AFFYMETRIX INC
8-K, 1998-03-24
COMMERCIAL PHYSICAL & BIOLOGICAL RESEARCH
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                      SECURITIES AND EXCHANGE COMMISSION

                            WASHINGTON, D.C. 20549

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

                                   FORM 8-K

                                CURRENT REPORT

                    PURSUANT TO SECTION 13 OR 15(d) OF THE
                       SECURITIES EXCHANGE ACT OF 1934

DATE OF REPORT (DATE OF EARLIEST EVENT REPORTED)   MARCH 9, 1998
                                                 ------------------------------
                                AFFYMETRIX, INC.
- -------------------------------------------------------------------------------
             (EXACT NAME OF REGISTRATION AS SPECIFIED IN CHARTER)


         CALIFORNIA                     333-38167              77-0319159
- -------------------------------------------------------------------------------
(STATE OR OTHER JURISDICTION           (COMMISSION            (IRS EMPLOYER 
     OF INCORPORATION                  FILE NUMBER)         IDENTIFICATION NO.)

3380 CENTRAL EXPRESSWAY, SANTA CLARA CA                                   95051
- -------------------------------------------------------------------------------
(ADDRESS OF PRINCIPAL EXECUTIVE OFFICES)                             (ZIP CODE)

REGISTRANT'S TELEPHONE NUMBER, INCLUDING AREA CODE   (408) 731-5000


- -------------------------------------------------------------------------------
        (FORMER NAME OR FORMER ADDRESS, IF CHANGED SINCE LAST REPORT)


<PAGE>

ITEM 5.   OTHER EVENTS

          On March 9, 1998, the Company entered into a definitive agreement 
to sell 1,634,522 shares of Series AA Preferred Stock to Glaxo Wellcome 
Americas, Inc. for approximately $50 million.  The text of the Company's 
press release filed pursuant to Section 135(c) is attached hereto as Exhibit 
99.1.

ITEM 7.   EXHIBITS

(c)  EXHIBITS:

     Exhibit
     Number
     -------

     4     Certificate of Determination as filed with the Secretary of State of
           the State of California on March 11, 1998.

     10    Series AA Preferred Stock Purchase Agreement dated March 9, 1998 by 
           and between Affymetrix, Inc. and Glaxo Wellcome Americas, Inc. with 
           exhibits.

     99    March 10, 1998 Press Release: "Affymetrix Announces Definitive
           Agreement to Sell $50 Million of Series AA Preferred Stock."

ITEM 9.   SALES OF EQUITY SECURITIES PURSUANT TO REGULATION S.

          None of the securities in the above referenced transaction were 
sold in reliance upon Regulation S of the Securities Act of 1933, as amended.

                                       2

<PAGE>

                                   SIGNATURES

          Pursuant to the requirements of the Securities Exchange Act of 
1934, the Registrant has duly caused this report to be signed on its behalf 
by the undersigned hereunto duly authorized.

                                    Affymetrix, Inc.
                                   --------------------------------------
                                    (Registrant)

Date:  March 17, 1998               By:  /s/ Edward M. Hurwitz
                                   --------------------------------------
                                     Edward M. Hurwitz
                                     Vice President and Chief Financial Officer
                                     (Duly Authorized Officer and
                                     Principal Financial Officer)

                                       3

<PAGE>

                                AFFYMETRIX, INC.

                                 EXHIBIT INDEX

Exhibit
Number
- -------

4       Certificate of Determination as filed with the Secretary of State of 
        the State of California on March 11, 1998.

10      Series AA Preferred Stock Purchase Agreement dated March 9, 1998 by 
        and between Affymetrix, Inc. and Glaxo Wellcome Americas, Inc. 
        with exhibits.

99      March 10, 1998 Press Release: "Affymetrix Announces Definitive 
        Agreement  to Sell $50 Million of Series AA Preferred Stock."

                                       4


<PAGE>

                         CERTIFICATE OF DETERMINATION
                         OF SERIES AA PREFERRED STOCK
                             OF AFFYMETRIX, INC.,
                           A CALIFORNIA CORPORATION
        (PURSUANT TO SECTION 401 OF THE CALIFORNIA CORPORATIONS CODE)


The undersigned Stephen P.A. Fodor and Edward M. Hurwitz, do hereby certify:

1.  That they are the duly elected and acting President and Chief Executive
    Officer and the Chief Financial Officer, respectively, of Affymetrix, Inc.,
    a California corporation (the "Corporation").

2.  The authorized number of shares of the Corporation's Preferred Stock is
    27,500,000, and the number of shares constituting Series AA Preferred Stock
    is 1,634,522, none of the shares of that series has been issued.

3.  That pursuant to the authority conferred upon the Board of Directors by the
    Amended and Restated Articles of Incorporation of the Corporation, the Board
    of Directors adopted the following resolution:

              RESOLVED, that pursuant to the authority granted to and
         vested in the Board of Directors of the Corporation in
         accordance with the provisions of the Corporation's Amended
         and Restated Articles of Incorporation, the Board of Directors
         hereby creates a new series of Preferred Stock designated as
         Series AA Preferred Stock which shall be subject to the
         following rights, preferences, privileges and restrictions
         thereof as follows:

RIGHTS, PREFERENCES, PRIVILEGES AND RESTRICTIONS OF PREFERRED STOCK. The 
rights, preferences, privileges, and restrictions granted to and imposed on 
the Series AA Preferred Stock, which series shall consist of one million six 
hundred thirty four thousand five hundred twenty two (1,634,522) shares (the 
"Series AA Preferred Stock"), are as set forth below in this Certificate of 
Determination.  

          1.   DIVIDEND PROVISIONS.

          (a)  Subject to the rights of any series of Preferred Stock that 
may from time to time come into existence, the holders of shares of Series AA 
Preferred Stock shall be entitled to receive dividends payable in cash, out 
of any assets legally available therefor, prior and in preference to any 
declaration or payment of any dividend (payable other than in Common Stock or 
other securities and rights convertible into or entitling the holder thereof 
to receive, directly or indirectly, additional shares of Common Stock of this 
Corporation) on the Common Stock of this Corporation, at the rate per share 
per annum of $1.99 (as adjusted for any stock splits, stock dividends, 
combinations, recapitalizations or the like with respect to the Series AA 
Preferred Stock) payable in two equal installments on June 30 and December 31 
of each year so long as such share of Series AA Preferred Stock is then 
outstanding.  Such dividends shall accrue on 

<PAGE>

each share from the Purchase Date (as defined below), and shall accrue from 
day to day, whether or not earned or declared.  Such dividends shall be 
cumulative so that, except as provided below, if such dividends in respect of 
any previous or current dividend period, at the annual rate specified above, 
shall not have been paid, the deficiency shall first be fully paid before any 
dividend or other distribution shall be paid on or declared and set apart for 
the Common Stock.  Cumulative dividends with respect to a share of Series AA 
Preferred Stock which are accrued, payable and/or in arrears shall, upon 
conversion of such share to Common Stock or redemption of such share, be paid 
to the extent assets are legally available therefor pursuant to the 
provisions of Section 2 and Section 3, respectively, and any amounts for 
which assets are not legally available shall be paid promptly as assets 
become legally available therefor; any partial payment will be made pro rata 
among the holders of such shares.  The holders of the outstanding Series AA 
Preferred Stock can waive any dividend preference that such holders shall be 
entitled to receive under this Section 1 upon the affirmative vote or written 
consent of the holders of at least a majority of the Series AA Preferred 
Stock then outstanding.

          (b)  Subject to the rights of any shares of Preferred Stock that 
may from time to time come into existence and in addition to the amounts paid 
pursuant to subsection 1(a) above, the holders of shares of Series AA 
Preferred Stock shall be entitled to receive an amount equal to any dividend 
paid (other than dividends paid in Common Stock or other securities and 
rights convertible into or entitling the holder thereof to receive, directly 
or indirectly, additional shares of Common Stock of this Corporation) on the 
Common Stock of this Corporation (as determined on a per annum basis and on 
as a converted basis for the Series AA Preferred Stock), payable when, as and 
if declared by the Board of Directors.  Such dividends shall not be 
cumulative.

          2.   LIQUIDATION PREFERENCE.

          (a)  In the event of any liquidation, dissolution or winding up of 
this Corporation, either voluntary or involuntary, subject to the rights of 
series of Preferred Stock that may from time to time come into existence, the 
holders of Series AA Preferred Stock shall be entitled to receive, prior and 
in preference to any distribution of any of the assets of this Corporation to 
the holders of Common Stock by reason of their ownership thereof, an amount 
per share equal to the sum of (i) $30.59 for each outstanding share of Series 
AA Preferred Stock (the "Original Series AA Issue Price") (subject to 
adjustment of such fixed dollar amounts for any stock splits, stock 
dividends, combinations, recapitalizations or the like with respect to the 
Series AA Preferred Stock), (ii) accrued but unpaid dividends on such share, 
and (iii) a per share amount equal to the difference obtained by subtracting 
(A) the product of ten percent of the annual per share dividend multiplied by 
a fraction, the numerator of which is the number of days elapsed since the 
date upon which the first share of Series AA Preferred Stock was first issued 
(the "Purchase Date") and the denominator of which is 365, from (B) the 
annual per share dividend.  The sum obtained by adding the amounts described 
in clauses (i), (ii) and (iii) of the preceding sentence is referred to 
herein as the "Series AA Liquidation Preference".  If upon the occurrence of 
such event, the assets and funds thus distributed among the holders of the 
Series AA Preferred Stock shall be insufficient to permit the payment to such 
holders of the full aforesaid preferential amounts, then, subject to the 
rights of series of Preferred Stock that may 

                                       2

<PAGE>

from time to time come into existence, the entire assets and funds of this 
Corporation legally available for distribution shall be distributed ratably 
among the holders of the Series AA Preferred Stock in proportion to the 
amount of such stock owned by each such holder.

          (b)  Upon the completion of the distribution required by 
subparagraph (a) of this Section 2 and any other distribution that may be 
required with respect to series of Preferred Stock that may from time to time 
come into existence, if assets remain in this Corporation, the holders of the 
Common Stock of this Corporation, shall receive an amount per share of Common 
Stock equal to the quotient obtained by dividing (i) the Series AA 
Liquidation Preference, by (ii) the number of shares of Common Stock into 
which one (1) share of Series AA Preferred Stock could then be converted 
pursuant to Section 4 hereof.  If upon the occurrence of such event, the 
assets and funds thus distributed among the holders of the Common Stock shall 
be insufficient to permit the payment to such holders of the full aforesaid 
preferential amount, then, subject to the rights of series of Preferred Stock 
that may from time to time come into existence, the entire remaining assets 
and funds of this Corporation legally available for distribution shall be 
distributed ratably among the holders of the Common Stock in proportion to 
the amount of such stock owned by each such holder.

          (c)  After the distributions described in subsection (a) and (b) 
above have been paid, subject to the rights of series of Preferred Stock that 
may from time to time come into existence, the remaining assets of this 
Corporation available for distribution to shareholders shall be distributed 
among the holders of Series AA Preferred Stock and Common Stock pro rata 
based on the number of shares of Common Stock held by each (assuming full 
conversion of all such Series AA Preferred Stock).

          (d)  (i)  The following events shall be deemed to be a liquidation, 
dissolution or winding up within the meaning of this Section 2: (A) a 
consolidation or merger of this Corporation with or into any other 
corporation or corporations as a result of which the holders of voting stock 
of this Corporation immediately prior to such transaction do not own, 
directly or indirectly, more than 50% of the voting power of the surviving 
corporation or its parent corporation immediately after such transaction, or 
(B) a sale, conveyance or disposition of all or substantially all of the 
assets of this Corporation.

               (ii) In any of such events, the value of the assets 
distributed to the shareholders of this Corporation shall be determined as 
set forth herein.  If the assets distributed to the shareholders of this 
Corporation consist of other than cash or securities, the value of such 
assets shall be the fair market value thereof, as determined by the this 
Corporation and the holders of at least a majority of the voting power of all 
the then outstanding shares of Preferred Stock. If the assets distributed to 
the shareholders of this Corporation consist of securities, such securities 
shall be valued as follows:

                    (A)  Securities not subject to investment letter or other 
similar restrictions on free marketability covered by (B) below:

                         (1)  If traded on a securities exchange or through 
the Nasdaq National Market, the value shall be deemed to be the average of 
the closing prices of the 

                                       3

<PAGE>

securities on such exchange or system over the twenty (20) trading day period 
ending three (3) trading days prior to the closing;

                         (2)  If actively traded over-the-counter, the value 
shall be deemed to be the average of the closing bid or sale prices 
(whichever is applicable) over the twenty (20) trading day period ending 
three (3) trading days prior to the closing; and

                         (3)  If there is no active public market, the value 
shall be the fair market value thereof, as mutually determined by this 
Corporation and the holders of at least a majority of the voting power of all 
then outstanding shares of Preferred Stock.

