to this CRADA
     elects to file a patent or other IP application on a Subject Invention,
     either or both (if a joint invention) may retain or release their IP rights
     in accordance with their respective policies and procedures.  However, the
     Government shall retain a nonexclusive, non-transferable, irrevocable,
     royalty-free license to practice any such Subject Invention or have it
     practiced throughout the world by or on behalf of the Government.

6.7  Patent Expenses.  The expenses attendant to the filing of patent or other
     IP applications generally shall be paid by the Party filing such
     application.  If an exclusive license to any Subject Invention is granted
     to the Collaborator, the Collaborator shall be responsible for all past and
     future out-of-pocket expenses in connection with the preparation, filing,
     prosecution and maintenance of any applications claiming such exclusively-
     licensed inventions and any patents or other IP grants that may issue on
     such applications.  The Collaborator may waive its exclusive license rights
     on any application, patent or other IP grant at any time, and incur no
     subsequent compensation obligation for that application, patent or IP
     grant.

6.8  Prosecution of Intellectual Property Applications.  Within one month of
     receipt or filing,  each Party shall provide the other Party with copies of
     the applications and all documents received from or filed with the relevant
     patent or other IP office in connection with the prosecution of such
     applications.  Each Party shall also provide the other Party with the power
     to inspect and make copies of all documents retained in the patent or other
     IP application files by the applicable patent or other IP office.  Where
     licensing is contemplated by Collaborator, the Parties agree to consult
     with each other with respect to

                                       5
<PAGE>

     the prosecution of applications for PHS Subject Inventions described in
     Article 6.3 and joint Subject Inventions described in Article 6.4. If the
     Collaborator elects to file and prosecute IP applications on joint Subject
     Inventions pursuant to Article 6.4, PHS will be granted an associate power
     of attorney (or its equivalent) on such IP applications.

Article 7.  Licensing

7.1  Option for Commercialization License.  With respect to Government IP rights
     to any Subject Invention not made solely by the Collaborator's employees
     for which a patent or other IP application is filed, PHS hereby grants to
     the Collaborator an exclusive option to elect an exclusive or nonexclusive
     commercialization license, which is substantially in the form of the
     appropriate model PHS license agreement.  This option does not apply to
     Subject Inventions conceived prior to the effective date of this CRADA that
     are reduced to practice under this CRADA, if prior to that reduction to
     practice, PHS has filed a patent application on the invention and has
     licensed it or offered to license it to a third party.  The terms of the
     license will fairly reflect the nature of the invention, the relative
     contributions of the Parties to the invention and the CRADA, the risks
     incurred by the Collaborator and the costs of subsequent research and
     development needed to bring the invention to the marketplace.  The field of
     use of the license will be commensurate with the scope of the RP.

7.2  Exercise of License Option.  The option of Article 7.1 must be exercised by
     written notice mailed within three (3) months after either (i) Collaborator
     receives written notice from PHS that the patent or other IP application
     has been filed; or (ii) the date Collaborator files such IP application.
     Exercise of this option by the Collaborator initiates a negotiation period
     that expires nine (9) months after the exercise of the option.  If the last
     proposal by the Collaborator has not been responded to in writing by PHS
     within this nine (9) month period, the negotiation period shall be extended
     to expire one (1) month after PHS so responds, during which month the
     Collaborator may accept in writing the final license proposal of PHS.  In
     the absence of such acceptance, or an extension of the time limits by PHS,
     PHS will be free to license such IP rights to others.  In the event that
     the Collaborator elects the option for an exclusive license, but no such
     license is executed during the negotiation period, PHS agrees not to make
     an offer for an exclusive license on more favorable terms to a third party
     for a period of six (6) months without first offering Collaborator those
     more favorable terms. These times may be extended at the sole discretion of
     PHS upon good cause shown in writing by the Collaborator.

7.3  License for PHS Employee Inventions and Joint Inventions.  Pursuant to 15
     U.S.C. (S) 3710a(b)(1)(A), for Subject Inventions made under this CRADA by
     a PHS employee(s) or jointly by such employee(s) and employees of the
     Collaborator pursuant to Articles 6.3 and 6.4 and licensed pursuant to the
     option of Article 7.1, the Collaborator grants to the Government a
     nonexclusive, nontransferable, irrevocable, paid-up license to practice the
     invention or have the invention practiced throughout the world by or on
     behalf of the Government.  In the exercise of such license, the Government
     shall not publicly disclose trade secrets or commercial or financial
     information that is privileged or confidential

                                       6
<PAGE>

     within the meaning of 5 U.S.C. 552(b)(4) or which would be considered as
     such if it had been obtained from a non-Federal party.

7.4  License in Collaborator Inventions.  Pursuant to 15 U.S.C. (S) 3710a(b)(2),
     for inventions made solely by Collaborator employees under this CRADA
     pursuant to Article 6.2, the Collaborator grants to the Government a
     nonexclusive, nontransferable, irrevocable, paid-up license to practice the
     invention or have the invention practiced throughout the world by or on
     behalf of the Government for research or other Government purposes.

7.5  Third Party License.  Pursuant to 15 U.S.C. (S) 3710a(b)(1)(B), if PHS
     grants an exclusive license to a Subject Invention made wholly by PHS
     employees or jointly with a Collaborator under this CRADA, pursuant to
     Articles 6.3 and 6.4, the Government shall retain the right to require the
     Collaborator to grant to a responsible applicant a nonexclusive, partially
     exclusive, or exclusive sublicense to use the invention in Collaborator's
     licensed field of use on terms that are reasonable under the circumstances;
     or if the Collaborator fails to grant such a license, to grant the license
     itself.  The exercise of such rights by the Government shall only be in
     exceptional circumstances and only if the Government determines (i) the
     action is necessary to meet health or safety needs that are not reasonably
     satisfied by Collaborator, (ii) the action is necessary to meet
     requirements for public use specified by Federal regulations, and such
     requirements are not reasonably satisfied by the Collaborator; or (iii) the
     Collaborator has failed to comply with an agreement containing provisions
     described in 15 U.S.C. 3710a(c)(4)(B).  The determination made by the
     Government under this Article is subject to administrative appeal and
     judicial review under 35 U.S.C. 203(2).

7.6  Joint Inventions Not Exclusively Licensed.  In the event that the
     Collaborator does not acquire an exclusive commercialization license to IP
     rights in all fields in joint Subject Inventions described in Article 6.4,
     then each Party shall have the right to use the joint Subject Invention and
     to license its use to others in all fields not exclusively licensed to
     Collaborator.  The Parties may agree to a joint licensing approach for such
     IP rights.

Article 8.  Proprietary Rights and Publication

8.1  Right of Access.  PHS and the Collaborator agree to exchange all Subject
     Data produced in the course of research under this CRADA.  Research
     Materials will be shared equally by the Parties to the CRADA unless other
     disposition is agreed to by the Parties.  All Parties to this CRADA will be
     free to utilize Subject Data and Research Materials for their own purposes,
     consistent with their obligations under this CRADA.

8.2  Ownership of Subject Data and Research Materials.  Subject to the sharing
     requirements of Paragraph 8.1 and the regulatory filing requirements of
     Paragraph 8.3, the producing Party will retain ownership of and title to
     all Subject Inventions, all Subject Data and all Research Materials
     produced solely by their investigators.  Jointly developed Subject
     Inventions, Subject Data and Research Materials will be jointly owned.

                                       7
<PAGE>

8.3  Dissemination of Subject Data and Research Materials.  To the extent
     permitted by law, the Collaborator and PHS agree to use reasonable efforts
     to keep Subject Data and Research Materials confidential until published or
     until corresponding patent applications are filed.  Any information that
     would identify human subjects of research or patients will always be
     maintained confidentially.  To the extent permitted by law, the
     Collaborator shall have the exclusive right to use any and all CRADA
     Subject Data in and for any regulatory filing by or on behalf of
     Collaborator, except that PHS shall have the exclusive right to use Subject
     Data for that purpose, and authorize others to do so, if the CRADA is
     terminated or if Collaborator abandons its commercialization efforts.

8.4  Proprietary/Confidential Information.  Each Party agrees to limit its
     disclosure of Proprietary/Confidential Information to the amount necessary
     to carry out the Research Plan of this CRADA, and shall place a
     confidentiality notice on all such information.  Confidential oral
     communications shall be reduced to writing within 30 days by the disclosing
     Party.  Each Party receiving Proprietary/Confidential Information agrees
     that any information so designated shall be used by it only for the
     purposes described in the attached Research Plan.  Any Party may object to
     the designation of information as Proprietary/Confidential Information by
     another Party.  Subject Data and Research Materials developed solely by the
     Collaborator may be designated as Proprietary/Confidential Information when
     they are wholly separable from the Subject Data and Research Materials
     developed jointly with PHS investigators, and advance designation of such
     data and material categories is set forth in the RP.  The exchange of other
     confidential information, e.g.,  patient-identifying data, should be
     similarly limited and treated.  Jointly developed Subject Data and Research
     Material derived from the Research Plan may be disclosed by Collaborator to
     a third party under a confidentiality agreement for the purpose of possible
     sublicensing pursuant to the Licensing Agreement and subject to Article
     8.7.

