Exhibit 4.2

                         REGISTRATION RIGHTS AGREEMENT


     THIS REGISTRATION RIGHTS AGREEMENT is made and entered into as of the 14th
day of March, 1997, by and between Maxygen, Inc., a Delaware corporation (the
"Company"), and the undersigned holders (the "Investors") of the Company's
Series A Preferred Stock, $0.0001 par value per share (the "Series A
Preferred"), and of the Company's Common Stock, $0.0001 par value per share (the
"Common Stock"). The term "Company Stock" shall mean the Common Stock and the
Series A Preferred.

                                    RECITALS
                                    --------

     The Company and the Investors have entered into that certain Securities
Purchase Agreement dated as the date hereof (the "Purchase Agreement") that
provides for the sale by the Company to the Investors of shares of Company Stock
and in connection with such sale, the Investors are to receive certain
registration rights with respect to such Company Stock

     NOW, THEREFORE, in consideration of the promises, mutual covenants and
conditions herein contained, and of other good and valuable consideration, the
receipt and sufficiency of which are hereby acknowledged, the parties hereby
agree as follows:

     1.  Definitions.  For purposes of this Agreement, the following terms shall
         -----------
have the following respective meanings:

     (a) "Act" shall mean the Securities Act of 1933, as amended, or any similar
federal statute enacted hereafter, and the rules and regulations of the
Commission thereunder, all as the same shall be in effect from time to time;

     (b) "Commission" shall mean the Securities and Exchange Commission or any
other federal agency at the time administering the Act;

     (c) The terms "register," "registered" and "registration" refer to a
registration effected by preparing and filing a registration statement in
compliance with the Act and the declaration or ordering of effectiveness of such
registration statement by the Commission;

     (d) "Registrable Securities" shall mean (i) shares of Common Stock issued
or issuable upon conversion of the Series A Preferred; (ii) shares of Common
Stock held of record by any of the Investors, and (iii) shares of Common Stock
issued as a


dividend or distribution with respect to, or in exchange or in replacement of,
the foregoing;

     (e) "Holder" shall mean an Investor if the Investor holds Registrable
Securities and any other person holding Registrable Securities to whom
registration rights have been transferred pursuant to Section 14 of this
Agreement; provided, however, that any person who acquires any of the
Registrable Securities in a distribution pursuant to a registration statement
filed by the Company under the Act or pursuant to a sale under Rule 144 under
the Act shall not be considered a Holder;

     (f) "1934 Act" shall mean the Securities Exchange Act of 1934, as amended,
or any similar federal statute enacted hereafter, and the rules and regulations
of the Commission thereunder, all as the same shall be in effect from time to
time; and

     (g) All other capitalized terms used herein but not otherwise defined shall
have the meanings ascribed to them in the Purchase Agreement.

     2.  Demand Registration.
         -------------------

     (a) If the Company shall receive a written request at any time after six
months following the initial public offering of Common Stock of the Company
(specifying that it is being made pursuant to this Section 2) from the Holders
of at least fifty percent (50%) of the Registrable Securities that the Company
file  an underwritten registration statement under the Act covering the
registration for offer and sale of at least twenty percent (20%) of the
Registrable Securities, then the Company shall promptly notify in writing all
other Holders of such request.  Within twenty calendar days after such notice
has been sent by the Company, any other Holder may give written notice to the
Company of its intent to include its Registrable Securities in the registration,
which notice shall specify the number of shares to be included.  As soon as
practicable after the expiration of such twenty-day period, the Company shall
use its reasonable best efforts to cause all Registrable Securities that Holders
have requested be registered to be registered under the Act (hereinafter a
"Demand Registration").  The Holders may, if they so desire, individually or
collectively condition their request or participation on price or other market
terms being available at the time of registration.

     (b) Notwithstanding the foregoing, the Company shall not be obligated to
effect, or to take any action to effect, any registration:

                                       2


     (1) Within ninety days after the effective date of any registration
statement effected by the Company, whether for its own account or for the
account of others; or

     (2) On Form S-1 (or any comparable or successor form to such form) after
the Company has effected two Demand Registrations and each such registration has
been declared or ordered effective.

