STOCK PURCHASE AGREEMENT


         THIS STOCK PURCHASE AGREEMENT is made by and between LYNX THERAPEUTICS,
INC.,   a  Delaware   corporation   (the   "Company"),   and  Edward  C.  Albini
("Purchaser").

                                   WITNESSETH:

         WHEREAS,  Purchaser holds one stock option to purchase shares of common
stock of the  Company  pursuant  to the  Company's  1992 Stock  Option Plan (the
"Plan") which Purchaser desires to exercise;

         WHEREAS,  Purchaser  wishes to take  advantage  of the  early  exercise
provision of his options; and

         NOW, THEREFORE, IT IS AGREED between the parties as follows:

         1.  Purchaser  hereby  agrees to  purchase  from the  Company,  and the
Company  hereby  agrees to sell to  Purchaser,  an aggregate  of fifty  thousand
(50,000)  shares of the Company's  common stock (the  "Stock"),  for an exercise
price of ($5.00) per share (total  exercise  price:  two hundred fifty  thousand
dollars ($250,000), payable as follows:

                   Cash at Closing                    $    -0-

                   Promissory Note in the form
                   of Exhibit E (the "Note")          $250,000

                   Total Exercise Price                    $250,000

         The closing  hereunder shall occur at the offices of the Company on the
date of this  Agreement  or at such  other  time and  place as the  parties  may
mutually agree upon in writing.

         At the closing, Purchaser shall deliver one (1) stock assignment in the
form of Exhibit B, duly  endorsed  (with date and number of shares left  blank),
joint  escrow  instructions  (the "Joint  Escrow  Instructions")  in the form of
Exhibit C, duly executed by Purchaser,  and the total exercise price  (including
an  executed  Note in the form of Exhibit E if a portion  of the total  exercise
price is to be paid by promissory note and an executed  pledge  agreement in the
form of Exhibit F (the "Pledge  Agreement")  under which all shares of the Stock
acquired by Note shall be pledged as collateral  security for the payment of the
indebtedness represented by the Note).

         At the closing or as soon thereafter as practicable,  the Company shall
deliver to the Escrow Agent (as defined in paragraph 8 below) share certificates
for all of the Stock that is to be subject to the Purchase Option (as defined in
paragraph 2 below), and shall deliver share certificates to Purchaser for all of
the  Stock,  if any,  that is not to be subject  to the  Purchase  Option or the
Pledge  Agreement.  The certificates for all of the Stock that is subject to the
Pledge Agreement but not the Purchase Option shall be retained by the Company as
security pursuant to the Pledge Agreement.

         2.  In  accordance  with  the  provisions  of  Section  408(b)  of  the
California General  Corporation Law, fifty thousand (50,000) shares of the Stock
to be purchased by Purchaser  pursuant to this  Agreement with an exercise price
of five  dollars  ($5.00)  per share  shall be subject to the  following  option
("Purchase Option"):

                  (a) Subject to the  provisions of Exhibit A, in the event that
Purchaser shall cease to be an employee of the Company for any reason (including
his death),  or no reason,  with or without  cause,  the Purchase  Option may be
exercised.  The Company  shall have the right at any time within the ninety (90)
day period  after  Purchaser's  termination  of service with the Company and all
related  companies or such longer  period as may be agreed to by the Company and
Purchaser (for example,  for purposes of satisfying the  requirements of Section
1202(c)(3)  of the  Internal  Revenue  Code) to purchase  from  Purchaser or his
personal  representative,  as the case may

                                      57.
<PAGE>

be, at the price per share paid by Purchaser pursuant to this Agreement ("Option
Price"),  up to but not exceeding the number of shares of the Stock set forth on
Exhibit A hereto which is incorporated herein by this reference.

                  (b) In addition,  and without limiting the foregoing  Purchase
Option, if at any time during the term of the Purchase Option, there occurs: (a)
a  dissolution  or  liquidation  of the Company;  (b) a merger or  consolidation
involving the Company in which the Company is not the surviving corporation; (c)
a reverse  merger in which the  Company  is the  surviving  corporation  but the
shares of the  Company's  common stock  outstanding  immediately  preceding  the
merger are converted by virtue of the merger into other property, whether in the
form  of  other  securities,  cash  or  otherwise;  or  (d)  any  other  capital
reorganization  in which  more than  fifty  percent  (50%) of the  shares of the
Company  entitled to vote are  exchanged,  then: (i) if there is no successor to
the Company, the Company shall have the right to exercise its Purchase Option as
to all or any portion of the Stock then subject to the Purchase Option set forth
above to the same extent as if Purchaser's  employment by the Company had ceased
on the date preceding the date of consummation of said event or transaction,  or
(ii) the Purchase  Option may be assigned to any  successor of the Company,  and
the Purchase Option shall apply if Purchaser shall cease for any reason to be an
employee of such  successor on the same basis as set forth above.  In that case,
references herein to the "Company" shall be deemed to refer to such successor.