8.5  Protection of Proprietary/Confidential Information.
     Proprietary/Confidential Information shall not be disclosed, copied,
     reproduced or otherwise made available to any other person or entity
     without the consent of the owning Party except as required under court
     order or the Freedom of Information Act (5 U.S.C. ' 552). Each Party agrees
     to use its best efforts to maintain the confidentiality of
     Proprietary/Confidential Information. Each Party agrees that the other
     Party is not liable for the disclosure of Proprietary/Confidential
     Information which, after notice to and consultation with the concerned
     Party, the other Party in possession of the Proprietary/Confidential
     Information determines may not be lawfully withheld, provided the concerned
     Party has been given an opportunity to seek a court order to enjoin
     disclosure.

8.6  Duration of Confidentiality Obligation.  The obligation to maintain the
     confidentiality of Proprietary/Confidential Information shall expire at the
     earlier of the date when the information is no longer Proprietary
     Information as defined in Article 2.7 or three (3) years after the
     expiration or termination date of this CRADA.  The Collaborator may request
     an extension to this term when necessary to protect
     Proprietary/Confidential Information relating to products not yet
     commercialized.

                                       8
<PAGE>

8.7  Publication.  The Parties are encouraged to make publicly available the
     results of their research.  Before either Party submits a paper or abstract
     for publication or otherwise intends to publicly disclose information about
     a Subject Invention, Subject Data or Research Materials, the other Party
     shall be provided thirty (30) days to review the proposed publication or
     disclosure to assure that Proprietary/Confidential Information is
     protected.  The publication or other disclosure shall be delayed for up to
     thirty (30) additional days upon written request by any Party as necessary
     to preserve U.S. or foreign patent or other IP rights.

Article 9.  Representations and Warranties

9.1  Representations and Warranties of PHS.  PHS hereby represents and warrants
     to the Collaborator that the official signing this CRADA has authority to
     do so.

9.2  Representations and Warranties of the Collaborator.

     9.2.1.  The Collaborator hereby represents and warrants to PHS that the
             Collaborator has the requisite power and authority to enter into
             this CRADA and to perform according to its terms, and that the
             Collaborator's official signing this CRADA has authority to do so.
             The Collaborator further represents that it is financially able to
             satisfy any funding commitments made in Appendix B.

     9.2.2.  The Collaborator certifies that the statements herein are true,
             complete, and accurate to the best of its knowledge. The
             Collaborator is aware that any false, fictitious, or fraudulent
             statements or claims may subject it to criminal, civil, or
             administrative penalties.

Article 10.  Termination

10.1 Termination By Mutual Consent.  PHS and the Collaborator may terminate this
     CRADA, or portions thereof, at any time by mutual written consent.  In such
     event the Parties shall specify the disposition of all property,
     inventions, patent or other IP applications and other results of work
     accomplished or in progress, arising from or performed under this CRADA,
     all in accordance with the rights granted to the Parties under the terms of
     this Agreement.

10.2 Unilateral Termination.  Either PHS or the Collaborator may unilaterally
     terminate this entire CRADA at any time by giving written notice at least
     thirty (30) days prior to the desired termination date, and any rights
     accrued in property, patents or other IP rights shall be disposed of as
     provided in paragraph 10.1.

10.3 Staffing.  If this CRADA is mutually or unilaterally terminated prior to
     its expiration, funds will nevertheless remain available to PHS for
     continuing any staffing commitment made by the Collaborator pursuant to
     Article 5.1 above and Appendix B, if applicable, for a period of six (6)
     months after such termination.  If there are insufficient funds to cover
     this expense, the Collaborator agrees to pay the difference.

                                       9
<PAGE>

10.4 New Commitments.  No Party shall make new commitments related to this CRADA
     after a mutual termination or notice of a unilateral termination and shall,
     to the extent feasible, cancel all outstanding commitments and contracts by
     the termination date.

10.5 Termination Costs.  Concurrently with the exchange of final reports
     pursuant to Articles 4.2 and 5.2, PHS shall submit to the Collaborator for
     payment a statement of all costs incurred prior to the date of termination
     and for all reasonable termination costs including the cost of returning
     Collaborator property or removal of abandoned property, for which
     Collaborator shall be responsible.

Article 11.  Disputes

11.1 Settlement.  Any dispute arising under this CRADA which is not disposed of
     by agreement of the Principal Investigators shall be submitted jointly to
     the signatories of this CRADA.  If the signatories are unable to jointly
     resolve the dispute within thirty (30) days after notification thereof, the
     Assistant Secretary for Health (or his/her designee or successor) shall
     propose a resolution.  Nothing in this Article shall prevent any Party from
     pursuing any additional administrative remedies that may be available and,
     after exhaustion of such administrative remedies, pursuing all available
     judicial remedies.

11.2 Continuation of Work.  Pending the resolution of any dispute or claim
     pursuant to this Article, the Parties agree that performance of all
     obligations shall be pursued diligently in accordance with the direction of
     the PHS signatory.

Article 12.  Liability

12.1 Property.  The U.S. Government shall not be responsible for damages to any
     Collaborator property  provided to PHS, where Collaborator retains title to
     the property, or any property acquired by Collaborator for its own use
     pursuant to this CRADA.

12.2 NO WARRANTIES.  EXCEPT AS SPECIFICALLY STATED IN ARTICLE 9, THE PARTIES
     MAKE NO EXPRESS OR IMPLIED WARRANTY AS TO ANY MATTER WHATSOEVER, INCLUDING
     THE CONDITIONS OF THE RESEARCH OR ANY INVENTION OR PRODUCT, WHETHER
     TANGIBLE OR INTANGIBLE, MADE, OR DEVELOPED UNDER THIS CRADA, OR THE
     OWNERSHIP, MERCHANTABILITY, OR FITNESS FOR A PARTICULAR PURPOSE OF THE
     RESEARCH OR ANY INVENTION OR PRODUCT.

12.3 Indemnification.  The Collaborator agrees to hold the U.S. Government
     harmless and to indemnify the Government for all liabilities, demands,
     damages, expenses and losses arising out of the use by the Collaborator for
     any purpose of the Subject Data, Research Materials and/or Subject
     Inventions produced in whole or part by PHS employees under this CRADA,
     unless due to the negligence or willful misconduct of PHS, its employees,
     or agents.  The Collaborator shall be liable for any claims or damages it
     incurs in connection with this CRADA.  PHS has no authority to indemnify
     the Collaborator.

12.4 Force Majeure.  Neither Party shall be liable for any unforeseeable event
     beyond its reasonable control not caused by the fault or negligence of such
     Party, which causes such

                                       10
<PAGE>

     Party to be unable to perform its obligations under this CRADA, and which
     it has been unable to overcome by the exercise of due diligence. In the
     event of the occurrence of such a force majeure event, the Party unable to
     perform shall promptly notify the other Party. It shall further use its
     best efforts to resume performance as quickly as possible and shall suspend
     performance only for such period of time as is necessary as a result of the
     force majeure event.

Article 13.  Miscellaneous

13.1 Governing Law.  The construction, validity,  performance and effect of this
     CRADA shall be governed by Federal law, as applied by the Federal Courts in
     the District of Columbia.  Federal law and regulations will preempt any
     conflicting or inconsistent provisions in this CRADA.

13.2 Entire Agreement.  This CRADA constitutes the entire agreement between the
     Parties concerning the subject matter of this CRADA and supersedes any
     prior understanding or written or oral agreement.

13.3 Headings.  Titles and headings of the articles and subarticles of this
     CRADA are for convenient reference only, do not form a part of this CRADA,
     and shall in no way affect its interpretation.  The PHS component that is
     the Party for all purposes of this CRADA is the Bureau(s), Institute(s),
     Center(s) or Division(s) listed on the Cover Page herein.

13.4 Waivers.  None of the provisions of this CRADA shall be considered waived
     by any Party unless such waiver is given in writing to the other Party.
     The failure of a Party to insist upon strict performance of any of the
     terms and conditions hereof, or failure or delay to exercise any rights
     provided herein or by law, shall not be deemed a waiver of any rights of
     any Party.

13.5 Severability.  The illegality or invalidity of any provisions of this CRADA
     shall not impair, affect, or invalidate the other provisions of this CRADA.

13.6 Amendments.  If either Party desires a modification to this CRADA, the
     Parties shall, upon reasonable notice of the proposed modification or
     extension by the Party desiring the change, confer in good faith to
     determine the desirability of such modification or extension.  Such
     modification shall not be effective until a written amendment is signed by
     the signatories to this CRADA or by their representatives duly authorized
     to execute such amendment.

13.7 Assignment.  Neither this CRADA nor any rights or obligations of any Party
     hereunder shall be assigned or otherwise transferred by either Party
     without the prior written consent of the other Party.