     3.  Piggyback Registration.  Subject to the provisions of Section 9 of this
         ----------------------
Agreement, if at any time the Company proposes to register any of its securities
under the Act, either for its own account or for the account of others who are
not Holders, in connection with the public offering of such securities solely
for cash, on a registration form that would also permit the registration of
Registrable Securities, the Company shall, each such time, promptly give each
Holder written notice of such proposal.  Upon the written request of any Holder
given within twenty days after mailing of any such notice by the Company, the
Company shall use its reasonable best efforts to cause to be included in such
registration under the Act all the Registrable Securities that each such Holder
has requested be registered.  The Company shall not be obligated to complete
more than three piggyback registrations pursuant to this Section 3.

     4.  Registration on Form S-3.
         ------------------------

     (a) If (i) a Holder or Holders request in writing (specifying that such
request is being made pursuant to this Section 4) that the Company file under
the Act a registration statement on Form S-3 (or any successor registration form
to Form S-3 regardless of its designation) for a public offering of Registrable
Securities, and (ii) the Company is a registrant entitled to use Form S-3 (or
any successor registration form to Form S-3) to register such shares, then the
Company shall use its reasonable best efforts to cause such shares to be
registered on Form S-3 (or any successor registration form to Form S-3).

     (b) The Holders' rights to registration under this Section 4 are in
addition to, and not in lieu of, their rights to registration under Sections 2
and 3 of this Agreement.  Registrations on Form S-3 need not be underwritten.

     5.  Obligations of the Company.  Whenever required under this Agreement to
         --------------------------
use its reasonable best efforts to effect the registration of any Registrable
Securities, the Company shall, as expeditiously as reasonably possible:

     (a) Prepare and file with the Commission a registration statement covering
such Registrable Securities and

                                       3


use its reasonable best efforts to cause such registration statement to be
declared effective by the Commission as expeditiously as possible and to keep
such registration effective until the earlier of (i) the date when all
Registrable Securities covered by the registration statement have been sold or
(ii) 180 days from the effective date of the registration statement; provided,
that before filing a registration statement or prospectus or any amendments or
supplements thereto, the Company will furnish to each Holder of Registrable
Securities covered by such registration statement and the underwriters, if any,
copies of all such documents proposed to be filed (excluding exhibits, unless
any such person shall specifically request exhibits), which documents will be
subject to the review of such Holders and underwriters, and the Company will not
file such registration statement or any amendment thereto or any prospectus or
any supplement thereto (including any documents incorporated by reference
therein) with the Commission if (y) the Holders of a majority of the Registrable
Securities covered by such registration statement or the underwriters, if any,
shall reasonably object to such filing or (z) information in such registration
statement or prospectus concerning a particular selling Holder has changed and
such Holder or the underwriters, if any, shall reasonably object.

     (b) Prepare and file with the Commission such amendments and post-effective
amendments to such registration statement as may be necessary to keep such
registration statement effective during the period referred to in Section 5(a)
of this Agreement and to comply with the provisions of the Act with respect to
the disposition of all securities covered by such registration statement, and
cause the prospectus to be supplemented by any required prospectus supplement,
and as so supplemented to be filed with the Commission pursuant to Rule 424
under the Act.

     (c) Furnish to the selling Holders such numbers of copies of such
registration statement, each amendment thereto, the prospectus included in such
registration statement (including each preliminary prospectus), each supplement
thereto and such other documents as they may reasonably request in order to
facilitate the disposition of Registrable Securities owned by them.

     (d) Use its reasonable best efforts to register and qualify the Registrable
Securities under such other securities laws of such jurisdictions as shall be
reasonably requested by any selling Holder and do any and all other acts and
things which may be reasonably necessary or advisable to enable such selling
Holder to consummate the disposition of the Registrable Securities owned by such
Holder in such jurisdictions; provided

                                       4


that the Company shall not be required in connection therewith or as a condition
thereto to qualify to transact business or to file a general consent to service
of process in any such states or jurisdictions; and provided further that
(anything in this Agreement to the contrary notwithstanding with respect to the
bearing of expenses) if any jurisdiction in which the Registrable Securities
shall be qualified shall require that expenses incurred in connection with the
qualification of the Registrable Securities in that jurisdiction be borne by
selling shareholders, then such expenses shall be payable by the selling Holders
pro rata, to the extent required by such jurisdiction.