                    (B)  The method of valuation of securities subject to 
investment letter or other restrictions on free marketability (other than 
restrictions arising solely by virtue of a shareholder's status as an 
affiliate or former affiliate) shall be to make an appropriate discount from 
the market value determined as above in (A) (1), (2) or (3) to reflect the 
approximate fair market value thereof, as mutually determined by this 
Corporation and the holders of at least a majority of the voting power of all 
then outstanding shares of such Preferred Stock. 

          3.   REDEMPTION.

          (a)  REDEMPTION AT THE OPTION OF THIS CORPORATION.

               (i)  Subject to the rights of series of Preferred Stock that 
may from time to time come into existence, at any time on or prior to March 
9, 2001, this Corporation may at any time it may lawfully do so, at the 
option of the Board of Directors, redeem in whole or in part the Series AA 
Preferred Stock by paying in cash therefor a sum equal to (A) the Original 
Series AA Issue Price (subject to adjustment of such fixed dollar amount for 
any stock splits, stock dividends, combinations, recapitalizations or the 
like with respect to the Series AA Preferred Stock), plus (B) accrued but 
unpaid dividends on such share (the "Early Redemption Price"); provided that 
the closing sale price of this Corporation's Common Stock on the Nasdaq 
National Market (or such other national securities exchange on which the 
Common Stock is then listed) has been at or above $52.00 (subject to 
adjustment of such fixed dollar amount for any stock splits, stock dividends, 
combinations, recapitalizations or the like with respect to the Common Stock) 
for twenty (20) of thirty (30) consecutive trading days prior to the 
applicable Corporation Redemption Date (as defined below), which thirty (30) 
day period shall have ended not more than ten (10) trading days prior to the 
date of the Corporation Redemption Notice (as defined below).  Any redemption 
effected pursuant to this subsection 3(a)(i) shall be made on a pro rata 
basis among the holders of the Series AA Preferred Stock in proportion to the 
number of shares of Series AA Preferred Stock then held by them.

               (ii) Subject to the rights of series of Preferred Stock that 
may from time to time come into existence, at any time after March 9, 2001, 
this Corporation may at any time it may lawfully do so, at the option of the 
Board of Directors, redeem in whole or in part the Series AA Preferred Stock 
by paying in cash therefor a sum equal to the Series AA Liquidation 
Preference (the "Late Redemption Price").  Any redemption effected pursuant 
to this subsection 

                                       4

<PAGE>

3(a)(ii) shall be made on a pro rata basis among the holders of the Series AA 
Preferred Stock in proportion to the number of shares of Series AA Preferred 
Stock then held by them.

               (iii)     Subject to the rights of series of Preferred Stock 
that may from time to time come into existence, at least twenty (20) but no 
more than thirty (30) days prior to the date on which this Corporation 
proposes to redeem any shares of Series AA Preferred Stock (each a 
"Corporation Redemption Date"), written notice shall be personally delivered, 
sent by reliable international courier, or sent by confirmed facsimile to 
each holder of record (at the close of business on the business day next 
preceding the day on which notice is given) of the Series AA Preferred Stock 
to be redeemed, at the address last shown on the records of this Corporation 
for such holder, notifying such holder of the redemption to be effected on 
the applicable Corporation Redemption Date, specifying the number of shares 
to be redeemed from such holder, the applicable Corporation Redemption Date, 
the Early or Late Redemption Price, as applicable, the place at which payment 
may be obtained and calling upon such holder to surrender to this 
Corporation, in the manner and at the place designated, his, her or its 
certificate or certificates representing the shares to be redeemed (the 
"Corporation Redemption Notice").  Except as provided in subsection 3(a)(iv) 
or 3(a)(v), on or after each Corporation Redemption Date, each holder of 
Series AA Preferred Stock to be redeemed on such Corporation Redemption Date 
shall surrender to this Corporation the certificate or certificates 
representing such shares, in the manner and at the place designated in the 
Corporation Redemption Notice, and thereupon the Early or Late Redemption 
Price, as applicable, of such shares shall be payable to the order of the 
person whose name appears on such certificate or certificates as the owner 
thereof and each surrendered certificate shall be cancelled.  In the event 
less than all the shares represented by any such certificate are redeemed, a 
new certificate shall be issued representing the unredeemed shares.  Any 
shares of Series AA Preferred Stock that are not redeemed shall remain 
subject to redemption by this Corporation pursuant to this Section 3(a).

               (iv) Each holder of Series AA Preferred Stock may, at anytime 
up to two (2) trading days prior to the applicable Corporation Redemption 
Date, elect to convert all shares of Series AA Preferred Stock designated for 
redemption in the Corporation Redemption Notice into shares of Common Stock 
pursuant to Section 4 below.

               (v)  From and after each Corporation Redemption Date, unless 
there shall have been a default in payment of the Early or Late Redemption 
Price, as applicable, all rights of the holders of shares of Series AA 
Preferred Stock designated for redemption on such Corporation Redemption Date 
in the Corporation Redemption Notice as holders of Series AA Preferred Stock 
(except the right to receive the Early or Late Redemption Price, as 
applicable, without interest upon surrender of their certificate or 
certificates) shall cease with respect to such shares, and such shares shall 
not thereafter be transferred on the books of this Corporation or be deemed 
to be outstanding for any purpose whatsoever.  Subject to the rights of 
series of Preferred Stock that may from time to time come into existence, if 
the funds of this Corporation legally available for redemption of shares of 
Series AA Preferred Stock on any Corporation Redemption Date are insufficient 
to redeem the total number of shares of Series AA Preferred Stock to be 
redeemed on such date, those funds that are legally available will be used to 
redeem the maximum possible number of such shares ratably among the holder(s) 
of such shares to be 

                                       5

<PAGE>

redeemed such that an equal percentage of the number of shares held by each 
holder of Series AA Preferred Stock is redeemed (provided that this 
Corporation shall have no obligation to issue or redeem any fractional 
shares). The shares of Series AA Preferred Stock not redeemed shall remain 
outstanding and entitled to all the rights and preferences provided herein.  
Subject to the rights of series of Preferred Stock that may from time to time 
come into existence, at any time thereafter when additional funds of this 
Corporation are legally available for the redemption of shares of Series AA 
Preferred Stock, such funds will immediately be used to redeem the balance of 
the shares that this Corporation has become obliged to redeem on any 
Corporation Redemption Date but that it has not redeemed.

          (b)  REDEMPTION AT OPTION OF SHAREHOLDERS.

               (i)  Subject to the rights of series of Preferred Stock that 
may from time to time come into existence, at any time on or after March 9, 
2005, provided that this Corporation shall have received a written request 
from the holders of not less than a majority of the then outstanding Series 
AA Preferred Stock that a specified percentage of such holders' shares of 
Series AA Preferred Stock be redeemed, and concurrently with surrender by 
such holders of the certificates representing such shares, this Corporation 
shall, to the extent it may lawfully do so, redeem the shares specified in 
such request by paying in cash therefor a sum per share equal to (A) $30.59 
per share of Series AA Preferred Stock (as adjusted for any stock splits, 
stock dividends, recapitalizations or the like) plus (B) accrued but unpaid 
dividends on such share (the "Series AA Redemption Price"); provided, 
however, in no event shall this Corporation be required to redeem more than 
817,261 shares of Series AA Preferred Stock (as adjusted for any stock 
splits, stock dividends, recapitalizations or the like) during any twelve 
month period.  Any request made pursuant to this subsection 3(b)(i) shall be 
delivered at least one hundred and eighty (180) days prior to the date on 
which the redemption is requested to occur (a "Shareholder Redemption Date"). 
Any redemption of Series AA Preferred Stock effected pursuant to this 
subsection 3(b)(i) shall be made on a pro rata basis among the holders of the 
Series AA Preferred Stock in proportion to the number of shares of Series AA 
Preferred Stock proposed to be redeemed by such holders.

               (ii) Subject to the rights of series of Preferred Stock that 
may from time to time come into existence, at least twenty (20) but no more 
than thirty (30) days prior to a Shareholder Redemption Date, written notice 
shall be personally delivered, sent by reliable international courier, or 
sent by confirmed facsimile to each holder of record (at the close of 
business on the business day next preceding the day on which notice is given) 
of the Series AA Preferred Stock to be redeemed, at the address last shown on 
the records of this Corporation for such holder, notifying such holder of the 
redemption to be effected on the Shareholder Redemption Date, specifying the 
number of shares to be redeemed from such holder, the Shareholder Redemption 
Date, the Series AA Redemption Price, the place at which payment may be 
obtained and calling upon such holder to surrender to this Corporation, in 
the manner and at the place designated, his, her or its certificate or 
certificates representing the shares to be redeemed (the "Shareholder 
Redemption Notice").  Except as provided in subsection (3)(b)(iii), on or 
after the Shareholder Redemption Date, each holder of Series AA Preferred 
Stock to be redeemed on such Redemption Date shall surrender to this 
Corporation the certificate or 

                                       6

<PAGE>

certificates representing such shares, in the manner and at the place 
designated in the Shareholder Redemption Notice, and thereupon the Series AA 
Redemption Price for such shares shall be payable to the order of the person 
whose name appears on such certificate or certificates as the owner thereof 
and each surrendered certificate shall be cancelled.  In the event less than 
all the shares represented by any such certificate are redeemed, a new 
certificate shall be issued representing the unredeemed shares.

               (iii)     From and after the Shareholder Redemption Date, 
unless there shall have been a default in payment of the Series AA Redemption 
Price, all rights of the holders of shares of Series AA Preferred Stock 
designated for redemption on the Shareholder Redemption Date in the 
Shareholder Redemption Notice as holders of Series AA Preferred Stock (except 
the right to receive the Series AA Redemption Price without interest upon 
surrender of their certificate or certificates) shall cease with respect to 
such shares, and such shares shall not thereafter be transferred on the books 
of this Corporation or be deemed to be outstanding for any purpose 
whatsoever.  Subject to the rights of series of Preferred Stock that may from 
time to time come into existence, if the funds of this Corporation legally 
available for redemption of shares of Series AA Preferred Stock on the 
Shareholder Redemption Date are insufficient to redeem the total number of 
shares of Series AA Preferred Stock to be redeemed on such date, those funds 
that are legally available will be used to redeem the maximum possible number 
of such shares ratably among the holders of such shares to be redeemed such 
that an equal percentage of the number of shares held by each holder of 
Series AA Preferred Stock is redeemed (provided that this Corporation shall 
have no obligation to issue or redeem any fractional shares).  The shares of 
Series AA Preferred Stock not redeemed shall remain outstanding and entitled 
to all the rights and preferences provided herein.  Subject to the rights of 
series of Preferred Stock that may from time to time come into existence, at 
any time thereafter when additional funds of this Corporation are legally 
available for the redemption of shares of Series AA Preferred Stock, such 
funds will immediately be used to redeem the balance of the shares that this 
Corporation has become obliged to redeem on the Shareholder Redemption Date 
but that it has not redeemed.

          4.   CONVERSION.  The holders of the Series AA Preferred Stock 
shall have conversion rights as follows (the "Conversion Rights"):

          (a)  RIGHT TO CONVERT.  Each share of Series AA Preferred Stock 
shall be convertible, at the option of the holder thereof, at any time after 
the Purchase Date of such share and on or prior to the second trading day 
prior to the Redemption Date, if any, as may have been fixed in any 
Redemption Notice with respect to such share of the Series AA Preferred 
Stock, at the office of this Corporation or any transfer agent for such 
stock, into such number of fully paid and nonassessable shares of Common 
Stock as is determined by dividing the Original Series AA Issue Price by the 
Conversion Price applicable to such share, determined as hereafter provided, 
in effect on the date the certificate is surrendered for conversion (the 
"Conversion Ratio").  The initial Conversion Price per share for shares of 
Series AA Preferred Stock shall be $39.77 per share; provided, however, that 
the Conversion Price for the Series AA Preferred Stock shall be subject to 
adjustment as set forth in subsection 4(d).


                                       7

<PAGE>

          (b)  AUTOMATIC CONVERSION.  Each share of Series AA Preferred Stock 
shall automatically be converted into shares of Common Stock at the 
Conversion Ratio at the time in effect for such Series AA Preferred Stock 
immediately upon the date specified by written consent or agreement of the 
holders of a majority of the then outstanding shares of Series AA Preferred 
Stock.