13.8 Notices.  All notices pertaining to or required by this CRADA shall be in
     writing and shall be signed by an authorized representative and shall be
     delivered by hand or sent by certified mail, return receipt requested, with
     postage prepaid, to the addresses indicated on the signature page for each
     Party.  Notices regarding the exercise of license options

                                       11
<PAGE>

       shall be made pursuant to Article 7.2. Any Party may change such address
       by notice given to the other Party in the manner set forth above.

13.9   Independent Contractors.  The relationship of the Parties to this CRADA
       is that of independent contractors and not agents of each other or joint
       venturers or partners. Each Party shall maintain sole and exclusive
       control over its personnel and operations. Collaborator employees who
       will be working at PHS facilities may be asked to sign a Guest Researcher
       or Special Volunteer Agreement appropriately modified in view of the
       terms of this CRADA.

13.10  Use of Name or Endorsements.  By entering into this CRADA, PHS does not
       directly or indirectly endorse any product or service provided, or to be
       provided, whether directly or indirectly related to either this CRADA or
       to any patent or other IP license or agreement which implements this
       CRADA by its successors, assignees, or licensees. The Collaborator shall
       not in any way state or imply that this CRADA is an endorsement of any
       such product or service by the U.S. Government or any of its
       organizational units or employees. Collaborator issued press releases
       that reference or rely upon the work of PHS under this CRADA shall be
       made available to PHS at least 7 days prior to publication for review and
       comment.

13.11  Exceptions to this CRADA.  Any exceptions or modifications to this CRADA
       that are agreed to by the Parties prior to their execution of this CRADA
       are set forth in Appendix C.

13.12  Reasonable Consent.  Whenever a Party's consent or permission is required
       under this CRADA, such consent or permission shall not be unreasonably
       withheld.

Article 14.  Duration of Agreement

14.1   Duration.  It is mutually recognized that the duration of this project
       cannot be rigidly defined in advance, and that the contemplated time
       periods for various phases of the RP are only good faith guidelines
       subject to adjustment by mutual agreement to fit circumstances as the RP
       proceeds. In no case will the term of this CRADA extend beyond the term
       indicated in the RP unless it is revised in accordance with Article 13.6.

14.2   Survivability.  The provisions of Articles 4.2, 5-8, 10.3-10.5, 11.1,
       12.2-12.4, 13.1, 13.10 and 14.2 shall survive the termination of this
       CRADA.





                       SIGNATURES BEGIN ON THE NEXT PAGE

                                       12
<PAGE>

FOR PHS:


 /s/ Alan Rabson                                           12/31/99
- ---------------------------------------------             ----------------------
Alan Rabson, M.D.                                         Date
Deputy Director, NCI

Mailing Address for Notices:

National Cancer Institute
Technology Development & Commercialization Branch
NCI-FCRDC
1003 West Seventh Street, Fairview Center, Suite 502
Frederick, MD 21701
phone: 301-846-5465
fax: 301-8466820

FOR THE COLLABORATOR:


 /s/ Russell J. Howard                                    2/24/00
- ---------------------------------------------             ----------------------
Russell J. Howard, Ph.D.                                  Date
CEO and President

Mailing Address for Notices:

Maxygen, Inc.
515 Galveston Drive
Redwood City, CA 94063
phone: 650-298-5300
fax: 650-364-2715

                                       13
<PAGE>

                          Appendix A: RESEARCH PLAN
                          -------------------------

Title: Shuffling of *******.

National Cancer Institute (NCI) Principal Investigators:
*******

*******

Collaborator Principal Investigator:
*******


          Term of CRADA: 3 years from execution of this CRADA.

A Letter of Intent (LOI) for this CRADA was executed by and between the Parties
on 10/13/99.

GOALS OF THE CRADA:
- ------------------

     This CRADA Research Plan (RP) describes a collaboration between the NCI-
Developmental Therapeutics Program (DTP) and Maxygen. The CRADA collaboration
leverages the NCI research on ******* and Maxygen's proprietary Shuffling
Technology which can rapidly evolve and select improved versions of natural and
synthetic *******. The major activity of this CRADA is for the DTP and Maxygen
to collaborate to screen and characterize ******* provided by Maxygen. The major
goal of this CRADA is to maximize the chemotherapeutic potential of *******.

Goal A of this CRADA is to screen and optimize evolved ******* synergize with
that of the commercially-available, tubulin inhibitor, *******, on breast cancer
cell lines.

The ******* provided by Maxygen for screening and optimization under this CRADA
will be targeted toward one or the other of the following improved cytotoxicity
and antigenic profiles:

(1) An evolved, *******.

(2) An evolved derivative of the *******.

One of the great attractions of ******* as anti-tumor agents is that they act by
mechanisms that are insensitive to mutations in *******. Additionally, they
synergize with the activity of DNA damaging agents such as ******* in some, but
not all, cell lines [32]. The Shuffled ******* may be expressed as fusions to
targeting domains such as *******.

                                      14
<PAGE>

Goal B: Implement an in vivo mouse model program to identify clinical candidates
from the optimized evolved *******.

Candidate molecules selected for improved activity from the efforts as described
in Goal A are to be screened by the NCI-Biological Testing Branch (BTB) in
******* animal models containing *******.

SCIENTIFIC BACKGROUND
- ---------------------

Maxygen's Shuffling Technology:

     Maxygen's Shuffling Technology: Maxygen's Shuffling Technology consists of
proprietary techniques, methodologies, processes, materials and/or
instrumentation useful for the recombination, rearrangement, and/or mutation of
genetic material for the creation of genetic diversity, and subsequent
techniques useful for the high-throughput (HTP) screening of the resultant
genetic material to identify potentially useful genes. Shuffling, as practiced
in the laboratory, mirrors the process of natural evolution by which the
tremendous diversity of all life forms may have been created. In nature, the
accumulation of mutations and the process of sexual reproduction creates genetic
diversity. This genetic diversity is subjected to natural selection pressures
such that only some of the genetic diversity survives. Humans have used the
enormous amount of existing genetic diversity to their advantage by breeding
domestic dogs, horses, cattle, cats, vegetables, fruits, and cereals from wild
breeding stocks. Breeders select whatever characteristics they desire from
within existing species and breed them together, regardless of whether the
resulting animal or plant would ever survive (i.e. be useful) in nature. In just
a few generations of breeding, substantial variation and novel properties can be
achieved.

     Shuffling is, in essence, the application of classical breeding principles
to sub-genomic sequences. This approach to sequence evolution generalizes
concepts from classical genetics, allowing one to selectively breed DNA
sequences in the test tube. Maxygen begins with the natural diversity already
present in a gene family or creates it by mutagenesis, and then rapidly shuffles
the diversity to create a large pool of novel genes. Their process involves
fragmenting the genes into pieces and reassembling them in a homology-dependent
fashion. Those genes that encode proteins with the desired novel properties are
then selected using high-throughput (HTP) screening assays. As with traditional
breeding, Maxygen's technology does not require a rational understanding of the
genes involved in order to engineer novel properties. This technology provides a
powerful tool for rapidly evolving single genes, operons and whole viruses for
desired properties, and has many advantages relative to random mutation or
rational sequence design.

*******

RELATED PATENT APPLICATIONS AND PATENTS, OTHER AGREEMENTS:
- ---------------------------------------------------------

                                      15
<PAGE>

The Parties hereby modify their rights under the following prior agreements:

Confidential Disclosure Agreement: Two-way agreement # 3-60778-99;

     *******.

     *******

*******

and the Parties agree that the materials and/or information provided thereunder
are now governed by the terms of this CRADA in accordance with Article 13.2,
except that the obligations of the parties with regard to confidentiality shall
remain retroactive to December 14, 1998.

Letter of Intent: A Letter of Intent (LOI) for this CRADA was executed by and
- ----------------
between the Parties on 10/13/99. With this exception, there are no other
existing CRADAs between NIH and Maxygen.

Related Patents/Patent Applications of NCI:
- ------------------------------------------

Note: Maxygen has decided not to apply for a license at this time for the NIH
Intellectual Property listed below. Maxygen would prefer to wait for results
obtained from the Research Plan of this CRADA before applying for a license.
Nothing herein is a commitment by NIH not to license this patent(s) to others
who may apply for a license pursuant to 37CFR 404 in the interim.

*******

                                      16
<PAGE>

                                  APPENDIX B
                                  ----------

FINANCIAL AND STAFFING CONTRIBUTIONS OF THE PARTIES
- ---------------------------------------------------

Maxygen Staffing: (total of 0.******* person-years for 1st year of CRADA.
Staffing in subsequent years 2-3 will be contingent on the results obtained in
the initial year). Changes in staffing levels will be documented by written
amendment.

Maxygen will provide scientific staff and other support as necessary to conduct
the research outlined in Appendix A, Research Plan. Staffing for the first year
will be as follows:

     Name      Position / title   % of time devoted to CRADA Research Plan
     --------------------------   ----------------------------------------

*******      Principal Investigator     *******

     Duties: Direct the research described in the CRADA goals and provide
scientific staff and other support as necessary to conduct the Research Plan as
outlined in Appendix A.