     (e) Promptly notify each selling Holder of such Registrable Securities at
any time when a prospectus relating thereto is required to be delivered under
the Act of the happening of any event as a result of which the prospectus
included in such registration statement contains an untrue statement of a
material fact or omits any fact necessary to make the statements therein not
misleading and, at the request of any such Holder, the Company will prepare a
supplement or amendment to such prospectus so that, as thereafter delivered to
the purchasers of such Registrable Securities, such prospectus will not contain
an untrue statement of a material fact or omit to state any fact necessary to
make the statements therein not misleading.

     (f) Provide a transfer agent and registrar for all such Registrable
Securities not later than the effective date of such registration statement.

     (g) Enter into such customary agreements (including underwriting agreements
in customary form for a primary offering) and take all such other actions as the
Holders of a majority of the Registrable Securities being sold or the
underwriters, if any, reasonably request in order to expedite or facilitate the
disposition of such Registrable Securities (including, without limitation,
effecting a stock split or a combination of shares).

     (h) Make available for inspection by any selling Holder of Registrable
Securities, any underwriter participating in any disposition pursuant to such
registration statement and any attorney, accountant or other agent retained by
any such selling Holder or underwriter, all financial and other records,
pertinent corporate documents and properties of the Company, and cause the
officers, directors, employees and independent accountants of the Company to
supply all information reasonably requested by any such seller, underwriter,
attorney, accountant or agent in connection with such registration statement
pursuant to agreements of confidentiality if reasonably requested.

                                       5


     (i) Promptly notify the Holders of Registrable Securities and the
underwriters, if any, of the following events and (if requested by any such
person) confirm such notification in writing:  (1) the filing of the prospectus
or any prospectus supplement and the registration statement and any amendment or
post-effective amendment thereto and, with respect to the registration statement
or any post-effective amendment thereto, the declaration of the effectiveness of
such documents, (2) any requests by the Commission for amendments or supplements
to the registration statement or the prospectus or for additional information,
(3) the issuance or threat of issuance by the Commission of any stop order
suspending the effectiveness of the registration statement or the initiation of
any proceedings for that purpose and (4) the receipt by the Company of any
notification with respect to the suspension of the qualification of the
Registrable Securities for sale in any jurisdiction or the initiation or threat
of initiation of any proceeding for such purpose.

     (j) Make every reasonable effort to prevent the entry of any order
suspending the effectiveness of the registration statement and obtain at the
earliest possible moment the withdrawal of any such order, if entered.

     (k) If reasonably requested by any underwriter or a selling Holder of
Registrable Securities in connection with any underwritten offering, promptly
incorporate in a prospectus supplement or post-effective amendment such
information as the underwriters and the Holders of a majority of the Registrable
Securities being sold agree should be included therein relating to the sale of
the Registrable Securities, including, without limitation, information with
respect to the number of Registrable Securities being sold to such underwriters,
the purchase price being paid therefor by such underwriters and any other terms
of the underwritten (or best efforts underwritten) offering of the Registrable
Securities to be sold in such offering, and make all required filings of such
prospectus supplement or post-effective amendment promptly after being notified
of the matters to be incorporated in such prospectus supplement or post-
effective amendment.

     (l) Prior to the filing of any document which is to be incorporated by
reference into the registration statement or the prospectus (after the initial
filing of the registration statement with the Commission), (i) promptly provide
copies of such document to counsel for the selling Holders of the Registrable
Securities and counsel for the underwriters, if any, (ii) make representatives
of the Company available for discussion of such document and (iii) make such
changes in such document

                                       6


prior to the filing thereof as counsel for such Holders or underwriters may
reasonably request.

     (m) Cooperate with the selling Holders of Registrable Securities and the
underwriters, if any, to facilitate the timely preparation and delivery of
certificates representing Registrable Securities to be sold and not bearing any
restrictive legends, and enable such Registrable Securities to be in such lots
and registered in such names as the underwriters may request at least two
business days prior to any delivery of Registrable Securities to the
underwriters.

     (n) Provide a CUSIP number for all Registrable Securities not later than
the effective date of the registration statement.