          (c)  MECHANICS OF CONVERSION.  Before any holder of Series AA 
Preferred Stock shall be entitled to convert the same into shares of Common 
Stock, he or she shall surrender the certificate or certificates therefor, 
duly endorsed, at the office of this Corporation or of any transfer agent for 
the Series AA Preferred Stock, and shall give written notice to this 
Corporation at its principal corporate office, of the election to convert the 
same and shall state therein the name or names in which the certificate or 
certificates for shares of Common Stock are to be issued.  This Corporation 
shall, as soon as practicable thereafter, issue and deliver at such office to 
such holder of Series AA Preferred Stock, or to the nominee or nominees of 
such holder, a certificate or certificates for the number of shares of Common 
Stock to which such holder shall be entitled as aforesaid. Such conversion 
shall be deemed to have been made immediately prior to the close of business 
on the date of such surrender of the shares of Series AA Preferred Stock to 
be converted, and the person or persons entitled to receive the shares of 
Common Stock issuable upon such conversion shall be treated for all purposes 
as the record holder or holders of such shares of Common Stock as of such 
date.  If the conversion is in connection with an underwritten offering of 
securities registered pursuant to the Securities Act of 1933, the conversion 
may, at the option of any holder tendering Series AA Preferred Stock for 
conversion, be conditioned upon the closing with the underwriters of the sale 
of securities pursuant to such offering, in which event the persons entitled 
to receive the Common Stock upon conversion of the Series AA Preferred Stock 
shall not be deemed to have converted such Series AA Preferred Stock until 
immediately prior to the closing of such sale of securities.

          (d)  CONVERSION PRICE ADJUSTMENTS OF PREFERRED STOCK FOR SPLITS, 
STOCK DIVIDENDS, COMBINATIONS AND THE LIKE.  The Conversion Price of the 
Series AA Preferred Stock shall be subject to adjustment from time to time as 
follows:

               (i)  In the event this Corporation should at any time or from 
time to time after the Purchase Date fix a record date for the effectuation 
of a split or subdivision of the outstanding shares of Common Stock or the 
determination of holders of Common Stock entitled to receive a dividend or 
other distribution payable in additional shares of Common Stock or other 
securities or rights convertible into, or entitling the holder thereof to 
receive directly or indirectly, additional shares of Common Stock 
(hereinafter referred to as "Common Stock Equivalents") without payment of 
any consideration by such holder for the additional shares of Common Stock or 
the Common Stock Equivalents (including the additional shares of Common Stock 
issuable upon conversion or exercise thereof), then, as of such record date 
(or the date of such dividend distribution, split or subdivision if no record 
date is fixed), the Conversion Price of the Series AA Preferred Stock shall 
be appropriately decreased so that the number of shares of Common Stock 
issuable on conversion of each share of such series shall be increased in 
proportion to such increase of the aggregate of shares of Common Stock 
outstanding and those issuable with respect to such Common Stock Equivalents.

                                       8

<PAGE>

               (ii) If the number of shares of Common Stock outstanding at 
any time after the Purchase Date is decreased by a combination of the 
outstanding shares of Common Stock, then, following the record date of such 
combination, the Conversion Price for the Series AA Preferred Stock shall be 
appropriately increased so that the number of shares of Common Stock issuable 
on conversion of each share of such series shall be decreased in proportion 
to such decrease in outstanding shares.

          (e)  OTHER DISTRIBUTIONS.  In the event this Corporation shall 
declare a distribution payable in securities of other persons, evidences of 
indebtedness issued by this Corporation or other persons, assets (excluding 
cash dividends) or other options or rights not referred to in subsection 
4(d)(i), then, in each such case for the purpose of this Subsection 4(e), the 
holders of the Series AA Preferred Stock shall be entitled to a proportionate 
share of any such distribution as though they were the holders of the number 
of shares of Common Stock of this Corporation into which their shares of 
Series AA Preferred Stock are convertible as of the record date fixed for the 
determination of the holders of Common Stock of this Corporation entitled to 
receive such distribution. 

          (f)  RECAPITALIZATIONS.  If at any time or from time to time there 
shall be a recapitalization of the Common Stock (other than a subdivision, 
combination or merger or sale of assets transaction provided for elsewhere in 
this Section 4 or Section 2) provision shall be made so that the holders of 
the Series AA Preferred Stock shall thereafter be entitled to receive upon 
conversion of the Series AA Preferred Stock the number of shares of stock or 
other securities or property of this Corporation or otherwise, to which a 
holder of Common Stock deliverable upon conversion would have been entitled 
on such recapitalization.  In any such case, appropriate adjustment shall be 
made in the application of the provisions of this Section 4 with respect to 
the rights of the holders of the Series AA Preferred Stock after the 
recapitalization to the end that the provisions of this Section 4 (including 
adjustment of the Conversion Price then in effect and the number of shares 
purchasable upon conversion of the Series AA Preferred Stock) shall be 
applicable after that event as nearly equivalent as may be practicable.

          (g)  NO IMPAIRMENT.  This Corporation will not, by amendment of its 
Amended and Restated Articles of Incorporation or through any reorganization, 
recapitalization, transfer of assets, consolidation, merger, dissolution, 
issue or sale of securities or any other voluntary action, avoid or seek to 
avoid the observance or performance of any of the terms to be observed or 
performed hereunder by this Corporation, but will at all times in good faith 
assist in the carrying out of all the provisions of this Section 4 and in the 
taking of all such action as may be necessary or appropriate in order to 
protect the Conversion Rights of the holders of the Series AA Preferred Stock 
against impairment.

          (h)  NO FRACTIONAL SHARES AND CERTIFICATE AS TO ADJUSTMENTS.

               (i)  No fractional shares shall be issued upon the conversion 
of any share or shares of the Series AA Preferred Stock, and the number of 
shares of Common Stock to be issued shall be rounded down to the nearest 
whole share.  This Corporation shall provide the holder of any fractional 
interest with an amount of cash equal to the fair market value of one 

                                       9

<PAGE>

share of this Corporation's Common Stock multiplied by such fractional 
interest.  Whether or not fractional shares are issuable upon such conversion 
shall be determined on the basis of the total number of shares of Series AA 
Preferred Stock the holder is at the time converting into Common Stock and 
the number of shares of Common Stock issuable upon such aggregate conversion.

               (ii) Upon the occurrence of each adjustment or readjustment of 
the Conversion Price of Series AA Preferred Stock pursuant to this Section 4, 
this Corporation, at its expense, shall promptly compute such adjustment or 
readjustment in accordance with the terms hereof and prepare and furnish to 
each holder of Series AA Preferred Stock a certificate setting forth such 
adjustment or readjustment and showing in detail the facts upon which such 
adjustment or readjustment is based.  This Corporation shall, upon the 
written request at any time of any holder of Series AA Preferred Stock, 
furnish or cause to be furnished to such holder a like certificate setting 
forth (A) such adjustment and readjustment, (B) the Conversion Price for such 
series of Preferred Stock at the time in effect, and (C) the number of shares 
of Common Stock and the amount, if any, of other property that at the time 
would be received upon the conversion of a share of Series AA Preferred Stock.

          (i) NOTICES OF RECORD DATE.  In the event of any taking by this 
Corporation of a record of the holders of any class of securities for the 
purpose of determining the holders thereof who are entitled to receive any 
dividend (other than a cash dividend) or other distribution, any right to 
subscribe for, purchase or otherwise acquire any shares of stock of any class 
or any other securities or property, or to receive any other right, this 
Corporation shall mail to each holder of Series AA Preferred Stock, at least 
twenty (20) days prior to the date specified therein, a notice specifying the 
date on which any such record is to be taken for the purpose of such 
dividend, distribution or right, and the amount and character of such 
dividend, distribution or right.

          (j)  RESERVATION OF STOCK ISSUABLE UPON CONVERSION.  This 
Corporation shall at all times reserve and keep available out of its 
authorized but unissued shares of Common Stock, solely for the purpose of 
effecting the conversion of the shares of the Series AA Preferred Stock, such 
number of its shares of Common Stock as shall from time to time be sufficient 
to effect the conversion of all outstanding shares of the Series AA Preferred 
Stock; and if at any time the number of authorized but unissued shares of 
Common Stock shall not be sufficient to effect the conversion of all then 
outstanding shares of the Series AA Preferred Stock, in addition to such 
other remedies as shall be available to the holder of such Preferred Stock, 
this Corporation will take such corporate action as may, in the opinion of 
its counsel, be necessary to increase its authorized but unissued shares of 
Common Stock to such number of shares as shall be sufficient for such 
purposes, including, without limitation, engaging in best efforts to obtain 
the requisite shareholder approval of any necessary amendment to this 
Certificate of Designation or the Amended and Restated Articles of 
Incorporation.

          (k)  NOTICES.  Any notice required by the provisions of this 
Section 4 to be given to the holders of shares of Series AA Preferred Stock 
shall be deemed given if deposited in the United States mail, postage 
prepaid, and addressed to each holder of record at his address appearing on 
the books of this Corporation.

                                      10

<PAGE>

          5.   VOTING RIGHTS.  The holder of each share of Series AA 
Preferred Stock shall have the right to one vote for each share of Common 
Stock into which such Series AA Preferred Stock could then be converted at 
the record date for determination of the shareholders entitled to vote 
thereon, and with respect to such vote, such holder shall have full voting 
rights and powers equal to the voting rights and powers of the holders of 
Common Stock, and shall be entitled, notwithstanding any provision hereof, to 
notice of any shareholders' meeting in accordance with the bylaws of this 
Corporation, and shall be entitled to vote, together with holders of Common 
Stock, with respect to any question upon which holders of Common Stock have 
the right to vote and otherwise as required by law. Fractional votes shall 
not, however, be permitted and any fractional voting rights available on an 
as-converted basis (after aggregating all shares into which shares of Series 
AA Preferred Stock held by each holder could be converted) shall be rounded 
to the nearest whole number (with one-half being rounded upward).  

4.   We further declare under penalty of perjury under the laws of the State of
     California that the matters set forth in this certificate are true and
     correct of our own knowledge. 

                                      11

<PAGE>

          RESOLVED FURTHER, that the officers of the Corporation are each
     authorized to execute, verify and file in the office of the California
     Secretary of State a Certificate of Determination in accordance with
     this resolution and California law.

Executed on March __, 1998 at Menlo Park, California.


                                   --------------------------------
                                   Stephen P. A. Fodor
                                   President and Chief Executive Officer


                                   --------------------------------
                                   Edward M. Hurwitz
                                   Chief Financial Officer

                                      12


<PAGE>

                           SERIES AA PREFERRED STOCK
                              PURCHASE AGREEMENT

          This SERIES AA PREFERRED STOCK PURCHASE AGREEMENT (the "Agreement") 
dated March 9, 1998 is entered into by and between Affymetrix, Inc., a 
California corporation (together with its successors, the "Company"), and 
Glaxo Wellcome Americas Inc., a Delaware corporation ("Investor").

          Unless otherwise defined herein, capitalized terms used herein and 
not defined herein shall have the meanings given to them under the Securities 
Act of 1933, as amended (the "Securities Act").

          The parties hereto agree as follows:

          1.   PURCHASE AND SALE.  In consideration of and upon the basis of 
the representations, warranties and agreements and subject to the terms and 
conditions set forth in this Agreement:

               a.   Investor agrees to purchase from the Company and the 
Company agrees to sell to Investor, on the Closing Date specified in Section 
2 hereof, 1,634,522 shares of the Company's Series AA Preferred Stock (the 
"Preferred Shares") for a price per share equal to $30.59 (the "Purchase 
Price").  On or before the Closing Date (as defined below), the Company will 
have authorized the sale and issuance to Investor of the Preferred Shares, 
having the rights, preferences and priviledges set forth in the Certificate 
of Determination attached hereto as EXHIBIT A (the "Certificate of 
Determination").

               b.   The term "Conversion Stock" shall mean any shares of the 
Company's common stock, no par value per share (the "Common Stock") issued or 
to be issued to Investor upon conversion of the Preferred Shares pursuant to 
the terms of this Agreement and the Certificate of Determination.

          2.   CLOSING.

               a.   The closing of the sale of the Preferred Shares (the 
"Closing") shall take place on March ___, 1998 upon satisfaction or, if 
applicable, waiver of the conditions set forth in Sections 6 and 7 hereof, or 
at such other date and time as the Investor and the Company shall mutually 
agree (such date and time being referred to herein as the "Closing Date").

               b.   At the Closing, the Company shall deliver to Investor a 
certificate representing the Preferred Shares that Investor is purchasing, 
duly registered on the books of the Company in the name of Investor, against 
payment by Investor of the Purchase Price by check or wire transfer of 
immediately available funds.