                  (c) The  Company  shall  be  entitled  to pay  for any  shares
purchased  pursuant to its Purchase  Option at the Company's  option in cash, by
offset against any indebtedness given in payment for the Stock, or a combination
of both.

                  (d) As used herein,  employment with the Company shall include
employment with an affiliate of the Company.

                  (e) This  Agreement is not an employment  contract and nothing
in this Agreement shall be deemed to create in any way whatsoever any obligation
on the part of  Purchaser  to continue in the employ of the  Company,  or of the
Company to continue Purchaser in the employ of the Company.

                  (f) In the  event  that the  Stock's  Fair  Market  Value  (as
defined  in the Plan) is equal to or exceeds  the Option  Price on the date that
the Purchaser  ceases to be employed,  the Company  shall  exercise its Purchase
Option to the extent permitted by law.

         3. The Purchase  Option may be exercised  by giving  written  notice of
exercise delivered or mailed as provided in paragraph 14. Upon providing of such
notice and payment or tender of the purchase price, the Company shall become the
legal and  beneficial  owner of the Stock  being  purchased  and all  rights and
interests therein or related thereto.

         4. If from time to time during the term of the Purchase Option there is
any stock  dividend  or  liquidating  dividend  or  distribution  of cash and/or
property,  stock split or other change in the  character or amount of any of the
outstanding  securities of the Company,  then,  in such event,  any and all new,
substituted  or additional  securities or other  property to which  Purchaser is
entitled by reason of his ownership of Stock will be immediately  subject to the
Purchase  Option and be  included in the word  "Stock"  for all  purposes of the
Purchase  Option  with the same  force and  effect as the  shares of Stock  then
subject to the  Purchase  Option.  While the total Option Price shall remain the
same after each such event, the Option Price per share of Stock upon exercise of
the Purchase Option shall be appropriately adjusted.

         5. All  certificates  representing  any shares of Stock of the  Company
subject to the provisions of this Agreement shall have endorsed  thereon legends
in substantially the following form:

                  (i) "The shares represented by this certificate are subject to
an option set forth in an agreement  between the  corporation and the registered
holder,  or his  predecessor  in  interest,  a copy of  which  is on file at the
principal office of this corporation.  Any transfer or attempted transfer of any
shares subject to such option is void without the prior express  written consent
of the issuer of these shares."

                                      58.
<PAGE>

                   (ii)  Any  legend  required  to  be  placed  thereon  by  the
California Commissioner of Corporations.

         6. As  security  for his  faithful  performance  of the  terms  of this
Agreement and to insure the availability for delivery of Purchaser's  Stock upon
exercise of the Purchase Option herein provided for,  Purchaser  agrees,  at the
closing  hereunder (or as soon thereafter as  practicable),  to deliver (or have
the Company deliver on the Purchaser's behalf) to and deposit with the Secretary
of the Company ("Escrow Agent"), as Escrow Agent in this transaction,  three (3)
stock  assignments  duly endorsed (with date and number of shares left blank) in
the  form  attached  hereto  as  Exhibit  B,  together  with  a  certificate  or
certificates  evidencing all of the Stock subject to the Purchase  Option;  said
documents  are to be held by the Escrow Agent and delivered by said Escrow Agent
pursuant to the Joint Escrow Instructions of the Company and Purchaser set forth
in Exhibit C attached hereto and  incorporated  herein by this reference,  which
instructions  shall  also  be  delivered  to the  Escrow  Agent  at the  closing
hereunder  (or as soon  thereafter  as  practicable).  If a portion of the total
purchase  price is paid by a promissory  note,  the Stock is also subject to the
Pledge  Agreement,  and possession of the certificates and stock  assignments by
the  Escrow  Agent  shall  also  constitute  possession  by the  Company of such
instruments pursuant to the Pledge Agreement.

         7. Purchaser shall not sell or transfer any of the Stock subject to the
Purchase Option or any interest  therein so long as such Stock is subject to the
Purchase Option or the Pledge Agreement.

         8. The Company  shall not be required  (i) to transfer on its books any
shares of Stock of the  Company  which  shall have been sold or  transferred  in
violation of any of the  provisions set forth in this Agreement or (ii) to treat
as owner of such  shares or to accord  the right to vote as such owner or to pay
dividends to any transferee to whom such shares shall have been so transferred.

         9. Subject to the  provisions  of  paragraphs 7 and 8 above,  Purchaser
(but not any unapproved  transferee)  shall,  during the term of this Agreement,
exercise all rights and  privileges of a stockholder of the Company with respect
to the Stock.