     (o) Prior to the effectiveness of the registration statement and any post-
effective amendment thereto and at each closing of an underwritten offering, (i)
make such representations and warranties to the selling Holders of such
Registrable Securities and the underwriters, if any, with respect to the
Registrable Securities and the registration statement as are customarily made by
issuers to underwriters in primary underwritten offerings; (ii) obtain opinions
of counsel to the Company and updates thereof (which counsel and which opinions
shall be reasonably satisfactory to the underwriters, if any, and to the Holders
of a majority of the Registrable Securities being sold) addressed to each
selling Holder and the underwriters, if any, covering the matters customarily
covered in opinions requested in underwritten offerings and such other matters
as may be reasonably requested by such Holders and underwriters or their
counsel; (iii) obtain "cold comfort" letters and updates thereof from the
Company's independent certified public accountants addressed to the selling
Holders of Registrable Securities and the underwriters, if any, such letters to
be in customary form and covering matters of the type customarily covered in
"cold comfort" letters by underwriters in connection with primary underwritten
offerings; and (iv) deliver such documents and certificates as may be reasonably
requested by the Holders of a majority of the Registrable Securities being sold
and by the underwriters, if any, to evidence compliance with clause (i) above
and with any customary conditions contained in the underwriting agreement or
other agreement entered into by the Company.

     (p) Otherwise use its best efforts to comply with all applicable rules and
regulations of the Commission, and make generally available to its security
holders earnings statements satisfying the provisions of Section 11(a) of the
Act, no later than 45 days after the end of any 12-month period (or 90 days, if

                                       7


such period is a fiscal year) (i) commencing at the end of any fiscal quarter in
which Registrable Securities are sold to underwriters in a firm or best efforts
underwritten offering, or (ii) if not sold to underwriters in such an offering,
beginning with the first month of the first fiscal quarter of the Company
commencing after the effective date of the registration statement, which
statements shall cover such 12-month periods.

     6.  Furnish Information.  It shall be a condition precedent to the
         -------------------
obligations of the Company (i) to take any action pursuant to this Agreement
that the Holders shall furnish to the Company such information regarding them,
the Registrable Securities held by them, and the intended method of disposition
of such Registrable Securities as the Company shall reasonably request and as
shall be required in connection with the action to be taken by the Company and
(ii) to cause any registration pursuant to this Agreement to become effective
for the Holders to have exercised their rights of conversion with respect to any
Registrable Securities proposed to be registered.

     7.  Suspension of Disposition of Registrable Securities.  Each selling
         ---------------------------------------------------
Holder of Registrable Securities agrees by acquisition of such Registrable
Securities that, upon receipt of any notice from the Company of the happening of
any event of the kind described in Section 5(e) of this Agreement, such Holder
will forthwith discontinue disposition of Registrable Securities until such
Holder's receipt of copies of the supplemented or amended prospectus
contemplated by Section 5(e) of this Agreement, or until it is advised in
writing (the "Advice") by the Company that the use of the prospectus may be
resumed, and has received copies of any additional or supplemental filings which
are incorporated by reference in the prospectus, and, if so directed by the
Company, such Holder will deliver to the Company (at the expense of the Company)
all copies, other than permanent file copies then in such Holder's possession,
of the prospectus covering such Registrable Securities current at the time of
receipt of such notice.  In the event the Company shall give any such notice,
the time periods mentioned in Section 5(a) of this Agreement shall be extended
by the number of days during the period from and including the date of the
giving of such notice pursuant to Section 5(e) of this Agreement to and
including the date when each selling Holder of Registrable Securities shall have
received the copies of the supplemented or amended prospectus contemplated by
Section 5(e) of this Agreement or the Advice.

     8.  Expenses of Registration.  All reasonable expenses incurred in
         ------------------------
connection with a registration pursuant to Sections 2, 3 and 4 of this Agreement
(excluding underwriters' discounts and commissions) including, without
limitation, all registration

                                       8


and qualification fees, printing and accounting fees, fees and disbursements of
counsel for the Company shall be borne by the Company; provided, however, that
the Company shall not be required to pay for any expenses of any registration
proceeding begun pursuant to Section 2 of this Agreement if the registration
request is subsequently withdrawn at the request of the Holders, unless (i) the
Holders agree to forfeit their right to a demand registration pursuant to
Section 2 of this Agreement; or (ii) there has been a material adverse change in
the business or prospects of the Company after the date of any demand for
registration made pursuant to Section 2 of this Agreement, which change has
caused such request to be withdrawn by the Holders, in which case the Holders
shall not be required to pay any of the expenses for such registration and shall
retain the right to require the Company to register Registrable Securities
pursuant to Section 2 of this Agreement.