*******        Manager, Business Development      *******

     Duties: Assess commercial progress and opportunities, and provide on-going
business support for Research Plan activities.

*******        Maxygen   *******

     Duties: Creation of Shuffled ******* at Maxygen, and scale-up of
expression.

*******        Maxygen   *******

     Duties: Expression and HTP screening of *******.

The above assignments and time allocations are approximate. During the term of
the CRADA, these staffing assignments and percentages of time devoted to CRADA
research are likely to vary from the information provided above.

Maxygen Financial Support: No funding will be provided to the National Cancer
Institute for collaborative research and development pursuant to this CRADA.

National Cancer Institute Staffing: (total of ******* person-years/year).

                                      17
<PAGE>

Name                Position / title    % time devoted to CRADA Research
- ------------------------------------    --------------------------------

*******         NCI, Principal Investigator                 *******

     Duties: To direct the research described in the CRADA goals and provide
scientific staff and other support as necessary to conduct the Research Plan as
outlined in Appendix A.

*******         Principal Investigator                      *******

     Duties: To direct the research described in the CRADA goals and provide
scientific staff and other support as necessary to conduct the Research Plan as
outlined in Appendix A.

*******,       SAIC Investigator                            *******

     Duties: Supervise SAIC personnel on project and conduct in vitro assays.

*******        NCI/DTP / LDDR                               *******

     Duties: Conduct in vitro assays.

*******        NCI/DTP Investigator                         *******

     Duties: Conduct in vitro assays

*******        NCI/DTP Investigator                         *******

     Duties: Conduct in vivo assays

*******        SAIC Research Technician                     *******

     Duties: Conduct in vivo assays

NCI Financial Support:

NCI will provide no funding to the Collaborator for collaborative research and
development pursuant to this CRADA inasmuch as financial contributions by the
U.S. government to non-Federal parties under a CRADA are not authorized under
the Federal Technology Transfer Act [15 U.S.C. (S) 3710a(d)(1)].

                                      18
<PAGE>

                                  APPENDIX C
                                  ----------

                  EXCEPTIONS OR MODIFICATIONS TO THIS CRADA
                  -----------------------------------------

The PHS Model CRADA is replaced in its entirety by the following in which
additional terms are underlined, while deletions are struck-out.

                                      19
<PAGE>

                             PUBLIC HEALTH SERVICE

                COOPERATIVE RESEARCH AND DEVELOPMENT AGREEMENT

This Cooperative Research and Development Agreement, hereinafter referred to as
the CRADA, consists of this Cover Page, an attached Agreement, and various
Appendices referenced in the Agreement.

This Cover Page serves to identify the Parties to this CRADA:

     (1) the following Bureau(s), Institute(s), Center(s) or Division(s) of the
National Institutes of Health (`NIH'), The National Cancer Institute (`NCI'),
hereinafter referred to as the National Institutes of Health (`NIH'); and

     (2) Maxygen, Inc. which has offices at 515 Galveston Drive, Redwood City,
California 94063, hereinafter referred to as the `Collaborator'.

                                      20
<PAGE>

COOPERATIVE  RESEARCH AND DEVELOPMENT AGREEMENT


Article 1.  Introduction

This Cooperative Research and Development Agreement (CRADA) between NIH and the
Collaborator will be effective when signed by all Parties.  The research and
development activities which will be undertaken by each of the Parties in the
course of this CRADA are detailed in the Research Plan which is attached as
Appendix A.  The funding and staffing commitments of the Parties are set forth
in Appendix B.  Any exceptions or changes to the CRADA are set forth in Appendix
C.  This CRADA is made under the authority of the Federal Technology Transfer
Act, 15 U.S.C. (S)3710a and is governed by its terms.

Article 2.  Definitions

As used in this CRADA, the following terms shall have the indicated meanings:

2.1  "Affiliate" means any corporation or other business entity controlled by,
     controlling, or under common control with Collaborator. For this purpose, A
     "control" means direct or indirect beneficial ownership of at least fifty
     (50) percent of the voting stock or at least fifty (50) percent interest in
     the income of such corporation or other business.

2.2  "Cooperative Research and Development Agreement" or "CRADA" means this
     Agreement, entered into by NIH pursuant to the Federal Technology Transfer
     Act of 1986, as amended, 15 U.S.C. 3710a et seq. and Executive Order 12591
     of October 10, 1987.

2.3  "Government" means the Government of the United States as represented
     through the NIH agency that is a Party to this agreement.

2.4  "IP" means intellectual property.

2.5  "Invention" means any invention or discovery which is or may be
     patentable or otherwise protected under title 35, United States Code, or
     any novel variety or plant which is or may be protectable under the Plant
     Variety Protection Act (7 U.S.C. 2321 et seq.).

                                       21
<PAGE>

2.6  "Principal Investigator(s)" or "PIs" means the persons designated
     respectively by the Parties to this CRADA who will be responsible for the
     scientific and technical conduct of the Research Plan.

2.7  "Proprietary/Confidential Information" means confidential scientific,
     business, or financial information provided that such information does not
     include:

     2.7.1.  information that is publicly known or available from other sources
             who are not under a confidentiality obligation to the source of the
             information;

     2.7.2.  information which has been made available by its owners to others
             without a confidentiality obligation;

     2.7.3.  information which is already known by or available to the receiving
             Party without a confidentiality obligation; or

     2.7.4.  information which relates to potential hazards or cautionary
             warnings associated with the production, handling or use of the
             subject matter of the Research Plan of this CRADA.

2.8  "Research Materials" means all tangible materials other than Subject Data
     first produced in the performance of the Research Plan of this CRADA.

2.9  "Research Plan" means the statement in Appendix A of the respective
     research and development commitments of the Parties to this CRADA.

2.10 "Subject Invention" means any Invention of the Parties, conceived or first
     actually reduced to practice in the performance of the Research Plan of
     this CRADA.

2.11 "Subject Data" means all recorded information first produced in the
     performance of the Research Plan of this CRADA by the Parties.

2.12 "Steering Committee" means the joint NIH Collaborator research and
     development team whose composition and responsibilities with regard to the
     studies performed under this CRADA are described in Article 3.3 of this
     CRADA.

                                       22
<PAGE>

2.13 "Shuffling" means the systems set up by man to use high speed recombination
     and/or rearrangement and/or mutation of genetic material for the creation
     of genetic diversity.

2.14 "Shuffling Technology" means techniques, methodologies, processes,
     materials and/or instrumentation useful for Shuffling, and the screening of
     genetic material resulting from Shuffling to identify potential useful
     genes.

Article 3. Cooperative Research

3.1  Principal Investigators.  NIH research work under this CRADA will be
     performed by the NIH laboratory identified in the Research Plan, and the
     NIH Principal Investigator (PI) designated in the Research Plan will be
     responsible for the scientific and technical conduct of this project on
     behalf of NIH. Also designated in the Research Plan is the Collaborator PI
     who will be responsible for the scientific and technical conduct of this
     project on behalf of the Collaborator.

3.2  Research Plan Change.  The Research Plan may be modified by mutual written
     consent of the Principal Investigators. Substantial changes in the scope of
     the Research Plan will be treated as amendments under Article 13.6. If the
     results from the Research Plan are promising, NIH and Collaborator shall
     discuss, in good faith, plans to support and to submit proposals for
     further research in a separate clinical CRADA. If the Research Plan is
     amended to include the participation of any extramural grantee
     investigators, NIH shall urge the grantee investigators to cooperate
     exclusively with the Collaborator. However, such urging shall not
     constitute a condition of any grant award.

3.3  Steering Committee and CRADA Research. The Parties agree to establish a
     Steering Committee comprising at least the Principal Investigators
     designated pursuant to Article 3.1 to conduct and monitor the research in
     accordance with the Research Plan, review Subject Inventions disclosures
     and to review proposed publications and data. Details of the research and
     development as set forth in the Research Plan shall be formulated, reviewed
     and/or approved in Steering Committee meetings before implementation of any
     resource-intensive study. Notwithstanding the forgoing, Collaborator has
     the option to sponsor its own pre-clinical studies outside the scope of
     this CRADA.

3.4  Composition of Steering Committee. Collaborator and NIH shall have equal
     voice in decisions of the Steering Committee. The initial composition of
     the Steering Committee shall be voting members on behalf of NIH and two
     voting members on behalf of Collaborator. A Steering Committee member
     representing NIH will co-chair the Steering committee with the Steering
     Committee member representing Collaborator. The membership of the Steering
     Committee may be changed from time to time as mutually agreed by NIH and
     Collaborator in writing.