<PAGE>

          3.   REPRESENTATIONS AND WARRANTIES OF THE COMPANY.  Except as set 
forth in the Disclosure Letter delivered to Investor by the Company 
concurrently with this Agreement, the Company hereby represents and warrants 
to Investor as follows:

               a.   The Company is a corporation duly organized, validly 
existing and in good standing under the laws of the State of California and 
has all requisite corporate power and authority to carry on its business as 
now conducted and as proposed to be conducted.  The Company is duly qualified 
to transact business and is in good standing in each jurisdiction in which 
the failure to so qualify would have a material adverse effect on its 
business or properties.

               b.   All corporate action on the part of the Company, its 
officers and directors necessary for the authorization, execution and 
delivery of this Agreement, the Voting Trust Agreement dated of the Closing 
Date between the Company, Wachovia Bank, N.A. (the "Trustee") and Investor 
("Voting Trust Agreement") in the form attached hereto as EXHIBIT B, the 
Amendment to Governance Agreement dated as of the Closing Date between the 
Company and Glaxo Wellcome PLC ("Glaxo") and accepted and agreed to by the 
Investor (the "Amendment") in the form attached hereto as EXHIBIT C, the 
performance of all obligations of the Company hereunder and thereunder, and 
the authorization, issuance (or reservation for issuance), sale and delivery 
of the Preferred Shares being sold hereunder and the Common Stock issuable 
upon conversion of the Preferred Shares has been taken or will be taken prior 
to the Closing, and this Agreement, the Voting Trust Agreement and the 
Amendment constitute valid and legally binding obligations of the Company, 
enforceable in accordance with their respective terms, except (i) as limited 
by applicable bankruptcy, insolvency, reorganization, moratorium, and other 
laws of general application affecting enforcement of creditors' rights 
generally and (ii) as limited by laws relating to the availability of 
specific performance, injunctive relief, or other equitable remedies.

               c.   The Company is not in violation or default of any 
provision of its Amended and Restated Articles of Incorporation or bylaws, or 
of any judgment, order, writ, or decree by which it is bound.  The Company is 
not in violation or default in any material respect of any instrument or 
contract to which it is a party or by which it is bound, or, to its 
knowledge, of any provision of any federal or state statute, rule or 
regulation applicable to the Company.  The execution, delivery and 
performance of this Agreement, the Voting Trust Agreement, and the Amendment, 
and the consummation of the transactions contemplated hereby and thereby will 
not result in any such violation or be in conflict with or constitute, with 
or without the passage of time and giving of notice, either a default under 
any such provision, instrument, judgment, order, writ, decree or contract or 
an event that results in the creation of any lien, charge or encumbrance upon 
any assets of the Company or the suspension, revocation, impairment, 
forfeiture, or nonrenewal of any material permit, license, authorization, or 
approval applicable to the Company, its business or operations or any of its 
assets or properties.

               d.   Except as may be required under the Hart-Scott-Rodino 
Antitrust Improvements Act of 1976, as amended ("HSR Act"), no consent, 
approval, order or authorization of, or registration, qualification, 
designation, declaration or filing with, any federal, state or local 
governmental authority on the part of the Company is required in connection 
with the consummation of the transactions contemplated by this Agreement, 
except (i) the filing of the  

                                       2

<PAGE>

Certificate of Determination with the Secretary of State of California; and 
(ii) the filing pursuant to Regulation D promulgated by the Securities and 
Exchange Commission under the Securities Act, which filing will be effected 
within 15 days of the sale of the Preferred Shares hereunder, or such other 
post-closing filings as may be required.

               e.   Except as disclosed in the SEC Filings (as defined below) 
and in the Company's registration statement on Form S-3 as filed with the SEC 
on October 17, 1997 (the "S-3"), (i) there is no action, suit, proceeding or 
investigation pending or, to the Company's knowledge, currently threatened 
against the Company that questions the validity of this Agreement, the Voting 
Trust Agreement or the Amendment, or the right of the Company to enter into 
such agreements, or to consummate the transactions contemplated hereby or 
thereby, and (ii) there is no action, suit, proceeding or investigation 
pending or, to the knowledge of the Company, currently threatened in writing 
against the Company, or against any executive officer or director of the 
Company which might result, either individually or in the aggregate, in any 
material adverse change in the business, properties, financial condition or 
operating results of the Company, as such business is presently conducted.

               f.   The Company has timely filed all filings with the United 
States Securities and Exchange Commission (the "SEC") under the Securities 
Act or under Section 13(a) or 15(d) of the Securities Exchange Act of 1934, 
as amended (the "Exchange Act") or under the rules and regulations 
promulgated by the SEC (any such filing, an "SEC Filing") required to be 
filed by the Company pursuant to such acts and no SEC Filing contained, on 
the date on which such document was filed with the SEC, any untrue statement 
of a material fact or omitted to state any material fact required to be 
stated therein or necessary in order to make the statements, in the light of 
the circumstances under which they were made, not misleading.  The financial 
statements of the Company included in SEC Filings (including any similar 
documents filed after the date of this Agreement) comply as to form in all 
material respects with applicable accounting requirements and the published 
rules and regulations of the SEC with respect thereto, have been prepared in 
accordance with generally accepted accounting principles (except, in the case 
of unaudited statements, as permitted by Form 10-Q of the SEC) applied on a 
consistent basis during the periods involved (except as may be indicated in 
the notes thereto), and fairly present the consolidated financial position of 
Company and its consolidated subsidiaries as of the dates thereof and the 
consolidated results of their operations and cash flows for the periods then 
ended (subject, in the case of unaudited statements, to normal year-end audit 
adjustments). 

               g.   Since the date of the Company's most recent quarterly 
report on Form 10-Q or most recent periodic report on Form 8-K filed with the 
SEC, there has not been any development that has not otherwise been publicly 
disclosed that is reasonably likely to result in any material adverse change 
in the financial condition or results of operations of the Company.

               h.   Except as disclosed in the SEC Filings and the S-3 and as 
contemplated hereby, the Company has not granted or agreed to grant any 
registration rights, including piggy-back rights, to any person or entity.

                                       3

<PAGE>

               i.   As of February 28, 1998, the authorized capital stock of 
the Company consisted of 27,500,000 shares of Preferred Stock, none of which 
were issued and outstanding, and 50,000,000 shares of Common Stock, 
22,842,355 shares of which were issued and outstanding (the "Preferred Stock" 
and the "Common Stock" are collectively referred to herein as the "Capital 
Stock").  All of the issued and outstanding shares of Capital Stock have been 
duly authorized, validly issued and are fully paid and nonassessable.  There 
has been no material change in the capitalization of the Company from 
February 28, 1998 to the date of this Agreement.

               j.   The Preferred Shares that are being purchased by the 
Investor hereunder, when issued, sold or delivered in accordance with the 
terms hereof, for the consideration expressed herein, and the shares of 
Common Stock issuable upon conversion of the Preferred Shares, upon issuance 
in accordance with the terms of the Certificate of Determination, will be 
duly and validly issued, fully paid and nonassessable and will be free of any 
liens and encumbrances created by the Company and, subject to the accuracy of 
the representations of the Investor in this Agreement, will be issued in 
compliance with all applicable federal and state securities laws.

          4.   REPRESENTATIONS AND WARRANTIES OF INVESTOR.  Investor hereby 
represents and warrants to the Company on the date hereof, and agrees with 
the Company (unless otherwise specified as provided in the paragraphs below), 
as follows:

               a.   Investor understands that no United States federal or 
state agency has passed on, reviewed or made any recommendation or 
endorsement of the Preferred Shares or the Conversion Stock.

               b.   Investor has full power and authority to enter into this 
Agreement, the Voting Trust Agreement and the Amendment, and such Agreements 
constitute its valid and legally binding obligation, enforceable in 
accordance with their terms, except (i) as limited by applicable bankruptcy, 
insolvency, reorganization, moratorium, and other laws of general application 
affecting enforcement of creditors' rights generally and (ii) as limited by 
laws relating to the availability of specific performance, injunctive relief, 
or other equitable remedies.

               c.   This Agreement is made with Investor in reliance upon 
Investor's representation to the Company, which by Investor's execution of 
this Agreement Investor hereby confirms, that the Preferred Shares to be 
received by Investor and the Conversion Stock issuable upon conversion 
thereof (collectively, the "Securities") will be acquired for investment for 
Investor's own account, not as a nominee or agent, and not with a view to the 
resale or distribution of any part thereof, and that Investor has no present 
intention of selling, granting any participation in, or otherwise 
distributing the same.  By executing this Agreement, Investor further 
represents that Investor does not have any contract, undertaking, agreement 
or arrangement with any person to sell, transfer or grant participations to 
such person or to any third person, with respect to any of the Securities.

               d.   Investor is an investor in securities of companies in the 
development stage and acknowledges that it can bear the economic risk of its 
investment, and has 

                                       4

<PAGE>

such knowledge and experience in financial or business matters that it is 
capable of evaluating the merits and risks of the investment in the Preferred 
Shares.  Investor also represents it has not been organized for the purpose 
of acquiring the Preferred Shares.

               e.   Investor is an "accredited investor" within the meaning 
of SEC Rule 501(a) of Regulation D, as presently in effect.

               f.   Investor understands that the Preferred Shares are being 
offered and sold in reliance on a transactional exemption from the 
registration requirements of Federal and state securities laws and that the 
Company is relying upon the truth and accuracy of the representations, 
warranties, agreements, acknowledgments and understandings of the Investor 
set forth herein in order to determine the applicability of such exemptions 
and the suitability of the Investor to acquire the Preferred Shares.

               g.   Investor understands that the Securities it is purchasing 
are characterized as "restricted securities" under the federal securities 
laws inasmuch as they are being acquired from the Company in a transaction 
not involving a public offering and that under such laws and applicable 
regulations such securities may be resold without registration under the 
Securities Act, only in certain limited circumstances.  In this connection, 
Investor represents that it is familiar with SEC Rule 144, as presently in 
effect, and understands the resale limitations imposed thereby and by the 
Securities Act.

               h.   Without in any way limiting the representations set forth 
above, Investor further agrees not to make any disposition of all or any 
portion of the Securities unless and until the transferee has agreed in 
writing for the benefit of the Company to be bound by the terms of this 
Agreement provided and to the extent such terms are then applicable, and: 

                    (1)  There is then in effect a Registration Statement 
under the Securities Act covering such proposed disposition and such 
disposition is made in accordance with such Registration Statement; or

                    (2)  (i) Investor shall have notified the Company of the 
proposed disposition and shall have furnished the Company with a detailed 
statement of the circumstances surrounding the proposed disposition, and (ii) 
if reasonably requested by the Company, Investor shall have furnished the 
Company with an opinion of counsel, reasonably satisfactory to the Company 
that such disposition will not require registration of such shares under the 
Securities Act.  It is agreed that the Company will not require opinions of 
counsel for transactions made pursuant to Rule 144 except in circumstances 
that require a determination of an entity's status as an "affiliate".

               i.   It is understood that the certificates evidencing the 
Securities will bear the following legends:

          "THESE SECURITIES HAVE NOT BEEN REGISTERED UNDER THE SECURITIES ACT 
OF 1933, AS AMENDED.  THEY MAY NOT BE SOLD, OFFERED FOR SALE, PLEDGED OR 
HYPOTHECATED IN THE ABSENCE OF A REGISTRATION 

                                       5

<PAGE>

STATEMENT IN EFFECT WITH RESPECT TO THE SECURITIES UNDER SUCH ACT OR AN 
OPINION OF COUNSEL SATISFACTORY TO THE COMPANY THAT SUCH REGISTRATION IS NOT 
REQUIRED OR UNLESS SOLD PURSUANT TO RULE 144 OF SUCH ACT."

          "THE SHARES REPRESENTED BY THIS CERTIFICATE ARE SUBJECT TO 
RESTRICTIONS ON VOTING AND TRANSFER AS SET FORTH IN THE VOTING TRUST 
AGREEMENT, DATED AS OF MARCH__, 1998, A COPY OF WHICH IS AVAILABLE FROM THE 
COMPANY AND ANY SUCCESSOR THERETO."

               j.   The execution, delivery and performance of this 
Agreement, the Voting Trust Agreement and the Amendment, and the consummation 
by Investor of the transactions contemplated hereby and thereby do not and 
will not (i) result in a violation of Investor's charter documents or bylaws 
or (ii) conflict with any material agreement, indenture or instrument to 
which Investor is a party, or (iii) result in a violation of any order, 
judgment or decree of any court or governmental agency applicable to Investor 
or, to the Investor's knowledge, of any law, rule, or regulation.  Except as 
may be required under the HSR Act, Investor is not required to obtain any 
consent or authorization of any governmental agency in order for it to 
perform its obligations under this Agreement, under the Voting Trust 
Agreement or under the Amendment.