     9.  Underwriting Requirements; Priorities.
         -------------------------------------

     (a) The Holders of a majority of the Registrable Securities included in any
registration under Section 2 or 4 of this Agreement will have the right to
select the investment banker(s) and manager(s) to administer the offering, if
any, subject to the approval of the Company, which will not be unreasonably
withheld.  The Company will not include in any registration under Section 2 or 4
of this Agreement any securities that are not Registrable Securities without the
written consent of the Holders of a majority of the Registrable Securities
requesting such registration.  If other securities are permitted to be included
in a registration under Section 2 or 4 of this Agreement which is an
underwritten offering and the managing underwriters advise the Company in
writing that in their opinion the number of Registrable Securities and other
securities requested to be included exceeds the number of Registrable Securities
and other securities that can be sold at the desired price in such offering, the
Company will include in such registration (i) first, prior to the inclusion of
any securities that are not Registrable Securities, the number of Registrable
Securities requested to be included which in the opinion of such underwriters
can be sold, pro rata among the respective Holders on the basis of the amount of
Registrable Securities owned and (ii) second, all other securities permitted to
be included in such registration.

     (b) The Company will have the right to select the investment banker(s) and
manager(s) to administer any offering to which Section 3 of this Agreement is
applicable, subject to the approval of the Holders of a majority of the
Registrable Securities included in such registration, which approval will not be
unreasonably withheld.  If a registration under Section 3 of

                                       9


this Agreement is an underwritten primary registration on behalf of the Company,
and the managing underwriters advise the Company in writing that in their
opinion the number of securities requested to be included in such registration
exceeds the number which can be sold at the desired price in such offering, the
Company will include in such registration (i) first, the securities the Company
proposes to sell, (ii) second, the Registrable Securities requested to be
included in such registration by the Holders pro rata among the Holders thereof
on the basis of the amount of Registrable Securities owned and (iii) third, all
other securities requested to be included in such registration. If a
registration under Section 3 of this Agreement is an underwritten secondary
registration on behalf of holders of securities of the Company (or a combined
primary offering by the Company and secondary offering by the Company's
stockholders) and the managing underwriters advise the Company in writing that
in their opinion the number of securities requested to be included in such
registration exceeds the number that can be sold at the desired price in such
offering, the Company will include in such registration (i) first, the
securities requested to be included therein by the Holders requesting such
registration but not in excess of one-third of the total number of shares to be
included in such registration and by other holders of Company securities with
contractual registration rights, pro rata among the holders of such securities
on the basis of the number of shares requested to be included therein, (ii)
second, securities to be sold for the account of the Company, and (iii) third,
other securities requested to be included in such registration.

     (c) No person may participate in any underwritten registration hereunder
unless such person (i) agrees to sell such person's securities on the basis
provided in any underwriting arrangements approved by the persons entitled
hereunder to approve such arrangements and (ii) completes and executes all
questionnaires, powers of attorney, indemnities, underwriting agreements and
other documents required under the terms of such underwriting arrangements.

     10.  Termination of the Company's Obligations.
          ----------------------------------------

     (a) The Company shall have no further obligations pursuant to Section 2 of
this Agreement with respect to any request or requests made by any Holder after
the Company has, at the demand of the Holders pursuant to Section 2 of this
Agreement, effected two registrations in which registration statements have
remained effective for at least 180 days or have become effective and all
Registrable Securities covered thereby have been sold pursuant thereto.

                                       10


     (b) The Company shall have no further obligations pursuant to this
Agreement if the Company sells all or substantially all its assets.

     11.  Reports Under the 1934 Act.  With a view to making available to the
          --------------------------
Holders the benefits of Rule 144 promulgated under the Act and any other rule or
regulation of the Commission that may at any time permit a Holder to sell
securities of the Company to the public without registration, the Company agrees
to use its reasonable best efforts to:

     (a) Make and keep public information available, as those terms are
understood and defined in Rule 144, at all times subsequent to ninety days after
the effective date of the first registration statement covering an underwritten
public offering filed under the Act by the Company;

     (b) File with the Commission in a timely manner all reports and other
documents required of the Company under the Act and the 1934 Act at any time
after it is subject to such registration requirements; and

     (c) Furnish to any Holder so long as such Holder owns any of the
Registrable Securities forthwith upon request a written statement by the Company
that it has complied with the reporting requirements of Rule 144 (at any time
after ninety days after the effective date of said first registration statement
filed by the Company), and of the Act and the 1934 Act (at any time after it has
become subject to such reporting requirements), a copy of the most recent annual
or quarterly report of the Company, and such other reports and documents so
filed by the Company as may be reasonably requested by any Holder in availing
any Holder of any rule or regulation of the Commission permitting the selling of
any such securities without registration.