                                       23
<PAGE>

3.5  Meetings. The Steering Committee shall meet within one month of the
     execution of this CRADA, and then regularly once a quarter thereafter or as
     appropriate. The Steering Committee shall be the forum for discussion of
     issues for which differences in opinion may arise and shall be the initial
     forum to attempt to resolve any disputes arising therefrom. In the event,
     resolution of such dispute(s) is not achieved in the Steering Committee,
     the dispute resolution mechanism of Article 11 herein shall be implemented.
     The Principal Investigators shall report regularly to the Steering
     Committee on the progress of the research and development efforts covered
     by this CRADA, but not less than once a quarter, unless mutually agreed.
     Attendance at the Steering Committee meetings shall be limited to members
     of the Steering Committee and invited participants, as mutually agreed to
     by the Parties. Invited participants shall be non-voting members of the
     Steering Committee.

3.6  Written Record. The Steering Committee shall appoint one of its members to
     act as the Committee Secretary for each meeting, such appointment
     alternately between the parties from meeting to meeting. The Secretary
     shall prepare, for Committee approval and signature, written summaries of
     each Steering Committee meeting within two weeks of each Steering Committee
     meeting. These summaries shall include information about Steering
     Committee deliberations and describe issues addressed and decisions
     reached. Written materials created by the Steering Committee shall be
     treated as described in subarticle 3.7 below. The written summary shall be
     deemed to be deemed to be approved by the Committee if no comments are
     received within two weeks of receipt thereof. Upon incorporation of
     modifications in accordance with such comments, the revised summary shall
     be transmitted to Committee members of signature, but will be deemed
     approved within two weeks of receipt thereof.

3.7  Treatment of Steering Committee Proprietary Information. Except as required
     by law and subject to Article 8 of this CRADA, the Parties agree that
     Proprietary/Confidential Information including disclosures of such data in
     discussions and information exchanged at meetings of the Steering
     Committee, and in written summaries of Steering Committee meetings, shall
     be maintained as confidential to the Parties, and shall not be disclosed to
     any third parties without the consultation and written agreement within the
     Steering Committee.

 Article 4. Reports

 4.1 Interim Reports.  The Parties shall exchange formal written interim
     progress reports on a schedule agreed to by the PIs, but at least within
     twelve (12) months after this CRADA becomes effective and at least within
     every twelve (12) months thereafter.  Such reports shall set forth the
     technical progress made, identifying such problems as may have been
     encountered and establishing goals and objectives requiring further effort,
     any modifications to the Research Plan pursuant to Article 3.2, and all
     CRADA-related patent applications filed.

                                       24
<PAGE>

     Steering Committee reports or copies of annual reports updating the
     progress of the CRADA research shall satisfy the minimum reporting
     requirements under this Article 4.1.

4.2  Final Reports. The Parties shall exchange final reports of their results
     within four (4) months after completing the projects described in the
     Research Plan or after the expiration or termination of this CRADA.

Article 5.  Financial and Staffing Obligations

5.1  NIH and Collaborator Contributions.  The contributions of the Parties,
     including payment schedules, if applicable, are set forth in Appendix B.
     NIH shall not be obligated to perform any of the research specified herein
     or to take any other action required by this CRADA if the funding is not
     provided as set forth in Appendix B.  NIH shall return excess funds to the
     Collaborator when it sends its final fiscal report pursuant to Article 5.2,
     except for staffing support pursuant to Article 10.3.  Collaborator
     acknowledges that the U.S. Government will have the authority to retain and
     expend any excess funds for up to one (1) year subsequent to the expiration
     or termination of the CRADA to cover any costs incurred during the term of
     the CRADA in undertaking the work set forth in the Research Plan.

5.2  Accounting Records. NIH shall maintain separate and distinct current
     accounts, records, and other evidence supporting all its obligations under
     this CRADA, and shall provide the Collaborator a final fiscal report
     pursuant to Article 4.2.

5.3  Capital Equipment. Equipment purchased by NIH with funds provided by the
     Collaborator shall be the property of NIH.  All capital equipment provided
     under this CRADA by one party for the use of another Party remains the
     property of the providing Party unless other disposition is mutually agreed
     upon by in writing by the Parties.  If title to this equipment remains with
     the providing Party, that Party is responsible for maintenance of the
     equipment and the costs of its transportation to and from the site where it
     will be used.

Article 6.  Intellectual Property Rights and Patent Applications

6.1  Reporting. The Parties shall promptly report to each other in writing each
     Subject Invention resulting from the research conducted under this CRADA
     that is reported to them by their respective employees. Each Party shall
     report all Subject Inventions to the other Party in sufficient detail to
     determine inventorship. Such reports shall be treated as
     Proprietary/Confidential Information in accordance with Article 8.4.

                                       25
<PAGE>

6.2  Collaborator Employee Inventions. If the Collaborator does not elect to
     retain title to its IP rights in a Subject Invention, the Collaborator
     shall offer to assign these IP rights to the Subject Invention to NIH
     pursuant to Article 6.5. If NIH declines such assignment, the Collaborator
     may release title to its IP rights as it may determine.

6.3  NIH Employee Inventions. NIH on behalf of the U.S. Government may elect to
     retain title to its IP rights to each Subject Invention made solely by NIH
     employees. If NIH does not elect to retain title to its IP rights, NIH
     shall offer to assign these IP rights to such Subject Invention to the
     Collaborator pursuant to Article 6.5. If the Collaborator declines such
     assignment, NIH may release title to its IP rights in such Subject
     Invention to its employee inventors pursuant to Article 6.6.

6.4  Joint Inventions.  Each Subject Invention made jointly by NIH and
     Collaborator employees shall be jointly owned by NIH and the Collaborator.
     If NIH and Collaborator both agree that a patent application should be
     filed on a jointly owned Subject Invention, then the parties shall consult
     about the best manner to proceed in filing and prosecuting the jointly
     owned patent application. If NIH and Collaborator elect to file jointly,
     then each shall bear one-half the costs of such filing and prosecution.
     However, NIH only has authority to reimburse such costs directly to law
     firms under contract to NIH. Alternatively, the Collaborator may elect to
     file the joint patent or other IP application(s) thereon and shall notify
     NIH promptly upon making this election. If the Collaborator decides to file
     such applications, it shall do so in a timely manner and at its own
     expense. If the Collaborator does not elect to file such application(s),
     NIH on behalf of the U.S. Government shall have the right to file the joint
     application(s) in a timely manner and at its own expense. If either Party
     decides not to retain title to its IP rights to a jointly owned Subject
     Invention, it shall offer to assign such rights to the other Party pursuant
     to Article 6.5. If the other Party declines such assignment, the offering
     Party may release title to its IP rights as provided in Articles 6.2, 6.3,
     and 6.6.

6.5  Filing of Patent Applications.  With respect to Subject Inventions made by
     the Collaborator as described in Article 6.2, or by NIH as described in
     Article 6.3, a Party exercising its right to elect to retain title to its
     IP rights to a Subject Invention agrees to file patent or other IP
     applications in a timely manner and at its own expense and after
     consultation with the other Party. The Party shall notify the other Party
     of its decision regarding filing in countries other than the United States
     in a timely manner. The Party may elect not to file a patent or other IP
     application thereon in any particular country or countries provided it so
     advises the other Party ninety (90) days prior to the expiration of any
     applicable filing deadline, priority period or statutory bar date, and
     hereby agrees to assign its IP right, title and interest in the Subject
     Invention in such country or countries to the Subject Invention to the
     other Party and to cooperate in the preparation and filing of a patent or
     other IP applications. In any countries in which title to patent or other
     IP rights for Subject Inventions is transferred to the Collaborator, the
     Collaborator agrees that NIH

                                       26
<PAGE>

     inventors will share in any royalty distribution that the Collaborator pays
     to its own inventors.

6.6  Release to Inventors.  In the event neither of the Parties to this CRADA
     elects to file a patent or other IP application on a Subject Invention,
     either or both (if a joint invention) may retain or release titles to their
     IP rights in accordance with their respective policies and procedures. If
     NIH elects not to retain title to its IP rights in and to any such Subject
     Invention made solely or jointly by NIH, the Government shall retain a
     nonexclusive, non-transferable, irrevocable, royalty-free license to
     practice any such Subject Invention, or have it practiced throughout the
     world by or on behalf of the Government. Similarly, if Collaborator elects
     not to retain title to any IP rights to Subject Inventions made jointly or
     solely by its employees and, pursuant to Article 6.2 herein, offers such
     rights to NIH which waives such rights, then Collaborator shall be free to
     release such rights to its employee inventors subject to the Government
     retaining a nonexclusive, non-transferable, irrevocable, royalty-free
     license to practice, or have such Subject Inventions(s) practiced
     throughout the world by or on behalf of the Government.

6.7  Patent Expenses. The expenses attendant to the filing of patent or other
     IP applications generally shall be paid by the Party filing such
     application unless agreed otherwise in connection with jointly owned patent
     applications. If an exclusive license to any Subject Invention is granted
     to the Collaborator, the Collaborator shall be responsible for all past and
     future out-of-pocket expenses in connection with the preparation, filing,
     prosecution and maintenance of any applications claiming such exclusively-
     licensed inventions and any patents or other IP grants that may issue on
     such applications. The Collaborator may waive its exclusive license rights
     on any application, patent or other IP grant at any time, and incur no
     subsequent compensation obligation for that application, patent or IP
     grant.