          5.   COVENANTS.

               a.   The Company covenants and agrees with Investor as follows:

                    (1)  For so long as any of the Preferred Shares are 
outstanding, and in any case for a period of 40 calendar days thereafter, the 
Company will cause its Common Stock to continue to be registered under 
Sections 12(b) or 12(g) of the Exchange Act, will comply in all respects with 
its reporting and filing obligations under said act, and will not take any 
action or file any document (whether or not permitted by the Act or the 
Exchange Act or the rules thereunder) to terminate or suspend its reporting 
and filing obligations under said acts, except as permitted herein.  For so 
long as any of the Preferred Shares are outstanding, and in any case for a 
period of 40 calendar days thereafter, the Company will use its best efforts 
to continue the listing or trading of its Common Stock on Nasdaq National 
Market ("Nasdaq") or on a national securities exchange (as defined in the 
Exchange Act) and will comply in all respects with the Company's reporting, 
filing and other obligations under the bylaws or rules of the National 
Association of Securities Dealers and Nasdaq.  Notwithstanding the foregoing, 
the provisions of this subsection shall not in any way restrict the Company's 
ability to negotiate and consummate the consolidation, reorganization or 
merger of the Company with or into any other corporation or corporations or a 
sale, conveyance, or other disposition of all or substantially all of the 
Company's property or business

                    (2)  The Company will (i) comply with the terms and 
conditions of the Preferred Shares as set forth in the Certificate of 
Determination and (ii) not amend the Certificate of Determination without 
Investor's express written consent.

                                       6

<PAGE>

                    (3)  For so long as any of the Preferred Shares are 
outstanding, the Company shall at all times reserve and keep available, free 
from preemptive rights, out of its authorized but unissued Common Stock, for 
issuance upon conversion of such Preferred Shares, not less than the maximum 
number of shares of Common Stock then so issuable in exchange for all 
Preferred Shares that have been issued pursuant to this Agreement and not 
previously converted. 

               b.   The Investor covenants and agrees with the Company that 
neither Investor nor any of Investor's affiliates nor any person acting on 
its or their behalf will at any time offer or sell any Preferred Shares or 
any Conversion Stock other than pursuant to registration under the Securities 
Act or pursuant to an available exemption therefrom.

               c.   The covenants contained in this Section 5 shall terminate 
upon the consummation of any consolidation, reorganization or merger of the 
Company with or into any other corporation or corporations or a sale, 
conveyance, or other disposition of all or substantially all of the Company's 
property or business.

               d.   With a view to making available the benefits of certain 
rules and regulations of the SEC that may at any time permit the sale of the 
restricted securities to the public without registration, the Company agrees 
to:

                    (1)  Make and keep public information available, as those 
terms are understood and defined in Rule 144 under the Securities Act, at all 
times after the effective date of the first registration under the Securities 
Act filed by the Company for an offering of its securities to the general 
public;

                    (2)  Use its best efforts to then file with the SEC in a 
timely manner all reports and other documents required of the Company under 
the Securities Act and the Exchange Act; and

                    (3)  So long as Investor owns any Preferred Shares, to 
furnish to the Investor upon request, a written statement by the Company as 
to its compliance with the reporting requirements of said Rule 144 and of the 
Securities Act and of the Exchange Act, a copy of the most recent annual or 
quarterly report of the Company, and such other reports and documents of the 
Company as the Investor may reasonably request in availing itself of any rule 
or regulation of the SEC allowing the Investor to sell any such securities 
without registration.

               e.   HSR ACT FILING.  Each of the Company and Investor shall 
(i) promptly make or cause to be made the filings required of such party or 
any of its affiliates or subsidiaries under the HSR Act with respect to the 
purchase of the Preferred Shares, and (ii) comply at the earliest practicable 
date with any request under the HSR Act for additional information, 
documents, or other material received by such party or any of its affiliates 
or subsidiaries from the Federal Trade Commission or the Department of 
Justice or other appropriate regulatory agency in respect of such filings and 
the sale of the Preferred Shares.  Each of the Company and Investor shall use 
commercially reasonable efforts to take such action as may be required to 
cause the expiration of the notice periods under the HSR Act with respect 

                                       7

<PAGE>

to the sale of Preferred Shares as soon as possible after the execution of 
this Agreement.  The Company agrees to pay any filing fees in connection with 
all filings required under the HSR Act in connection with the transaction 
contemplated hereby, and agrees to pay reasonable legal counsel fees and 
expenses not to exceed $5,000 incurred in connection with such filings.

          6.   CONDITIONS PRECEDENT TO INVESTOR'S OBLIGATIONS.  The 
obligations of Investor under subsection 1.a of this Agreement are subject to 
the fulfillment on or before the Closing of each of the following conditions, 
unless expressly waived in writing by the Investor:

               a.   The representations and warranties of the Company 
contained in Section 3 shall be true on and as of the Closing with the same 
effect as though such representations and warranties had been made on and as 
of the date of such Closing, except for representations and warranties made 
as of a particular date, which shall be true and correct as of such date.

               b.   The Company shall have performed and complied with all 
agreements, obligations and conditions contained in this Agreement that are 
required to be performed or complied with by it on or before the Closing.

               c.   The President of the Company shall deliver to Investor at 
the Closing a certificate stating that the conditions specified in Sections 
6.a and 6.b have been fulfilled and stating that there shall have been no 
material adverse change in the business, affairs, operations, properties, 
assets or financial condition of the Company since the date of this Agreement.

               d.   The Company shall have caused the Certificate of 
Determination to be filed with the Secretary of State of the State of 
California in accordance with the laws thereof.

               e.   No statute, rule, regulation, executive order, decree, 
ruling or injunction shall have been enacted, entered, promulgated or 
endorsed by any court or governmental authority of competent jurisdiction 
which prohibits the consummation of any of the transactions contemplated by 
this Agreement.

               f.   The applicable waiting period under the HSR Act relating 
to the sale of the Preferred Shares shall have expired or been terminated.

               g.   The Company, the Trustee and Investor shall have entered 
into the Voting Trust Agreement.

               h.   The Company shall have delivered to Investor a 
certificate representing the Preferred Shares, duly registered on the books 
of the Company in the name of the Investor.

               i.   Investor shall have received from Gunderson Dettmer 
Stough Villeneuve Franklin & Hachigian, LLP, counsel for the Company, an 
opinion, dated as of the Closing Date, in substantially the form attached 
hereto as EXHIBIT D.

                                       8

<PAGE>

               j.   The Company and Glaxo shall have entered into the 
Amendment and Investor shall have accepted and agreed to the Amendment.

          7.   CONDITIONS PRECEDENT TO THE COMPANY'S OBLIGATIONS.  The 
obligations of the Company to Investor under this Agreement are subject to 
the fulfillment on or before the Closing of each of the following conditions 
by the Investor, unless expressly waived in writing by the Company:

               a.   The representations and warranties of the Investor 
contained in Section 4 shall be true on and as of the Closing with the same 
effect as though such representations and warranties had been made on and as 
of the date of such Closing, except for representations and warranties made 
as of a particular date, which shall be true and correct as of such date.

               b.   The Investor shall have performed and complied with all 
agreements, obligations and conditions contained in this Agreement that are 
required to be performed or complied with by it on or before the Closing.

               c.   An appropriate officer of Investor shall deliver to the 
Company at the Closing a certificate stating that the conditions specified in 
Sections 7.a and 7.b have been fulfilled.

               d.   No statute, rule, regulation, executive order, decree, 
ruling or injunction shall have been enacted, entered, promulgated or 
endorsed by any court or governmental authority of competent jurisdiction 
which prohibits the consummation of any of the transactions contemplated by 
this Agreement.

               e.   The applicable waiting period under the HSR Act relating 
to the sale of the Preferred Shares shall have expired or been terminated.

               f.   The Company, the Trustee and Investor shall have entered 
into the Voting Trust Agreement.

               g.   The Investor shall have delivered the aggregate Purchase 
Price for the Preferred Shares.

               h.   The Company and Glaxo shall have entered into the 
Amendment and Investor shall have accepted and agreed to the Amendment.

               i.   The Company shall have caused the Certificate of 
Determination to be filed with the Secretary of State of the State of 
California in accordance with the laws thereof.

          8.   FEES AND EXPENSES.  Each of Investor and the Company agrees to 
pay its own expenses incident to the performance of its obligations 
hereunder, including, but not limited to the fees, expenses and disbursements 
of such party's counsel, except as is otherwise expressly provided in this 
Agreement.

                                       9

<PAGE>

          9.   SURVIVAL OF THE REPRESENTATIONS, WARRANTIES, ETC.  The 
respective representations, warranties, and agreements made herein by or on 
behalf of the parties hereto shall remain in full force and effect for a 
period of two years from the Closing Date, regardless of any investigation 
made by or on behalf of the other party to this Agreement or any officer, 
director or employee of, or person controlling or under common control with, 
such party and will survive delivery of and payment for the Preferred Shares 
and any Conversion Stock issuable hereunder.

          10.  TERMINATION.

               a.   This Agreement may be terminated and the transactions 
contemplated by this Agreement may be abandoned at any time prior to the 
Closing as follows:

                    (i)  by mutual written consent of the Company and the 
Investor; or

                    (ii) by either the Company or the Investor if the Closing 
shall not have occurred on or before May 31, 1998 (the "Termination Date"); 
provided, however, that the right to terminate this Agreement under this 
Section 10 shall not be available to any party whose failure to fulfill any 
obligation under this Agreement has been the cause of, or resulted in, the 
failure of the Closing to occur on or before the Termination Date; and 
provided further, that if a request for additional information is received 
from an appropriate regulatory authority pursuant to the HSR Act, such date 
shall be extended to the 90th day following acknowledgment by such regulatory 
authority that Investor and the Company complied with such request. 

          b.   In the event of termination of this Agreement by either the 
Company or Investor as provided in this Section 10, this Agreement shall 
forthwith become void and have no effect, without any liability or obligation 
on the part of the Company or Investor, other than the provisions of this 
Section 10 and Section 12, and except to the extent that such termination 
results from the willful and material breach by a party of any of its 
representations, warranties, covenants or agreements set forth in this 
Agreement.

          11.  NOTICES.  Unless otherwise provided, any notice required or 
permitted under this Agreement shall be given in writing and shall be deemed 
effectively given upon delivery by confirmed facsimile or reliable 
international courier service or upon personal delivery to the party to be 
notified. 

          12.  MISCELLANEOUS.

               a.   This Agreement may be executed in one or more 
counterparts and it is not necessary that signatures of all parties appear on 
the same counterpart, but such counterparts together shall constitute but one 
and the same agreement.

               b.   This Agreement shall inure to the benefit of and be 
binding upon the parties hereto, their respective successors and assigns.

                                      10

<PAGE>

               c.   This Agreement shall be governed by, and construed in 
accordance with, the internal laws of the State of California without regard 
to principles of conflict of laws.

               d.   The provisions of this Agreement are severable, and if 
any clause or provision hereof shall be held invalid, illegal or 
unenforceable in whole or in part, such invalidity or unenforceability shall 
not in any manner affect any other clause or provision of this Agreement.

               e.   The headings of the sections of this document have been 
inserted for convenience of reference only and shall not be deemed to be a 
part of this Agreement.

               f.   This Agreement (including the terms and conditions of the 
Certificate of Determination relating to the Preferred Shares), the Voting 
Trust Agreement and the Amendment constitute the entire agreement and 
supersede all prior agreements and understandings, both written and oral, 
between the parties hereto with respect to the subject matter of this 
Agreement and is not intended to confer upon any person other than the 
parties hereto any rights or remedies hereunder or under the terms of the 
term sheets between such parties.

               g.   The term "affiliate" is used herein as defined in Rule 
144(a)(1) under the Securities Act.

                                       11

<PAGE>

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

                                        AFFYMETRIX, INC.


                                        By:
                                           ---------------------------------
                                        Name:
                                        Title:


                                        GLAXO WELLCOME AMERICAS INC.


                                        By:
                                           ---------------------------------
                                        Name:
                                        Title:

<PAGE>

                                                        EXHIBIT A OF EXHIBIT 10



                  See Exhibit 4 of Form 8-K, March 9, 1998


<PAGE>

                                                        EXHIBIT B OF EXHIBIT 10

                            VOTING TRUST AGREEMENT

          THIS VOTING TRUST AGREEMENT (the "Agreement") is entered into as of 
March __, 1998, by and among Affymetrix, Inc. (the "Company"), Wachovia Bank, 
N.A. (the "Trustee"), and Glaxo Wellcome Americas Inc. ("GWA") as holder of 
the Company's Series AA Preferred Stock.  GWA and transferees of GWA pursuant 
to Section 3 hereof are individually each referred to herein as a "Party" and 
are collectively referred to herein as the "Parties."  The Company's Board of 
Directors is referred to hereto as the "Board."