         10. Purchaser  acknowledges  receipt of a copy of Section 260.141.11 of
Title 10 of the California Administrative Code, attached hereto as Exhibit D.

         11. The parties agree to execute such further  instruments  and to take
such further  action as  reasonably  may be necessary to carry out the intent of
this Agreement.

         12.  Any  notice  required  or  permitted  hereunder  shall be given in
writing and shall be deemed  effectively  given upon  personal  delivery or upon
deposit in any United States Post Office Box, by  registered  or certified  mail
with postage and fees prepaid, addressed to the other part hereto at his address
hereinafter  shown below his signature or at such other address as such part may
designate by ten (10) days' advance written notice to the other part hereto.

         13.  This  Agreement  shall  bind  and  inure  to  the  benefit  of the
successors  and  assigns of the  Company  and,  subject to the  restrictions  on
transfer  herein  set  forth,  inure  to the  benefit  of and  be  binding  upon
Purchaser,  his  heirs,  executors,  administrators,  successors,  and  assigns.
Without  limiting the  generality of the foregoing,  the Purchase  Option of the
Company hereunder shall be assignable by the Company at any time or from time to
time,  in whole or in part.  Should the right of  repurchase  be assigned by the
Company, the assignee shall pay to the Company cash equal to the excess, if any,
of the Stock's Fair Market Value (as defined in the Plan) over the Option Price.

         IN WITNESS WHEREOF,  the parties hereto have executed this Agreement as
of the 14th day of April 1997.

                                               LYNX THERAPEUTICS INC.


                                               By Sam Eletr
                                                  -----------------------------
                                                     Sam Eletr

                                      59.
<PAGE>

                                                        Chief Executive Officer
                                            Address:    3832 Bay Center Place
                                                        Hayward, CA 94545

                                                     PURCHASER


                                                     /s/ Edward C. Albini
                                                     --------------------------
                                                     Edward C. Albini

                                            Address:
                                                    ---------------------------


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


         ATTACHMENTS:

         Exhibit A         Vesting Schedule
         Exhibit B         Assignment Separate from Certificate
         Exhibit C         Joint Escrow Instructions
         Exhibit D         Cal. Admin. Code, Title 10, Section 260.141.11
         Exhibit E         Promissory Note
         Exhibit F         Pledge Agreement


                                      60.
<PAGE>

                                    Exhibit A

                                VESTING SCHEDULE



                                                          Number of Shares
                                                          Subject to
         If Cessation of Employment Occurs:               Purchase Option:

         On or before April 13, 1998                      50,000 shares

         On or after April 14, 1998
           but on or before May 13, 1998                  49,167 shares

         On or after the first day of                     The prior month's
           every month but on or before the               amount less
           last day of such month                         shares 833 shares



         For  purposes  of this  Agreement,  "Cause"  shall mean  misconduct  by
Purchaser,  including (i) conviction of any felony or any crime  involving moral
turpitude or  dishonesty;  (ii)  participation  in a fraud or act of  dishonesty
against the  Company;  (iii)  willful  breach of the  Company's  policies;  (iv)
intentional damage to the Company's property;  or (v) conduct by Purchaser which
in the good faith and reasonable  determination of the Board  demonstrates gross
unfitness to serve. Physical or mental disability shall not constitute "Cause. "
For purposes of this  Agreement,  any material  diminution in  responsibilities,
duties or  compensation  other than for Cause will be  treated,  upon  notice by
Purchaser to the Company, as a termination without Cause.


                                      61.
<PAGE>
                                    Exhibit C

                            JOINT ESCROW INSTRUCTIONS

Secretary
Lynx Therapeutics, Inc.
3832 Bay Center Place
Hayward, CA 94545

Dear Sir:

         As  Escrow  Agent  for  both  Lynx   Therapeutics,   Inc.,  a  Delaware
corporation  ("Company"),  and the undersigned purchaser of stock of the Company
("Purchaser"),  you are hereby  authorized  and  directed to hold the  documents
delivered to you pursuant to the terms of that certain Stock Purchase  Agreement
("Agreement"),  dated,  April 14,  1997,  to which a copy of these Joint  Escrow
Instructions  is  attached  as  Exhibit  C, in  accordance  with  the  following
instructions:

         1. In the event that the Company or an assignee shall elect to exercise
the Purchase Option set forth in the Agreement, the Company or its assignee will
give to Purchaser and you a written  notice  specifying  the number of shares of
stock to be purchased,  the purchase price, and the time for a closing hereunder
at the  principal  office  of the  Company.  Purchaser  and the  Company  hereby
irrevocably  authorize and direct you to close the  transaction  contemplated by
such notice in accordance with the terms of said notice.