6.8  Prosecution of Intellectual Property Applications.  Within one month of
     receipt or filing,  each Party shall provide the other Party with copies of
     the applications and all documents received from or filed with the relevant
     patent or other IP office in connection with the prosecution of such
     applications.  Each Party shall also provide the other Party with the power
     to inspect and make copies of all documents retained in the patent or other
     IP application files by the applicable patent or other IP office.  Where
     licensing is contemplated by Collaborator, the Parties agree to consult
     with each other with respect to the prosecution of applications for NIH
     Subject Inventions described in Article 6.3 and joint Subject Inventions
     described in Article 6.4. If the one party elects to file and prosecute IP
     applications on joint Subject Inventions pursuant to Article 6.4, the other
     party will be granted an associate power of attorney (or its equivalent) on
     such IP applications. Patent counsel for each party shall cooperate with
     patent counsel for the other party in connection with the filing,
     prosecution and maintenance of patent applications claiming joint Subject
     Inventions. Associate power of Attorney will not be used by either party to
     make any submissions to the USPTO without consulting with the other party.

                                       27
<PAGE>

Article 7.  Licensing

7.1  Option for Commercialization License. With respect to Government IP rights
     to any Subject Invention not made solely by the Collaborator's employees
     for which a patent or other IP application is filed, NIH hereby grants to
     the Collaborator an exclusive option to elect an exclusive or nonexclusive
     commercialization license, which is substantially in the form of the
     appropriate model NIH license agreement. This option does not apply to
     Subject Inventions conceived prior to the effective date of this CRADA that
     are reduced to practice under this CRADA, if prior to that reduction to
     practice, NIH has filed a patent application on the invention and has
     licensed it or offered to license it to a third party. The terms of the
     license will fairly reflect the nature of the invention, the relative
     contributions of the Parties to the invention and the CRADA, the risks
     incurred by the Collaborator and the costs of subsequent research and
     development needed to bring the invention to the marketplace. The field of
     use of the license will be commensurate with the scope of the Research
     Plan. The Collaborator shall have the right to sublicense the license
     rights granted hereunder, provided that the Collaborator obtains the prior
     written consent of NIH for the sublicensing of its non-exclusive license
     rights, such consent to be reasonably given in situations where
     Collaborator sublicenses its exclusive rights in one or more Subject
     Inventions(s) to sublicensee(s) and requests to sublicense its non-
     exclusive rights in Subject Invention(s) to the same sublicensee(s); and
     any such sublicensee shall be bound by the terms of this license.

7.2  Exercise of License Option.  The option of Article 7.1 must be exercised
     with respect to a particular Subject Invention by written notice mailed
     within three (3) months after either (i) Collaborator receives written
     notice from NIH that the patent or other IP application has been filed; or
     (ii) the date Collaborator files such IP application. Exercise of this
     option by the Collaborator initiates a negotiation period that expires nine
     (9) months after the exercise of the option. If the last proposal by the
     Collaborator has not been responded to in writing by NIH within this nine
     (9) month period, the negotiation period shall be extended to expire one
     (1) month after NIH so responds, during which month the Collaborator may
     accept in writing the final license proposal of NIH. In the absence of such
     acceptance, or an extension of the time limits by NIH, NIH will be free to
     license its rights in such Subject Invention to others. In the event that
     the Collaborator elects the option for an exclusive license, but no such
     license is executed during the negotiation period, NIH agrees not to make
     an offer for an exclusive license on more favorable terms to a third party
     for a period of twelve (12) months without first offering Collaborator
     those more favorable terms. These times may be extended at the sole
     discretion of NIH upon good cause shown in writing by the Collaborator.

                                       28
<PAGE>

7.3  License for NIH Employee Inventions and Joint Inventions.  Pursuant to 15
     U.S.C. (S) 3710a(b)(1)(A), for Subject Inventions made under this CRADA by
     a NIH employee(s) or jointly by such employee(s) and employees of the
     Collaborator pursuant to Articles 6.3 and 6.4 and licensed pursuant to the
     option of Article 7.1, the Collaborator grants to the Government a
     nonexclusive, nontransferable, irrevocable, paid-up license to practice the
     invention or have the invention practiced throughout the world by or on
     behalf of the Government.  In the exercise of such license, the Government
     shall not publicly disclose trade secrets or commercial or financial
     information that is privileged or confidential within the meaning of 5
     U.S.C. 552(b)(4) or which would be considered as such if it had been
     obtained from a non-Federal party. The retained non-exclusive Government
     licenses described in this Article 7, and elsewhere herein, are intended by
     the NIH to be invoked by the NIH in circumstances consistent with the
     legislative history of the Stevenson-Wydler Technology Innovation Act, as
     amended, that provide for such licenses.

7.4  License in Collaborator Inventions.  Pursuant to 15 U.S.C. (S) 3710a(b)(2),
     for inventions made solely by Collaborator employees under this CRADA
     pursuant to Article 6.2, (1) NIH hereby ensures Collaborator that
     Collaborator shall retain title in such Subject Inventions, and (2) the
     Collaborator grants to the Government a nonexclusive, nontransferable,
     irrevocable, paid-up license to practice the Subject invention or have the
     Subject Invention practiced throughout the world by or on behalf of the
     Government for research or other Government purposes. As stated in the
     Research Plan, during the course and in the performance of this CRADA, the
     Collaborator will only use Shuffling Technology that Collaborator has
     developed or develops outside the course and performance of the CRADA
     program. If the progress of the CRADA research would benefit by the
     development of inventive Shuffling Technology subject matter during the
     course of the CRADA, Collaborator will attempt to develop such inventive
     subject matter outside the scope, course and performance of the present
     CRADA. Such inventive Shuffling Technology subject matter shall not be
     considered to comprise a Subject Invention as defined herein. However,
     selected Shuffled ******* and their corresponding DNA clones are considered
     Research Materials of the CRADA and fall under the scope of the CRADA
     Research Plan.

7.5  Third Party License.  Pursuant to 15 U.S.C. (S) 3710a(b)(1)(B), if NIH
     grants an exclusive license to a Subject Invention made wholly by NIH
     employees or jointly with a Collaborator under this CRADA, pursuant to
     Articles 6.3 and 6.4, the Government shall retain the right to require the
     Collaborator to grant to a responsible applicant a nonexclusive, partially
     exclusive, or exclusive sublicense to use the invention in Collaborator's
     licensed field of use on terms that are reasonable under the circumstances;
     or if the Collaborator fails to grant such a license, to grant the license
     itself.  The exercise of such rights by the Government shall only be in
     exceptional circumstances and only if the Government determines (i) the
     action is necessary to meet health or safety needs that are not reasonably
     satisfied by Collaborator, (ii) the action is necessary to meet
     requirements

                                       29
<PAGE>

     for public use specified by Federal regulations, and such requirements are
     not reasonably satisfied by the Collaborator; or (iii) the Collaborator has
     failed to comply with an agreement containing provisions described in 15
     U.S.C. 3710a(c)(4)(B). The determination made by the Government under this
     Article is subject to administrative appeal and judicial review under 35
     U.S.C. 203(2).

7.6  Joint Inventions Not Exclusively Licensed.  In the event that the
     Collaborator does not acquire an exclusive commercialization license to IP
     rights in all fields in joint Subject Inventions described in Article 6.4,
     then each Party shall have the right to use the joint Subject Invention and
     to license its use to others in all fields not exclusively licensed to
     Collaborator.  The Parties may agree to a joint licensing approach for such
     IP rights.

Article 8.  Proprietary Rights and Publication

8.1  Right of Access.  NIH and the Collaborator agree to exchange all Subject
     Data produced in the course of research under this CRADA.  Research
     Materials will be shared equally by the Parties to the CRADA unless other
     disposition is agreed to by the Parties.  All Parties to this CRADA will be
     free to utilize Subject Data and Research Materials for their own purposes,
     consistent with their obligations under this CRADA provided that NIH shall
     not have direct access to and/or direct use of Collaborator's proprietary
     Shuffling Technology in the performance of the CRADA.

8.2  Ownership of Subject Data and Research Materials.  Subject to the sharing
     requirements of Paragraph 8.1 and the regulatory filing requirements of
     Paragraph 8.3, the producing Party will retain ownership of and title to
     all Subject Inventions, all Subject Data and all Research Materials
     produced solely by their investigators.  Jointly developed Subject
     Inventions, Subject Data and Research Materials will be jointly owned.

8.3  Dissemination of Subject Data and Research Materials.  To the extent
     permitted by law, the Collaborator and NIH agree to use reasonable efforts
     to keep Subject Data and Research Materials confidential until published or
     until corresponding patent applications are filed.  Any information that
     would identify human subjects of research or patients will always be
     maintained confidentially.  To the extent permitted by law, the
     Collaborator shall have the exclusive right to use any and all CRADA
     Subject Data in and for any regulatory filing by or on behalf of
     Collaborator, except that NIH shall have the exclusive right to use Subject
     Data for that purpose, and authorize others to do so, if Collaborator
     abandons its commercialization efforts.