                                  RECITALS:

          WHEREAS, on the date hereof, GWA purchased 1,634,522 shares of the 
Company's Series AA Preferred Stock pursuant to that certain Series AA 
Preferred Stock Purchase Agreement between the Company and GWA ("Securities 
Purchase Agreement"); and

          WHEREAS, in order to induce the Company to sell shares of Preferred 
Stock to GWA, GWA has agreed to be bound by the terms of this Agreement;

          NOW, THEREFORE, in consideration of the foregoing premises and 
certain other good and valuable consideration, the receipt and sufficiency of 
which are hereby acknowledged, the Parties hereby agree as follows:

          1.   VOTING TRUST CERTIFICATES.  

               (a)   Upon execution of this Agreement, GWA shall deliver to 
the Trustee all certificates held by GWA representing the Shares (as defined 
herein), and the Trustee shall issue and deliver to GWA, a voting trust 
certificate in substantially the form attached hereto as SCHEDULE I (a 
"Voting Trust Certificate"), for the number of Shares owned by GWA and 
transferred to the Trustee.  The Company shall cause such Shares to be 
transferred to the Trustee on the Company's books.  Any Shares acquired by 
GWA after the date hereof shall be issued to the Trustee, who shall, within 
five (5) business days (as defined in the Securities Purchase Agreement), 
issue and deliver to GWA, a Voting Trust Certificate for the number of 
additional Shares so acquired by GWA.  The Trustee shall have no 
responsibility for Shares not delivered to it.

               (b)   The Trustee shall hold the Shares in trust subject to 
the terms of this Agreement.  The Trustee shall distribute all dividends and 
other distributions to GWA or GWA's successors (other than dividends or other 
distributions payable in Shares which shall not be distributed but shall 
remain subject to the terms of this Agreement) in proportion to their 
respective interests as represented by the Voting Trust Certificates.

               (c)   All Voting Trust Certificates will be registered in the 
trust system maintained by the Trustee for that purpose (the "Trust 
Register").  The Trustee may treat the registered holder of each Voting Trust 
Certificate as the absolute owner and holder of the Shares 

<PAGE>

evidenced thereby and of all of the other rights and interests represented 
thereby.  All transfers of Shares will be recorded by the Trustee in the 
Trust Register.

               (d)   If a Voting Trust Certificate is lost, stolen, mutilated 
or destroyed, the Trustee will issue a duplicate Voting Trust Certificate 
upon receipt by the Trustee of evidence satisfactory to the Trustee and the 
Company of the loss, theft, mutilation or destruction, and upon receipt of a 
bond, undertaking or other indemnity reasonably satisfactory to the Trustee 
and the Company.  The Trustee will also keep correct records of account of 
all business transactions with respect to the Voting Trust, which records, 
including the Trust Register, may be inspected by any Party and such Party's 
agents or personal representatives at any time during normal business hours.

               (e)   In the event that during the term of this Agreement, a 
Beneficial Owner elects to convert a portion of such Beneficial Owner's 
Shares into Common Stock, such Beneficial Owner shall deliver to the Trustee, 
(i) a notice containing the identity of the Beneficial Owner and the number 
of Shares to be converted into Common Stock (the "Conversion Shares"), and 
(ii) the original Voting Trust Certificate(s) representing the Conversion 
Shares.  Upon the Trustee's receipt of such notice and the appropriate Voting 
Trust Certificate(s), the Trustee shall, as soon as practicable thereafter, 
(i) deliver the Conversion Shares to the Company (or its designated transfer 
agent) and (ii) issue and deliver to such Beneficial Owner a Voting Trust 
Certificate representing the balance of the shares of Series AA Preferred 
Stock not to be converted into Common Stock, if any, represented by the 
Voting Trust Certificate(s) delivered by the Beneficial Owner to the Trustee 
pursuant to this Section 1(e).  Upon Trustee's delivery of the Conversion 
Shares to the Company (or its designated transfer agent), the Trustee shall 
be fully acquitted and discharged with respect to such Conversion Shares. 
After the Conversion Shares have been delivered to the Company pursuant to 
this Section, the conversion of such shares shall be governed by and pursuant 
to the terms and provisions of the Certificate of Determination of Series AA 
Preferred Stock of the Company (the "Certificate of Determination").

               (f)   In the event that during the term of this Agreement, any 
Shares of a Beneficial Owner are subject to redemption pursuant to Section 
3(a) of the Certificate of Determination, the Company shall deliver the 
Corporation Redemption Notice (as defined in the Certificate of 
Determination) to the Trustee and to each Person set forth in Section 22 
hereof at least twenty (20) but not more than thirty (30) days prior to the 
Corporation Redemption Date (as defined in the Certificate of Determination). 
At least ten (10) days prior to the Corporation Redemption Date, each 
Beneficial Owner shall deliver to the Trustee the original Voting Trust 
Certificate(s) representing the Shares Beneficially Owned by such Person 
along with written instructions to the Trustee to either (i) convert the 
Shares to be redeemed under Section 1(e) of this Agreement or (ii) to 
surrender such Shares for redemption.  The Trustee shall, (i) at least three 
(3) days prior to the Corporation Redemption Date, deliver the certificate(s) 
representing the Shares to be redeemed as set forth in the Corporation 
Redemption Notice (and which have not previously been converted) to the 
Company (or its designated transfer agent) and (ii) as soon as practicable 
thereafter, issue and deliver to such Beneficial Owner a Voting Trust 
Certificate representing the balance of the Shares not to be redeemed, if 
any, represented by the Voting Trust Certificate(s) delivered by the 
Beneficial Owner to the Trustee pursuant to this 

                                       2

<PAGE>

Section 1(f). Upon the Trustee's receipt of the Early Redemption Price or 
Late Redemption Price (as such terms are defined in the Certificate of 
Determination), as the case may be, payable with respect to the Shares 
redeemed, the Trustee shall, as soon as practicable thereafter, deliver the 
Early Redemption Price or Late Redemption Price, as the case may be, payable 
with respect to the Shares redeemed to the Beneficial Owners such that each 
Beneficial Owner receives that portion of the Early Redemption Price or Late 
Redemption Price paid by the Company, as the case may be, equal to the 
proportion of Shares Beneficially Owned by such Beneficial Owner to the total 
number of Shares subject to this Agreement.  Upon Trustee's delivery of the 
Early Redemption Price or Late Redemption Price, as the case may be, payable 
with respect to such Shares to the appropriate Beneficial Owner, the Trustee 
shall be fully acquitted and discharged with respect to such redeemed Shares.

               (g)   In the event that during the term of this Agreement, 
Beneficial Owners holding at least a majority of the then outstanding Shares 
elect to have some or all of such Beneficial Owners' Shares redeemed pursuant 
to the provisions of Section 3(b) of the Certificate of Determination, such 
Beneficial Owners shall deliver to the Trustee and the Company a notice 
containing the identity of the Beneficial Owners, the percentage of the 
Shares to be redeemed (the "Redemption Shares") and the date on which the 
redemption is requested to occur.  The Company agrees that such notice shall 
constitute notice from the holders of the Shares under Section 3(b)(i) of the 
Certificate of Determination.  The Company shall deliver the Shareholder 
Redemption Notice (as defined in the Certificate of Determination) to the 
Trustee and to each Person set forth in Section 22 hereof at least twenty 
(20) but not more than thirty (30) days prior to the Shareholder Redemption 
Date (as defined in the Certificate of Determination). At least ten (10) days 
prior to the Shareholder Redemption Date, each Beneficial Owner shall deliver 
to the Trustee the original Voting Trust Certificate(s) representing the 
Shares Beneficially Owned by such Person along with written instructions to 
the Trustee to either (i) convert the Shares to be redeemed under Section 
1(e) of this Agreement or (ii) to surrender such Shares for redemption.  The 
Trustee shall, (i) at least  three (3) days prior to the Shareholder 
Redemption Date, deliver the certificate(s) representing the Redemption 
Shares as set forth in the Shareholder Redemption Notice (and which have not 
previously been converted) to the Company (or its designated transfer agent) 
and (ii) as soon as practicable thereafter, issue and deliver to such 
Beneficial Owner a Voting Trust Certificate representing the balance of the 
Shares not to be redeemed, if any, represented by the Voting Trust 
Certificate(s) delivered by the Beneficial Owner to the Trustee pursuant to 
this Section 1(g).  Upon the Trustee's receipt of the Series AA Redemption 
Price (as defined in the Certificate of Determination) payable with respect 
to such Redemption Shares, the Trustee shall, as soon as practicable 
thereafter, deliver the Series AA Redemption Price payable with respect to 
such Redemption Shares to the appropriate Beneficial Owner.  Upon Trustee's 
delivery of the Series AA Redemption Price payable with respect to such 
Redemption Shares to the appropriate Beneficial Owner, the Trustee shall be 
fully acquitted and discharged with respect to such Redemption Shares.

          2.   TRUSTEE'S POWERS AND DUTIES.  (a)  During the term of this 
Agreement, the Trustee shall have the exclusive right to vote all Shares 
Beneficially Owned (as defined herein) by a Party on all matters as to which 
such Party is entitled to vote at a meeting of the shareholders of the 
Company, or otherwise, or to which such Party is entitled to express consent 

                                       3

<PAGE>

or dissent to corporate action in writing without a meeting.  The Trustee 
shall give each Party not less than five (5) business days prior written 
notice of any such vote or right to express consent or dissent.  The Trustee 
shall exercise such voting rights, solely as follows: 

                    (i)   With respect to any consolidation, reorganization 
or merger of the Company with or into any other corporation or corporations 
or a sale, conveyance, or other disposition of all or substantially all of 
the Company's property or business (each a "Business Combination") or any 
other transaction or proposal that requires the majority vote of each 
outstanding class of capital stock voting as separate classes and in each 
case would not have an Adverse Effect on the Shares (as defined below), the 
Trustee shall vote the Shares at a regular or special meeting of shareholders 
(or by written consent) proportionately in accordance with the votes cast by 
all holders of the Company's Common Stock for and against such transaction or 
proposal.  If the transaction or proposal would have an Adverse Effect on the 
Shares, the Trustee shall vote the Shares in accordance with Section 2(a)(ii) 
below.

                    (ii)  For all other votes, consents or dissents by 
holders of Shares and for votes that would have an Adverse Effect on the 
Shares, the Trustee shall vote the Shares as follows: 

                          (A)  as directed in writing by the Beneficial Owner 
of such Shares;

                          (B)  if not so directed in writing, proportionately 
in accordance with the votes cast by such Beneficial Owner (or its 
affiliates) with respect to other shares of the Company's stock owned by such 
Beneficial Owner (or its affiliates); or 

                          (C)  if not so directed in writing and if such 
Beneficial Owner does not own or vote any other shares of the Company's stock 
on such matter, the Trustee shall not vote such shares and such shares shall 
not be counted for the purpose of determining whether a quorum is present or 
any percentage of shares of the Company's capital stock is achieved.

               (b)  For purposes of Section 2(a), "Adverse Effect on the 
Shares" shall mean:

                     (i)   any Business Combination in which the Beneficial 
Owners of Shares would not receive as consideration for such Shares (A) cash 
or securities with a fair market value equal to or greater than the then 
applicable Series AA Liquidation Preference (as defined in the Certificate of 
Determination of Series AA Preferred Stock) with respect to such Shares, and 
(B) if the form of such consideration is other than cash, publicly-traded 
equity securities of securities convertible into publicly-traded equity 
securities, securities having rights, preferences, privileges or restrictions 
at least equivalent to those of the Shares; or

                    (ii)   any other proposal or transaction that would:

                                       4

<PAGE>

                          (A)  Increase or decrease the aggregate number of 
authorized shares of the Series AA Preferred Stock, other than an increase as 
provided in either subdivision (b) of Section 405 or subdivision (c) of 
Section 902 of the California Corporation Code;

                          (B)  Effect an exchange, reclassification, or 
cancellation of all or part of the shares of Series AA Preferred Stock, 
including a reverse stock split but excluding a stock split;

                          (C)  Effect an exchange, or create a right of 
exchange, of all or part of the shares of another class of capital stock into 
shares of the Series AA Preferred Stock;

                          (D)  Change the rights, preferences, privileges or 
restrictions of the Shares, other than as a result of the creation of a new 
series of Preferred Stock;

                          (E)  Create a new class of shares having rights, 
preferences or privileges prior to the Shares, or increase the rights, 
preferences or privileges or the number of authorized shares of any class 
having rights, preferences or privileges prior to the Shares;

                          (F)  Reclassify the Shares into series having 
different rights, preferences, privileges or restrictions, or authorize the 
Board to do so; or 

                          (G)  Cancel or otherwise affect dividends on the 
Shares which have accrued but have not been paid.

               (c)   Except as expressly granted under Section 2(a)(i) above 
with respect to the voting rights enumerated therein, the Trustee shall have 
no rights with respect to the Shares.  Without limiting the preceding 
sentence, the parties acknowledge that the Trustee shall have no authority to 
sell, encumber or otherwise dispose of any Shares.  The Trustee shall have no 
voting or other rights with respect to any shares of capital stock 
Beneficially Owned as of the date hereof by any Party other than the Shares.