     12.  Lockup Agreement.
          ----------------

     (a) The Holders agree in connection with any registration of the Company's
securities upon the request of the underwriters managing any underwritten
offering of the Company' securities, not to sell, make any short sale of,
pledge, grant any option for the purchase of or otherwise dispose of any
Registrable Securities (other than those included in the registration) without
the prior written consent of the Company or such underwriters, as the case may
be, during the seven days prior to and during the 180-day period beginning on
the effective date of such registration as the Company or the underwriters may
specify; provided that all officers, directors and holders of more than five
percent (5%) on a fully-diluted basis of the outstanding capital stock of the
Company similarly agree.

                                       11


     (b) The Company agrees (i) not to effect any public sale or distribution of
its equity securities, or any securities convertible into or exchangeable or
exercisable for such securities, during the seven days prior to and during the
180-day period beginning on the effective date of any registration statement
related to an underwritten offering pursuant to which Registrable Securities are
to be sold (except as part of such underwritten registration or pursuant to
registrations on Form S-8 or any successor form), unless the underwriters
managing the registered public offering otherwise agree, and (ii) to use best
efforts to cause each holder of at least five percent (5%) (on a fully diluted
basis) of its equity securities, or any securities convertible into or
exchangeable or exercisable for such securities, purchased from the Company at
any time after the date of this Agreement (other than in a registered public
offering) to agree not to effect any sale or distribution of any such securities
during such period (except as part of such underwritten registration, if
otherwise permitted), unless the underwriters managing the registered public
offering otherwise agree.

     (c) Notwithstanding the provisions of Section 12(a) of this Agreement, and
unless otherwise objected to by the underwriters, the Holders may, on or after
the thirtieth day following the effective date of a registration statement
referred to in such Section, sell in the aggregate an amount of Registrable
Securities (in addition to those included in the registration) not exceeding the
lesser of 5% of the number of shares registered or 2.5% of the Company's
outstanding Common Stock (calculated on a fully diluted basis) (collectively,
the "De Minimis Securities").  In the absence of an agreement among the Holders
to the contrary, each Holder may sell its pro rata share of the De Minimis
Securities, determined by reference to the proportion that the amount of
Registrable Securities it owns prior to such registration bears to the total of
Registrable Securities outstanding at such time.

     13.  Certain Limitations in Connection with Future Grants of Registration
          --------------------------------------------------------------------
Rights.  From and after the date of this Agreement, the Company shall not enter
- ------
into any agreement with any holder or prospective holder of any securities of
the Company providing for the granting to such holder of registration rights
without the written consent of the Holders of a majority of the then outstanding
Registrable Securities.

     14.  Transfer of Registration Rights.  Provided that the Company is given
          -------------------------------
written notice by the Holder at the time of such transfer stating the name and
address of the transferee and identifying the securities with respect to which
the rights under

                                       12


this Agreement are being assigned, the registration rights under this Agreement
may be transferred in whole or in part at any time.

     15.  Indemnification.  In the event any Registrable Securities are included
          ---------------
in a registration statement under this Agreement:

     (a) To the full extent permitted by law, the Company will, and hereby does
indemnify and hold harmless each Holder requesting or joining in a registration,
each director, officer, partner, employee, or agent for such Holder, any
underwriter (as defined in the Act) for such Holder, and each person, if any,
who controls such Holder or underwriter within the meaning of the Act, against
any losses, claims, damages or liabilities, joint or several, to which they may
become subject under the Act and applicable state securities laws insofar as
such losses, claims, damages or liabilities (or actions in respect thereof)
arise out of or are based on any untrue or alleged untrue statement of any
material fact contained in such registration statement, including any
preliminary prospectus or final prospectus contained therein or any amendments
or supplements 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
in light of the circumstances under which they were made or necessary to make
the statements therein not misleading or arise out of any violation by the
Company of any rule or regulation promulgated under the Act applicable to the
Company and relating to action or inaction required of the Company in connection
with any such registration; and will reimburse each such person or entity for
any legal or other expenses reasonably incurred by them in connection with
investigating or defending any such loss, claim, damage, liability, or action;
provided, however, that the indemnity agreement contained in this Section 15(a)
shall not apply to amounts paid in settlement of any such loss, claim, damage,
liability, or action if such settlement is effected without the consent of the
Company (which consent shall not be unreasonably withheld) nor shall the Company
be liable in any such case for any such loss, claim, damage, liability or action
to the extent that it arises out of or is based upon an untrue statement or
alleged untrue statement or omission or alleged omission made in connection with
such registration statement, preliminary prospectus, final prospectus, or
amendments or supplements thereto, in reliance upon and in conformity with
written information furnished expressly  for use in connection with such
registration by or on behalf of any such Holder, underwriter or controlling
person.