8.4  Proprietary/Confidential Information.  Each Party agrees to limit its
     disclosure of Proprietary/Confidential Information to the other Party
     hereunder to the amount necessary

                                       30
<PAGE>

                                                                    CRADA #00880
     to carry out the Research Plan of this CRADA, and shall place a
     confidentiality notice on all such information. Confidential oral
     communications shall be reduced to writing within 30 days by the disclosing
     Party. Each Party receiving Proprietary/Confidential Information of the
     other Party pursuant to this CRADA agrees that any information so
     designated shall be used by it only for the purposes described in the
     attached Research Plan. Any Party may object to the designation of
     information as Proprietary/Confidential Information by another Party.
     Subject Data and Research Materials developed solely by the Collaborator
     may be designated as Proprietary/Confidential Information when they are
     wholly separable from the Subject Data and Research Materials developed
     jointly with NIH investigators, and advance designation of such data and
     material categories is set forth in the Research Plan. The exchange of
     other confidential information, e.g., patient-identifying data, should be
     similarly limited and treated. Jointly developed Subject Data and Research
     Material derived from the Research Plan may be disclosed by Collaborator to
     a third party under a confidentiality agreement for the purpose of possible
     sublicensing pursuant to any licensing agreement of Subject Inventions or
     such purposes as Collaborator considers appropriate to pursue its
     commercial interests including, but not limited to, disclosures to
     manufacturing subcontractors, clinical or preclinical laboratories, medical
     or scientific consultants, quality control, quality assurance or analytical
     laboratories, or government regulatory agencies.


8.5  Protection of Proprietary/Confidential Information.
     Proprietary/Confidential Information shall not be disclosed, copied,
     reproduced or otherwise made available to any other person or entity
     without the consent of the owning Party except as required under court
     order or the Freedom of Information Act (5 U.S.C. (S) 552). Each Party
     agrees to use its best efforts to maintain the confidentiality of
     Proprietary/Confidential Information. Each Party agrees that the other
     Party is not liable for the disclosure of Proprietary/Confidential
     Information which, after notice to and consultation with the concerned
     Party, the other Party in possession of the Proprietary/Confidential
     Information determines may not be lawfully withheld, provided the concerned
     Party has been given an opportunity to seek a court order to enjoin
     disclosure.


8.6  Duration of Confidentiality Obligation. The obligation to maintain the
     confidentiality of Proprietary/Confidential Information shall expire at the
     earlier of the date when the information is no longer Proprietary
     Information as defined in Article 2.7 or three (3) years after the
     expiration or termination date of this CRADA unless, after the said three
     (3) years, any Party informs the other Party that the Confidential
     Information is still secret and confidential, in which case the obligation
     shall extend for a further successive periods of two (2) years. The
     Collaborator may request an extension to these terms when necessary to
     protect Proprietary/Confidential Information relating to products not yet
     commercialized.


8.7  Publication. The Parties are encouraged to make publicly available the
     results of their research. Before either Party submits a paper or abstract
     for publication or otherwise intends to publicly disclose information about
     a Subject Invention, Subject Data or

                                       31
<PAGE>

Research Materials, or any other confidential information concerning this
CRADA, the submitting Party shall first submit a draft of the proposed
disclosure to the Steering Committee for review at least 30 days prior to any
submission for publication or other public disclosure. As defined under Article
8.4, if such proposed disclosure contains Proprietary/Confidential Information
of a Party, such Party may require that such Confidential Information be deleted
or modified from the proposed disclosure in accordance with Article 8.5. The
Steering Committee shall provide advisory review and comments prior to
submission of proposed disclosures for publication and/or public presentation.
The submitting party will seriously consider the suggested modifications of the
Steering Committee. To avoid loss of patent rights as a result of premature
public disclosure of patentable information, the reviewing Party shall notify
the submitting Party in writing within 30 days after receipt of such proposed
disclosure whether the reviewing Party desires that a patent application be
filed on any invention disclosed in such proposed disclosure. In the event that
the reviewing Party desires such filing, the submitting Party shall withhold
publication or disclosure of such proposed disclosure until the earlier of: (i)
the date a patent application is filed thereon, or (ii) the date the Parties
determine after consultation that no patentable invention exists, or (iii) 60
days after receipt by the submitting Party of the reviewing Party's written
notice of its desire to file such patent application.


Article 9.  Representations and Warranties

9.1  Representations and Warranties of NIH. NIH hereby represents and warrants
     to the Collaborator that the official signing this CRADA has authority to
     do so.

9.2  Representations and Warranties of the Collaborator.

     (a)  The Collaborator hereby represents and warrants to NIH that the
          Collaborator has the requisite power and authority to enter into this
          CRADA and to perform according to its terms, and that the
          Collaborator's official signing this CRADA has authority to do so.
          The Collaborator further represents that it is financially able to
          satisfy any funding commitments made in Appendix B.

     (b)  The Collaborator certifies that the statements herein are true,
          complete, and accurate to the best of its knowledge. The Collaborator
          is aware that any false, fictitious, or fraudulent statements or
          claims may subject it to criminal, civil, or administrative penalties.

9.3  NIH Disclosure of Third Party Rights. NIH hereby acknowledges that Research
     Materials provided to Collaborator during the course of the CRADA research
     may be

                                       32
<PAGE>

     subject to third party patent and other rights. NIH will exercise its best
     efforts to provide Collaborator with all non-privileged and
     non-confidential information its PI and NIH have in their possession, or of
     which they are aware, identifying third party rights in and to Research
     Materials supplied by NIH to Collaborator under this CRADA.


Article 10.  Termination

10.1 Termination By Mutual Consent. NIH and the Collaborator may terminate this
     CRADA, or portions thereof, at any time by mutual written consent.  In such
     event the Parties shall specify the disposition of all property,
     inventions, patent or other IP applications and other results of work
     accomplished or in progress, arising from or performed under this CRADA,
     all in accordance with the rights granted to the Parties under the terms of
     this Agreement.

10.2 Unilateral Termination. Either NIH or the Collaborator may unilaterally
     terminate this entire CRADA at any time by giving written notice at least
     thirty (30) days prior to the desired termination date, and any rights
     accrued in property, patents or other IP rights shall be disposed of as
     provided in paragraph 10.1, provided that, if either Party unilaterally
     terminates this CRADA for reasons other than for cause including, but not
     limited to, lack of interest, unwillingness or inability of either Party to
     contribute resources to the continuation of the CRADA research, and decides
     not to retain title to its IP rights to Subject Inventions, then pursuant
     to Articles 6.2, 6.3 and 6.4, such Party shall offer to assign these IP
     rights to such Subject Inventions to the other Party.

10.3 Staffing. If this CRADA is mutually or unilaterally terminated by
     Collaborator prior to its expiration, funds will nevertheless remain
     available to NIH for continuing any staffing commitment made by the
     Collaborator pursuant to Article 5.1 above and Appendix B, if applicable,
     for a period of six (6) months after such termination. If there are
     insufficient funds to cover this expense, the Collaborator agrees to pay
     the difference.

10.4 New Commitments. No Party shall make new commitments related to this CRADA
     after a mutual termination or notice of a unilateral termination and shall,
     to the extent feasible, cancel all outstanding commitments and contracts by
     the termination date.

10.5 Termination Costs.

                                       33
<PAGE>

     Collaborator shall not be responsible to NIH for any termination costs.

Article 11. Disputes

11.1 Settlement. Any dispute arising under this CRADA which is not disposed of
     by agreement of the Principal Investigators shall be submitted jointly to
     the signatories of this CRADA. If the signatories are unable to jointly
     resolve the dispute within thirty (30) days after notification thereof, the
     Assistant Secretary for Health (or his/her designee or successor) shall
     propose a resolution. Nothing in this Article shall prevent any Party from
     pursuing any additional administrative remedies that may be available and,
     after exhaustion of such administrative remedies, pursuing all available
     judicial remedies.

11.2 Continuation of Work. Pending the resolution of any dispute or claim
     pursuant to this Article, the Parties agree that performance of all
     non-disputed obligations shall be pursued diligently in accordance with the
     direction of the NIH signatory. Disputed obligations shall be pursued
     diligently by each Party in accordance with their best judgment and subject
     to their obligation to mitigate any damages resulting from their actions.

Article 12. Liability

12.1 Property. The U.S. Government shall not be responsible for damages to any
     Collaborator property  provided to NIH, where Collaborator retains title to
     the property, or any property acquired by Collaborator for its own use
     pursuant to this CRADA.

12.2 NO WARRANTIES. EXCEPT AS SPECIFICALLY STATED IN ARTICLE 9, THE PARTIES
     MAKE NO EXPRESS OR IMPLIED WARRANTY AS TO ANY MATTER WHATSOEVER, INCLUDING
     THE CONDITIONS OF THE RESEARCH OR ANY INVENTION OR PRODUCT, WHETHER
     TANGIBLE OR INTANGIBLE, MADE, OR DEVELOPED UNDER THIS CRADA, OR THE
     OWNERSHIP, MERCHANTABILITY, OR FITNESS FOR A PARTICULAR PURPOSE OF THE
     RESEARCH OR ANY INVENTION OR PRODUCT.