          3.   TRANSFER.  The provisions of this Agreement shall be binding 
upon the successors in interest to any of the Shares.  The Company shall not 
permit the transfer of any of the Shares on their books or issue new 
certificates representing the Shares or any new Voting Trust Certificates 
unless and until the person to whom such units are to be transferred shall 
have executed a written agreement, substantially in the form of this 
Agreement, pursuant to which such person becomes a party to this Agreement.  
Nothing in the foregoing sentence shall, however, invalidate any succession 
in ownership occurring by operation of law, and any successor by operation of 
law shall be bound by this Agreement as fully and completely as if the 
successor were a party to this Agreement.

          4.   NO WITHDRAWAL.  No Party may withdraw from this Agreement 
prior to termination of this Agreement pursuant to Section 7 hereof.

                                       5

<PAGE>

          5.   REPLACEMENT OR REMOVAL OF TRUSTEE.  In the event of the 
Trustee's dissolution, resignation, removal or inability to act, the Parties 
shall select a successor or Trustee mutually acceptable to the Company and 
the holders of a majority of the Shares Beneficially Owned then outstanding.  
Any Trustee may be removed by the affirmative vote of a majority of the 
Shares then outstanding or the Company.  Notwithstanding any change in the 
Trustee, the certificates for Shares standing in the name of the Trustee may 
be endorsed and transferred to any successor Trustee without the further 
action of any Party or predecessor Trustee with the same effect as if 
endorsed and transferred by the Trustee who has ceased to act.

          6.   TRUSTEE'S LIABILITY AND INDEMNITY.  The Trustee shall not be 
liable for any error of judgment or mistake of fact or law, or for any act or 
omission undertaken in good faith in connection with the Trustee's powers and 
duties under this Agreement, except for the Trustee's own willful misconduct 
or gross negligence.  The Trustee is authorized and empowered to construe 
this Agreement and its reasonable construction made in good faith shall be 
conclusive and binding upon the Company and the Parties.  The Trustee shall 
not be liable for acting on any legal advice or on any notice, request or 
instruction or other document believed by the Trustee to be genuine and to 
have been signed by the proper Party or Parties.  The Company shall indemnify 
the Trustee for, and hold the Trustee harmless against, any expenses, claims, 
losses, damages or liabilities, including without limitation attorneys' fees, 
incurred by the Trustee and arising out of or in connection with the 
administration of this trust and its rights and duties hereunder, except to 
the extent that a court of competent jurisdiction determines that the Trustee 
is not entitled to such indemnification because the action giving rise to 
such indemnification was the result of willful misconduct or gross negligence 
by the Trustee.  This indemnity shall survive the termination of this 
Agreement.

          7.   TERM.  This Agreement shall terminate and be of no further 
force or effect on the earlier of (a) the closing of the acquisition of the 
Company by another entity by means of any transaction or series of related 
transactions (including, without limitation, any reorganization, merger or 
consolidation) that results in the transfer of fifty percent (50%) or more of 
the outstanding voting power of the Company or a sale of all or substantially 
all of the assets of the Company, (b) such time as no Shares are outstanding, 
or (c) ten (10) years from the date hereof.

     At any time within two (2) years prior to the time of expiration of this 
Agreement pursuant to Section 7(c), the Company and the Parties may, by 
written agreement and with the written consent of the Trustee, extend the 
duration of this Agreement for an additional period not exceeding ten (10) 
years from the expiration date of this Agreement as originally fixed or as 
last extended as provided in this paragraph.

     As soon as practicable after the termination of this Agreement, the 
Trustee shall deliver to each Party share certificates or securities 
representing the number of Shares or other securities in respect of which 
Voting Trust Certificates registered in the name of such Party are then 
outstanding, upon the surrender of such Voting Trust Certificates properly 
endorsed and upon payment by the persons entitled to receive such share 
certificates or other securities of a sum sufficient to cover any tax or 
governmental charge in respect of the transfer or delivery of such 
certificates.  If any Party cannot be located or fails or refuses to 
surrender Voting Trust 

                                       6

<PAGE>

Certificates in exchange for Shares or other securities as aforesaid, the 
Trustee shall deliver said Shares or other securities to the Company or to 
any bank or trust company in California for the benefit of the Person or 
Persons entitled thereto.  Upon any such delivery, the Trustee shall be fully 
acquitted and discharged with respect to said Shares or other securities.

          8.   COVENANTS OF THE COMPANY.  The Company agrees to use its best 
efforts to ensure that the rights granted hereunder are effective and that 
the Parties hereto enjoy the benefits thereof.  The Company will not, by any 
voluntary action, avoid or seek to avoid the observance or performance of any 
of the terms to be performed hereunder by the Company, but will at all times 
in good faith assist in the carrying out of all of the provisions of this 
Agreement and in the taking of all such actions as may be necessary, 
appropriate or reasonably requested by the holders of a majority of the 
outstanding Shares in order to protect the rights of the Parties hereunder 
against impairment.

          9.   DEFINED TERMS.  As used in this Agreement, the following terms 
have the respective meanings set forth below: 

          BENEFICIAL OWNER:  shall have the meaning set forth in Rule 
13d-3(a) and (b) of the Rules and Regulations to the Securities Exchange Act 
of 1934, as amended; and Beneficially Owned shall have a correlative meaning.

          PERSON:  shall mean an individual, partnership, corporation, trust, 
limited liability company or unincorporated organization, and a government or 
agency or political subdivision thereof.

          SHARES:  shall consist of all shares of Series AA Preferred Stock 
issued to GWA pursuant to the Securities Purchase Agreement or thereafter 
obtained by a Party.

          10.  REMEDIES.  The Company and the Parties agree and acknowledge 
that money damages may not be an adequate remedy for breach of the provisions 
of this Agreement and that the Company and any Party shall be entitled, in 
its sole discretion, to apply to any court of competent jurisdiction for 
specific performance, injunctive relief or such other equitable remedy or 
remedies as the court may in its discretion order to enforce or prevent any 
violations of the provisions of this Agreement, in addition to its remedies 
at law.  In respect of any such equitable remedy so sought, the Company and 
the Parties hereby waive the requirement of the posting of any bond or the 
necessity to show irreparable injury on the part of the Person seeking such 
relief.

          11.  NOTICES.  Unless otherwise provided, any notice required or 
permitted under this Agreement shall be given in writing and shall be deemed 
effectively given upon delivery by confirmed facsimile or reliable 
international courier service or upon personal delivery to the party to be 
notified.

          12.  MODIFICATION, AMENDMENT, WAIVER.  Any term hereof may be 
amended and the observance of any term hereof may be waived (either generally 
or in a particular instance and either retroactively or prospectively) only 
with the written consent of the holders of a 

                                       7

<PAGE>

majority of the then outstanding voting Shares Beneficially Owned by the 
Party or Parties for whose benefit such term has been included and the 
Company; provided that, the Trustee must consent in writing to any amendment 
or modification that changes the rights, obligations and/or liability of the 
Trustee under this Agreement.  Any amendment or waiver so effected shall be 
binding upon the Parties hereto.  The failure of the Trustee, the Company or 
any Party at any time to enforce any of the provisions of this Agreement 
shall in no way be construed as a waiver of such provisions and shall not 
affect the rights of the Trustee, the Company or any Party thereafter to 
enforce the provisions of this Agreement in accordance with its terms.

          13.  COMPLETE AGREEMENT.  This document, the Voting Trust 
Certificates, the Securities Purchase Agreement and the Amended and Restated 
Articles of Incorporation (including the Certificate of Determination 
thereto) of the Company embody the complete agreement and understanding 
between and among the Parties hereto with respect to the subject matter 
hereof, and supersede and preempt any prior understandings, agreements or 
representations by or among the parties hereto, written or oral, which may 
have related to the subject matter hereof.

          14.  SUCCESSORS AND ASSIGNS.  This Agreement will bind and inure to 
the benefit of and be enforceable by the Parties and their respective 
permitted transferees, successors and assigns.

          15.  LEGENDS.  

               (a)  In addition to legends required by the Securities 
Purchase Agreement, each certificate evidencing Shares shall bear a legend in 
substantially the following form:

     THE SHARES REPRESENTED BY THIS CERTIFICATE ARE SUBJECT TO RESTRICTIONS
     ON VOTING AND TRANSFER AS SET FORTH IN THE VOTING TRUST AGREEMENT, DATED
     ON OR ABOUT APRIL 1998, A COPY OF WHICH IS AVAILABLE FROM THE COMPANY
     AND ANY SUCCESSOR THERETO.

               (b)  Each Voting Trust Certificate evidencing Shares shall 
bear a legend in substantially the following form:

     THE SECURITIES REPRESENTED BY THIS CERTIFICATE HAVE NOT BEEN REGISTERED
     UNDER THE SECURITIES ACT OF 1933, AS AMENDED, AND MAY NOT BE SOLD,
     TRANSFERRED OR ASSIGNED, PLEDGED OR HYPOTHECATED ABSENT AN EFFECTIVE
     REGISTRATION THEREOF UNDER SUCH ACT OR COMPLIANCE WITH RULE 144
     PROMULGATED UNDER SUCH ACT, OR UNLESS THE COMPANY HAS RECEIVED AN
     OPINION OF COUNSEL TO THE HOLDER HEREOF (WHICH COUNSEL SHALL BE
     REASONABLY SATISFACTORY TO THE COMPANY) THAT SUCH REGISTRATION IS NOT
     REQUIRED.

                                       8

<PAGE>

     THE SHARES REPRESENTED BY THIS CERTIFICATE ARE SUBJECT TO RESTRICTIONS
     ON VOTING AND TRANSFER AS SET FORTH IN THE VOTING TRUST AGREEMENT, DATED
     AS OF MARCH __, 1998, A COPY OF WHICH IS AVAILABLE FROM THE COMPANY AND
     ANY SUCCESSOR THERETO.

          16.  COUNTERPARTS.  This Agreement may be executed in separate 
counterparts, each of which will be an original and all of which taken 
together will constitute one and the same Agreement.

          17.  APPLICABLE LAW.  All questions concerning this Agreement will 
be governed by and interpreted in accordance with the internal laws of the 
State of California, without regard to internal law concerning choice or 
conflict of law. Any disputes arising hereunder shall be resolved before the 
appropriate state or federal courts in the State of California, and the 
Parties hereto hereby consent to the personal jurisdiction of such courts in 
respect of such disputes.

          18.  SEVERABILITY.  If any one or more of the provisions of this 
Agreement, as applied to the Trustee, the Company or any Party or any 
circumstance, shall, for any reason, be held to be invalid, illegal or 
unenforceable in any respect, such invalidity, illegality or unenforceability 
shall not affect any other provisions of this Agreement, and this Agreement 
shall be construed as if such invalid, illegal or unenforceable provision had 
never been contained herein.  If any one or more of the provisions of this 
Agreement shall, for any reason, be held to be unenforceable as to duration, 
scope, activity or subject, such provisions shall be construed by limiting 
and reducing it so as to make such provision enforceable to the extent 
compatible with the then existing applicable law.

          19.  TRUSTEE'S EXPENSES.  The Trustee shall be reimbursed by the 
Company for its initial and annual fees pursuant to the fee letter dated as 
of March 5, 1998, and all reasonable out-of-pocket expenses (including its 
reasonable attorneys' fees) incurred pursuant to this Agreement.

          20.  NATURE OF RELATIONSHIP.  The Trust created by this Agreement 
is not intended to be, shall not be deemed to be and shall not be treated as 
a general partnership, limited partnership, joint venture, corporation, joint 
stock company or association.  The relationship of the Parties to the Trustee 
shall be solely that of beneficiaries of the Trust created by this Agreement, 
and their rights and obligations shall be limited to those set forth in this 
Agreement.

          21.  INVESTMENT REPRESENTATIONS.  In acquiring Voting Trust 
Certificates hereunder, each Party acknowledges and represents that such 
Party has had an opportunity to discuss the business of the Company with the 
officers and directors of the Company and has received satisfactory answers 
in response to such inquiries. Such Party further acknowledges that the 
Voting Trust Certificates are highly speculative and involve a high degree of 
risk and that the Voting Trust Certificates have not been registered under 
the Securities Act of 1933, as amended (the "Act") and may not be sold or 
otherwise disposed of except pursuant to an exemption from the Act.  Such 
Party represents and warrants to the Trustee and the Company 

                                       9

<PAGE>

that such Party is acquiring the Voting Trust Certificate for such Party's 
own account for investment and not with a view to or for sale in connection 
with any distribution of said Voting Trust Certificates or with any present 
intention of distributing or selling said Voting Trust Certificates, and such 
Party does not presently have reason to anticipate any change in 
circumstances or any particular occasion or event that would cause it to sell 
said Voting Trust Certificate.