     (b) To the full extent permitted by law, each Holder requesting or joining
in a registration under this Agreement will

                                       13


indemnify and hold harmless the Company, each of its directors, each of its
officers who have signed the registration statement, each person, if any, who
controls the Company within the meaning of the Act, and any underwriter for the
Company (within the meaning of the Act), each other selling Holder and each
person, if any, who controls such other selling Holder within the meaning of
Section 15 of the Act against any losses, claims, damages or liabilities, joint
or several, to which the Company or any such director, officer, controlling
person or underwriter may become subject, under the Act and applicable state
securities laws, insofar as such losses, claims, damages or liabilities (or
actions in respect thereof) arise out of or are based upon any untrue statement
or alleged untrue statement of any material fact contained in such registration
statement, including any preliminary prospectus or final prospectus contained
therein or any amendments or supplements 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 light of the circumstances, 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 such registration statement, preliminary or final
prospectus, or amendments or supplements thereto, in reliance upon and in
conformity with written information furnished by such Holder expressly for use
in connection with such registration; and each such Holder will reimburse any
legal or other expenses reasonably incurred by the Company or any such director,
officer, controlling person or underwriter in connection with investigating or
defending any such loss, claim, damage, liability or action; provided, however,
that the indemnity agreement contained in this Section 15(b) shall not apply to
amounts paid in settlement of any such loss, claim, damage, liability or action
if such settlement is effected without the consent of such Holder (which consent
shall not be unreasonably withheld).

     In no event shall the liability of any selling Holder of Registrable
Securities hereunder be greater than the dollar amount of the proceeds received
by such Holder upon the sale of the Registrable Securities giving rise to such
indemnification obligation.

     (c) Promptly after receipt by an indemnified party under this Section 15 of
notice of the commencement of any action or knowledge of a claim that would, if
asserted, give rise to a claim for indemnity hereunder, such indemnified party
will, if a claim in respect thereof is to be made against any indemnifying party
under this Section 15, notify the indemnifying party in writing of the
commencement thereof or knowledge thereof and the indemnifying party shall have
the right to participate in, and,

                                       14


to the extent the indemnifying party so desires, jointly with any other
indemnifying party similarly noticed, to assume the defense thereof with counsel
mutually satisfactory to the parties. The failure to notify an indemnifying
party promptly of the commencement of any such action or of the knowledge of any
such claim, if prejudicial to his ability to defend such action, shall relieve
such indemnifying party of any liability to the indemnified party under this
Section 15, but the omission so to notify the indemnifying party will not
relieve him of any liability that he may have to any indemnified party otherwise
than under this Section 15.

     16.  Remedies.  In addition to being entitled to exercise all rights
          --------
provided in this Agreement and other agreements entered into by and among the
Company and one or more of the Holders as well as all rights granted by law,
including recovery of damages, each Holder of Registrable Securities shall be
entitled to specific performance of its rights under this Agreement.  The
Company agrees that monetary damages would not be adequate compensation for any
loss incurred by reason of a breach by it of the provisions of this Agreement
and hereby agrees not to raise the defense in any action for specific
performance that a remedy at law would be adequate.

     17.  Amendments and Waivers. Any term of this Agreement may be amended and
          ----------------------
the observance of any term of this Agreement may be waived either generally or
in a particular instance and either retroactively or prospectively with the
written consent of the Holders of a majority of the then outstanding Registrable
Securities.  Any such amendment or waiver effected in accordance with this
Section 17 shall be binding on each Holder.