12.3 Indemnification. The Collaborator agrees to hold the U.S. Government
     harmless and to indemnify the Government for all liabilities, demands,
     damages, expenses and losses arising out of the use by the Collaborator for
     any purpose of the Subject Data, Research Materials and/or Subject
     Inventions produced in whole or part by NIH employees under this CRADA,
     unless due to the negligence or willful misconduct or willful
     misrepresentation of NIH, its employees, or agents. The Collaborator shall
     be liable

                                       34
<PAGE>

     for any claims or damages arising from the liable acts of the Collaborator
     in connection with this CRADA.  NIH has no authority to indemnify
     the Collaborator.

12.4 Force Majeure. Neither Party shall be liable for any unforeseeable event
     beyond its reasonable control not caused by the fault or negligence of such
     Party, which causes such Party to be unable to perform its obligations
     under this CRADA, and which it has been unable to overcome by the exercise
     of due diligence. In the event of the occurrence of such a force majeure
     event, the Party unable to perform shall promptly notify the other Party.
     It shall further use its best efforts to resume performance as quickly as
     possible and shall suspend performance only for such period of time as is
     necessary as a result of the force majeure event.


Article 13. Miscellaneous

13.1 Governing Law. The construction, validity, performance and effect of this
     CRADA shall be governed by Federal law, as applied by the Federal Courts in
     the District of Columbia. Federal law and regulations will preempt any
     conflicting or inconsistent provisions in this CRADA.

13.2 Entire Agreement. This CRADA constitutes the entire agreement between the
     Parties concerning the subject matter of this CRADA and supersedes any
     prior understanding or written or oral agreement.

     The Parties hereby modify their rights under the following prior
     agreement(s):

     Confidential Disclosure Agreement: Two-way agreement # 3-60778-99:

     *******

     Effective date: December 14, 1998

     Material Transfer Agreement: # 2-50178

     Provider: Maxygen; Recipient: NCI, DTP

     *******

     Executed: October xx, 1999; expiration date: October xx, 2002.

     and the Parties agree that the information provided thereunder is now
     governed by the terms of this CRADA.

13.3 Headings. Titles and headings of the articles and subarticles of this
     CRADA are for convenient reference only, do not form a part of this CRADA,
     and shall in no way affect its interpretation. The NIH component that is
     the Party for all purposes of this CRADA is the Bureau(s), Institute(s),
     Center(s) or Division(s) listed on the Cover Page herein.

                                       35
<PAGE>

13.4 Waivers. None of the provisions of this CRADA shall be considered waived by
     any Party unless such waiver is given in writing to the other Party. The
     failure of a Party to insist upon strict performance of any of the terms
     and conditions hereof, or failure or delay to exercise any rights provided
     herein or by law, shall not be deemed a waiver of any rights of any Party.

13.5 Severability. The illegality or invalidity of any provisions of this CRADA
     shall not impair, affect, or invalidate the other provisions of this CRADA.

13.6 Amendments. If either Party desires a modification to this CRADA, the
     Parties shall, upon reasonable notice of the proposed modification or
     extension by the Party desiring the change, confer in good faith to
     determine the desirability of such modification or extension. Such
     modification shall not be effective until a written amendment is signed by
     the signatories to this CRADA or by their representatives duly authorized
     to execute such amendment.

13.7 Assignment.  Neither this CRADA nor any rights or obligations of any Party
     hereunder shall be assigned or otherwise transferred by either Party
     without the prior written consent of the other Party, provided that a Party
     may assign its rights and obligations under this CRADA without such consent
     to an Affiliate or a third party that succeeds to substantially all of the
     business or assets of the assigning Party, by way of merger, sale of assets
     or otherwise.

13.8 Notices. All notices pertaining to or required by this CRADA shall be in
     writing and shall be signed by an authorized representative and shall be
     delivered by hand or sent by certified mail, return receipt requested, with
     postage prepaid, to the addresses indicated on the signature page for each
     Party. Notices regarding the exercise of license options shall be made
     pursuant to Article 7.2. Any Party may change such address by notice given
     to the other Party in the manner set forth above.

13.9 Independent Contractors. The relationship of the Parties to this CRADA is
     that of independent contractors and not agents of each other or joint
     venturers or partners. Each Party shall maintain sole and exclusive control
     over its personnel and operations. Collaborator employees who will be
     working at NIH facilities may be asked to sign a Guest Researcher or
     Special Volunteer Agreement appropriately modified in view of the terms of
     this CRADA.

13.10Use of Name or Endorsements. By entering into this CRADA, NIH does not
     directly or indirectly endorse any product or service provided, or to be
     provided, whether directly or

                                       36
<PAGE>

       indirectly related to either this CRADA or to any patent or other IP
       license or agreement which implements this CRADA by its successors,
       assignees, or licensees. The Collaborator shall not in any way state or
       imply that this CRADA is an endorsement of any such product or service by
       the U.S. Government or any of its organizational units or employees.
       Collaborator issued press releases that reference or rely upon the work
       of NIH under this CRADA shall be made available to NIH at least 7 days
       prior to publication for review and comment.

13.11  Exceptions to this CRADA. Any exceptions or modifications to this CRADA
       that are agreed to by the Parties prior to their execution of this CRADA
       are set forth in Appendix C.

13.12  Reasonable Consent. Whenever a Party's consent or permission is required
       under this CRADA, such consent or permission shall not be unreasonably
       withheld.

Article 14. Duration of Agreement

14.1   Duration. It is mutually recognized that the duration of this project
       cannot be rigidly defined in advance, and that the contemplated time
       periods for various phases of the Research Plan are only good faith
       guidelines subject to adjustment by mutual agreement to fit circumstances
       as the Research Plan proceeds. In no case will the term of this CRADA
       extend beyond the term indicated in the Research Plan unless it is
       revised in accordance with Article 13.6.

14.2   Survivability. The provisions of Articles 4.2, 5-8, 10.3-10.5, 11.1,
       12.2-12.4, 13.1, 13.10 and 14.2 shall survive the termination of this
       CRADA.


                       SIGNATURES BEGIN ON THE NEXT PAGE

FOR NIH:


________________________________________         Date:_______________________
Alan Rabson, M.D.
Deputy Director, NCI

Mailing Address for Notices:

                                       37
<PAGE>

National Cancer Institute

Technology Development & Commercialization Branch

NCI-FCRDC

1003 West Seventh Street,

Fairview Center, Suite 502

Frederick, MD 21701

Phone: 301-846-5465
Fax:   301-8466820


FOR THE COLLABORATOR:


_______________________________________           Date:_______________________

_______________________________________


Mailing Address for Notices:


__________________________________________________________

__________________________________________________________

__________________________________________________________

__________________________________________________________

__________________________________________________________

                                       38

<PAGE>

                                                                    EXHIBIT 23.1

              CONSENT OF ERNST & YOUNG LLP, INDEPENDENT AUDITORS

We consent to the reference to our firm under the captions "Selected Financial
Data" and "Experts" and to the use of our report dated February 18, 2000, in
the Registration Statement (Form S-1) and related Prospectus of Maxygen, Inc.
for the registration of 1,725,000 shares of its common stock.


                                                  /s/ Ernst & Young LLP

Palo Alto, California
March 2, 2000

<TABLE> <S> <C>

<PAGE>

<ARTICLE> 5
<LEGEND>
THIS SCHEDULE CONTAINS SUMMARY FINANCIAL INFORMATION EXTRACTED FROM THE AUDITED
CONSOLIDATED FINANCIAL STATEMENTS AS OF AND FOR THE YEAR ENDED DECEMBER 31,
1999.
</LEGEND>
<MULTIPLIER> 1,000

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<FISCAL-YEAR-END>                          DEC-31-1999
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<CASH>                                         136,343
<SECURITIES>                                         0
<RECEIVABLES>                                    3,038
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<CURRENT-ASSETS>                               140,181
<PP&E>                                           5,711
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<TOTAL-ASSETS>                                 145,578
<CURRENT-LIABILITIES>                            7,671
<BONDS>                                              0
                                0
                                          0
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<OTHER-SE>                                     133,713
<TOTAL-LIABILITY-AND-EQUITY>                   145,578
<SALES>                                              0
<TOTAL-REVENUES>                                14,017
<CGS>                                                0
<TOTAL-COSTS>                                        0
<OTHER-EXPENSES>                                26,748
<LOSS-PROVISION>                                     0
<INTEREST-EXPENSE>                                  58
<INCOME-PRETAX>                                 13,518
<INCOME-TAX>                                         0
<INCOME-CONTINUING>                             13,518
<DISCONTINUED>                                       0
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<EPS-BASIC>                                     (0.74)
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