          22.  NOTICES.  All notices, demands and other communications made 
hereunder shall be in writing and shall be given either by personal delivery, 
by nationally recognized overnight courier (with charges prepaid) or by 
facsimile (with telephone confirmation), and shall be deemed to have been 
given or made when personally delivered, the day following the date deposited 
with such overnight courier service or when transmitted to telecopy machine 
and confirmed by telephone, addressed to the respective parties at the 
following addresses (or such other address for a party as shall be specified 
by like notice):

          If to the Company:

               Affymetrix, Inc.
               3380 Central Expressway
               Santa Clara, California  95051
               Attention: Edward Hurwitz, Chief Financial Officer
               Telephone:  408-731-5000
               Facsimile:  408-481-0422

          With a copy (which shall not constitute notice) to:

               Gunderson Dettmer Stough Villeneuve Franklin & Hachigian, LLP
               155 Constitution Drive
               Menlo Park, California  94025
               Attention:  Carla S. Newell
               Telephone:     650-463-5470
               Facsimile:     650-321-2800

          If to the Beneficial Owner:
               Glaxo Wellcome Inc.

               Five Moore Drive
               Research Triangle Park, North Carolina  27709
               Attention:  General Counsel
               Telephone:     919-483-2505
               Facsimile:     919-483-0265
               
          If to the Trustee:

               Wachovia Bank, N.A.
               100 Main Street

                                      10

<PAGE>

               Winston-Salem, North Carolina  27102
               Attention:  John N. Smith, III, Executive Services Department
               Telephone:     336-770-6984
               Facsimile:     336-770-4059
               
          23.  INSPECTION.  A duplicate of this Agreement and any extension 
hereof shall be filed with the Trustee and shall be open to inspection by any 
shareholder of the Company, any holder of a Voting Trust Certificate or the 
agent of either, upon the same terms as the record of shareholders of the 
Company is open to inspection.

                                      11

<PAGE>

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

                                             COMPANY:


                                             AFFYMETRIX, INC.


                                             By: 
                                                -------------------------------
                                             Print Name:
                                                        -----------------------
                                             Title:
                                                   ----------------------------

                                             Address:  3380 Central Expressway
                                                       Santa Clara, CA  95051


                                             TRUSTEE:
                                        
                                        
                                             WACHOVIA BANK, N.A.
                                        
                                        
                                             By: 
                                                -------------------------------
                                             Print Name:
                                                        -----------------------
                                             Title:
                                                   ----------------------------

                                             Address:  100 Main Street
                                                       Winston-Salem, NC  27102
                                        

                                             GWA:


                                             GLAXO WELLCOME AMERICAS INC.


                                             By: 
                                                -------------------------------
                                             Print Name:
                                                        -----------------------
                                             Title:
                                                   ----------------------------

                                             Address:  499 Park Avenue
                                                       New York, NY  10022

<PAGE>

                                  SCHEDULE I

     THE SECURITIES REPRESENTED BY THIS CERTIFICATE HAVE NOT BEEN REGISTERED
     UNDER THE SECURITIES ACT OF 1933, AS AMENDED, AND MAY NOT BE SOLD,
     TRANSFERRED OR ASSIGNED, PLEDGED OR HYPOTHECATED ABSENT AN EFFECTIVE
     REGISTRATION THEREOF UNDER SUCH ACT OR COMPLIANCE WITH RULE 144
     PROMULGATED UNDER SUCH ACT, OR UNLESS THE COMPANY HAS RECEIVED AN
     OPINION OF COUNSEL TO THE HOLDER HEREOF (WHICH COUNSEL SHALL BE
     REASONABLY SATISFACTORY TO THE COMPANY) THAT SUCH REGISTRATION IS NOT
     REQUIRED.

     THE SHARES REPRESENTED BY THIS CERTIFICATE ARE SUBJECT TO RESTRICTIONS
     ON VOTING AND TRANSFER AS SET FORTH IN THE VOTING TRUST AGREEMENT, DATED
     AS OF MARCH __, 1998, A COPY OF WHICH IS AVAILABLE FROM THE COMPANY AND
     ANY SUCCESSOR THERETO.

               This certifies that Glaxo Wellcome Americas Inc. has deposited 
or has caused to be deposited 1,634,522 shares of the Series AA Preferred 
Stock of Affymetrix, Inc., a California corporation (the "Company"), under a 
Voting Trust Agreement, dated as of March __, 1998 (the "Voting Trust 
Agreement"), among the Company, Wachovia Bank, N.A. (the "Trustee"), and the 
Parties named in the Voting Trust Agreement.  The Trustee shall possess and 
be entitled to the exclusive right to vote such shares upon the terms and 
subject to the conditions stated in the Voting Trust Agreement.

               This Voting Trust Certificate shall be transferable only on 
the records of the Trustee upon surrender hereof by the registered holder in 
person or by attorney duly authorized and, until so transferred, the Trustee 
may treat the registered holder as the owner of this Voting Trust Certificate 
for all purposes whatsoever, unaffected by any notice to the contrary.  As a 
condition precedent to the making of any transfer of this Voting Trust 
Certificate, the Trustee may require the payment of a sum sufficient to cover 
the amount of any taxes or other governmental charges incident thereto.

               This Voting Trust Certificate is issued pursuant to, and the 
rights of the holder hereof are subject to and limited by the terms and 
conditions of, the Voting Trust Agreement.  The holder of this Voting Trust 
Certificate, by the acceptance hereof, assents to and agrees to be bound by 
all the terms and conditions of the Voting Trust Agreement.  Copies of the 
Voting Trust Agreement are on file at the principal office of the Company and 
at the office of the Trustee.

               Certificates for the number of shares in respect of which this 
Voting Trust Certificate was issued, or the net proceeds in cash or property 
of said number of shares at the 

<PAGE>

time of surrender hereof, all as provided in the Voting Trust Agreement, 
shall be deliverable hereunder upon the termination of the Voting Trust 
Agreement.

Dated: ____________, 199_

                                        WACHOVIA BANK, N.A.,
                                        as Trustee
          
          
                                        By:
                                           -------------------------------------
          
                                         Its:
                                            ------------------------------------

<PAGE>

                                                        EXHIBIT C OF EXHIBIT 10

                      AMENDMENT TO GOVERNANCE AGREEMENT

               THIS AMENDMENT TO GOVERNANCE AGREEMENT ("Amendment") is 
entered into as of March __, 1998, by and between Affymetrix, Inc. (the 
"Company") and Glaxo Wellcome PLC ("Glaxo Wellcome").  Capitalized terms not 
otherwise defined in this Amendment have the meaning given them in that 
certain Governance Agreement (the "Governance Agreement") dated as of July 6, 
1995, by and between Affymetrix, Inc. and Glaxo Wellcome.

                                   RECITALS
                                          
               A.   The Company and Glaxo Wellcome constitute all of the 
parties to the Governance Agreement and desire to enter into this Amendment.

               B.   The Company and Glaxo Wellcome Americas Inc. ("GWA"), a 
wholly owned subsidiary of Glaxo Wellcome, are entering into that certain 
Series AA Preferred Stock Purchase Agreement ("Purchase Agreement") of even 
date herewith pursuant to which GWA is purchasing shares of the Company's 
Series AA Preferred Stock.

               C.   In order to induce the Company to enter into the Purchase 
Agreement and to induce GWA to invest funds in the Company pursuant to the 
Purchase Agreement, the Company and Glaxo Wellcome desire to make the 
amendments described herein to the Governance Agreement.

               NOW, THEREFORE, in consideration of the mutual promises and 
covenants described below, the Company and Glaxo Wellcome hereby agree as 
follows:

           1.  Paragraph 1 of the Governance Agreement shall be amended and 
restated to read in full as follows:

                "So long as GLAXO WELLCOME or any of its subsidiaries, 
     including, but not limited to, Glaxo Wellcome Americas Inc., 
     (collectively, "GW") together own, or are part of a group that owns, 
     (a) a majority of the outstanding AFFYMETRIX voting shares, GW (or such 
     group) will have the right to designate five out of nine AFFYMETRIX 
     directors, (b) less than a majority but greater than 35% of the 
     outstanding AFFYMETRIX voting shares, GW (or such group) will have the 
     right to designate four out of nine AFFYMETRIX directors, (c) less than 
     a 35% but greater than 25% of the outstanding AFFMETRIX voting shares, 
     GW (or such group) will have the right to designate three out of nine 
     AFFYMETRIX directors, (d) less than 25% but more than 15% of the 
     outstanding AFFYMETRIX voting shares, GW (or such group) will have the 
     right to designate two out of nine AFFYMETRIX directors and (e) less 
     than 15% but more than 5% of the outstanding AFFYMETRIX voting shares, 
     GW (or such group) will have the right to designate one out of nine 
     AFFYMETRIX directors, in each case such designations to be included as 
     part of the management slate to be recommended to the shareholders 
     subsequent to 1995. For purposes of determining the percentage of 
     outstanding voting 

<PAGE>

     shares held by GW (or such group), shares of Series AA Preferred Stock 
     held by GW shall not be counted; PROVIDED HOWEVER, that upon conversion 
     of the shares of Series AA Preferred Stock owned by GW into shares of 
     Common Stock, such shares of Common Stock shall be counted for purposes 
     of determining the percentage of outstanding voting shares held by GW 
     (or such group). All discretionary proxies will be voted in favor of 
     such nominees. GW (or such group) will otherwise vote its shares, or 
     give its proxy to vote its shares, for the other nominees on the slate 
     of directors recommended to the shareholders. The parties agree to take 
     appropriate action, if necessary, to comply with the requirements of the 
     California Corporations Code to make this provision valid and 
     enforceable, including without limitation, to enter into a voting trust 
     agreement."

               2.   The last sentence of paragraph 6.2(a) of the Governance 
Agreement is hereby amended and restated to read in its entirety as follows:  

     "'Registrable Securities' shall mean all Common Stock of the Company 
     issued or issuable upon conversion of the Company's Series 1 Subordinated
     Convertible Preferred Stock, Series 2 Convertible Preferred Stock and
     Series AA Preferred Stock, including Common Stock issued pursuant to stock
     splits, stock dividends and similar distributions with respect to such
     shares."

               3.   The terms and conditions of this Amendment and the 
Governance Agreement shall inure to the benefit of and be binding upon the 
respective successors and assigns of the parties.

               4.   This Amendment may be executed in two or more 
counterparts, each which shall be deemed to be an original, but all of which 
together shall constitute one and the same instrument.

               5.   This Amendment shall be governed by and construed under 
the laws of the State of California as applied to agreements entered into 
solely between residents of and to be performed entirely within such state.

               6.   The Governance Agreement and this Amendment constitute 
the entire agreement between the parties hereto pertaining to the subject 
matter thereof and hereof.

                                       2

<PAGE>

               IN WITNESS WHEREOF, the undersigned have executed this 
Amendment to Governance Agreement as of the day and year first above written.

AFFYMETRIX, INC.                         GLAXO WELLCOME PLC


By:                                      By:
   ------------------------------           ------------------------------
Title:                                   Title:
      ---------------------------               --------------------------


AGREED TO AND ACCEPTED BY:

GLAXO WELLCOME AMERICAS INC.



By:
   ------------------------------
Title:
      ---------------------------

                                       3


<PAGE>

                                                                     EXHIBIT 99

                  TEXT OF PRESS RELEASE DATED MARCH 10, 1998


FOR IMMEDIATE RELEASE

Affymetrix Announces Definitive Agreement to Sell $50 Million of Series AA 
Preferred Stock 

March 10, 1998 8:00 AM EST

SANTA CLARA, Calif., March 10 /PRNewswire/ -- Affymetrix, Inc., (Nasdaq: 
AFFX) announced today that it has entered into a definitive agreement with 
Glaxo Wellcome Americas, Inc., to sell 1,634,522 shares of Series AA 
Preferred Stock for an aggregate purchase price of $50 million. The 
transaction, which is subject to customary closing conditions including 
regulatory approval, is expected to close in approximately 30 days. The 
Series AA Preferred Stock will be convertible into Affymetrix Common Stock at 
approximately $40 per share. Until such time as the Series AA Preferred 
Shares are converted into Common Stock, Affymetrix will pay a 6 1/2% dividend 
on such Shares. 

The Company intends to use the proceeds from the sale of the Series AA 
Preferred Shares for capital expenditures (manufacturing scale-up and 
construction of a new manufacturing facility, expansion of research and 
development facilities), research and development, expansion of sales and 
marketing, working capital and other general corporate purposes. 

The Series AA Preferred Shares and the Common Stock underlying the Series AA 
Preferred Shares have not been registered under the Securities Act of 1933. 
Accordingly, the Series AA Preferred Shares and the underlying common stock 
may not be offered or sold in the United States, except pursuant to an 
applicable exemption from the registration requirements of the Securities 
Act. 

This press release shall not constitute an offer to sell or the solicitation 
of an offer to buy the Series AA Preferred Shares. This press release is 
being issued pursuant to and in accordance with rule 135c under the 
Securities Act. SOURCE Affymetrix, Inc. 




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