     18.  Notices.  All notices and other communications provided for or
          -------
permitted hereunder shall be made in writing by hand-delivery, certified first-
class mail, telex, telecopier, or air courier guaranteeing overnight delivery:

     (a) If to a Holder of Registrable Securities, at the most current address
given by such Holder to the Company in accordance with the provisions of this
Section 18, which address initially is, with respect to the Investors, the
address set forth in the Purchase Agreement, with a copy (which shall not
constitute notice) to their respective counsel as identified therein; and

     (b) If to the Company, initially at its address set forth in the Purchase
Agreement and thereafter at such other address, notice of which is given in
accordance with the provisions of this Section 18.

                                       15


     All such notices and communications shall be deemed to have been duly
given:  at the time delivered by hand, if personally delivered; five business
days after being deposited in the mail, postage prepaid, if mailed; when
answered back, if telexed; when receipt acknowledged, if telecopied; and on the
next business day, if timely delivered to an air courier guaranteeing overnight
delivery.

     19.  Counterparts.  This Agreement may be executed in any number of
          ------------
counterparts and by the parties hereto in separate counterparts, each of which
when so executed shall be deemed to be an original and all of which taken
together shall constitute one and the same agreement.

     20.  Headings.  The headings in this Agreement are for convenience of
          --------
reference only and shall not limit or otherwise affect the meaning hereof.

     21.  Governing Law.  This Agreement shall be governed by and construed in
          -------------
accordance with the laws of the State of Delaware.

     22.  Severability.  In the event that any one or more of the provisions
          ------------
contained herein, or the application thereof in any circumstance, is held
invalid, illegal or unenforceable, the validity, legality and enforceability of
any such provision in every other respect and of the remaining provisions
contained herein shall not be affected or impaired thereby.

     23.  Entire Agreement.  This Agreement is intended by the parties as a
          ----------------
final expression of their agreement and intended to be a complete and exclusive
statement of the agreement and understanding of the parties hereto in respect of
the subject matter contained herein.  There are no restrictions, promises,
warranties or undertakings, other than those set forth or referred to herein
with respect to the registration rights granted by the Company with respect to
the Company Shares.  This Agreement supersedes all prior agreements and
understandings between the parties with respect to such subject matter.

                                       16


     24.  Parties Benefited.  Nothing in this Agreement, express or implied, is
          -----------------
intended to confer upon any third party any rights, remedies, obligations or
liabilities.

                                       17


     IN WITNESS WHEREOF, the parties have executed this Registration Rights
Agreement as of the date first above written.


MAXYGEN, INC.
4001 Miranda Avenue
Palo Alto, CA 94304


/s/ Isaac Stein
- ---------------
Signature


Isaac Stein
- -----------
Name (please print)



Chief Financial Officer
- -----------------------
Title


                                   INVESTORS
                                   ---------

AFFYMAX TECHNOLOGIES N.V.                       With copy to:
Glaxo Wellcome House                            Glaxo Wellcome House
Berkeley Avenue                                 Berkeley Avenue
Greenford, Middlesex,                           Greenford, Middlesex,
United Kingdom UB6 0NN                          United Kingdom UB6 0NN
Attn: Adrian Hennah                             Attn:  H. Khan
     --------------                                    ---------
Fax:  44-181-966-3368                           Fax:  44-181-966-2303
      ---------------                                 ---------------



/s/ Adrian Hennah
- -----------------
Signature



Adrian Hennah
- -------------
Name (please print)



Director
- --------
Title



                               SIGNATURE PAGE TO
                    REGISTRATION RIGHTS AGREEMENT CONTINUED


GLAXO GROUP LIMITED          With copy to:
Glaxo Wellcome House         Glaxo Wellcome House
Berkeley Avenue              Berkeley Avenue
Greenford, Middlesex,         Greenford, Middlesex,
United Kingdom UB6 0NN        United Kingdom UB6 0NN
Attn:Stephen J. Cowden        Attn:  H. Khan
     -----------------               -------
Fax:  44-171-408-8679        Fax:  44-181-966-2303
      ---------------              ---------------



/s/  Stephen J. Cowden
- ----------------------
Signature



Stephen J. Cowden
- -----------------
Name (please print)




Company Secretary
- -----------------
Title




/s/ Alejandro Zaffaroni
- -----------------------
Dr. Alejandro Zaffaroni
c/o Maxygen, Inc.
4001 Miranda Avenue
Palo Alto, CA 94304