         2. At the closing you are directed  to: (a) date any stock  assignments
necessary  for the transfer in question,  (b) fill in the number of shares being
transferred,  and (c) deliver same, together with the certificate evidencing the
shares of stock to be  transferred,  to the  Company  against  the  simultaneous
delivery to you of the purchase price (which may include suitable acknowledgment
of  cancellation  of  indebtedness)  of the  number  of  shares  of stock  being
purchased pursuant to the exercise of the Purchase Option.

         3. Purchaser irrevocably authorizes the Company to deposit with you any
certificates  evidencing  shares  of stock to be held by you  hereunder  and any
additions  and  substitutions  to said  shares as  specified  in the  Agreement.
Purchaser   does  hereby   irrevocably   constitute   and  appoint  you  as  his
attorney-in-fact  and agent for the term of this escrow to execute  with respect
to such  securities  and other  property  all  documents  of  assignment  and/or
transfer  and all  stock  certificates  necessary  or  appropriate  to make  all
securities negotiable and complete any transaction herein contemplated.

         4. This escrow shall  terminate upon  expiration or exercise in full of
the Purchase Option, whichever occurs first.

         5. If, at the time of  termination  of this escrow,  you should have in
your  possession  any  documents,  securities,  or other  property  belonging to
Purchaser, you shall deliver all of same to Purchaser and shall be discharged of
all further obligations  hereunder;  provided,  however,  that if at the time of
termination  of this  escrow you are advised by the  Company  that the  property
subject to this escrow is the subject of a pledge or other  security  agreement,
you  shall  deliver  all such  property  to the  pledgeholder  or  other  person
designated by the Company.

         6. Except as  otherwise  provided in these Joint  Escrow  Instructions,
your duties  hereunder  may be altered,  amended,  modified or revoked only by a
writing signed by all of the parties hereto.

         7. You shall be obligated  only for the  performance  of such duties as
are specifically set forth herein and may rely and shall be protected in relying
or refraining  from acting on any  instrument  reasonably  believed by you to be
genuine and to have been signed or  presented  by the proper party or parties or
their  assignees.  You shall not be personally  liable for any act you may do or
omit to do hereunder as Escrow Agent or as attorney-in-fact  for Purchaser while
acting in good faith,  and any act done or omitted by you pursuant to the advice
of your own attorneys shall be conclusive evidence of such good faith.

                                      62.
<PAGE>

         8.  You  are  hereby  expressly  authorized  to  disregard  any and all
warnings  given  by  any  of the  parties  hereto  or by  any  other  person  or
corporation,  excepting  only  orders or process  of courts of law,  and you are
hereby expressly authorized to comply with and obey orders, judgments or decrees
of any court. In case you obey or comply with any such order, judgment or decree
of any  court,  you shall not be liable to any of the  parties  hereto or to any
other person, firm or corporation by reason of such compliance,  notwithstanding
any such  order,  judgment  or decree  being  subsequently  reversed,  modified,
annulled, set aside, vacated or found to have been entered without jurisdiction.

         9. You shall not be liable in any  respect on account of the  identity,
authority or rights of the parties  executing or  delivering  or  purporting  to
execute or deliver the Agreement or any documents or papers  deposited or called
for hereunder.

         10. You shall not be liable for the  outlawing  of any rights under any
statute of limitations  with respect to these Joint Escrow  Instructions  or any
documents deposited with you.

         11.  You shall be  entitled  to employ  such legal  counsel  (including
without  limitation the firm of Cooley Godward LLP) and other experts as you may
deem  necessary  properly  to advise  you in  connection  with your  obligations
hereunder,  may rely upon the advice of such  counsel,  and may pay such counsel
reasonable compensation therefor.

         12. Your  responsibilities as Escrow Agent hereunder shall terminate if
you shall cease to be Secretary of the Company or if you shall resign by written
notice to each  party.  In the event of any such  termination,  the  Company may
appoint any officer or  assistant  officer of the  Company as  successor  Escrow
Agent and  Purchaser  hereby  confirms  the  appointment  of such  successor  or
successors  as his  attorney-in-fact  and  agent  to the  full  extent  of  your
appointment.

         13.  If  you  reasonably  require  other  or  further   instruments  in
connection  with these  Joint  Escrow  Instructions  or  obligations  in respect
hereto, the necessary parties hereto shall join in furnishing such instruments.

         14. It is  understood  and agreed that  should any  dispute  arise with
respect  to  the  delivery  and/or  ownership  or  right  of  possession  of the
securities, you may (but are not obligated to) retain in your possession without
liability to anyone all or any part of such securities  until such dispute shall
have been settled either by mutual written agreement of the parties concerned or
by a final order, decree or judgment of a court of competent  jurisdiction after
the time for appeal has expired and no appeal has been perfected,  but you shall
be under no duty whatsoever to institute or defend any such proceedings.

         15.  Any  notice  required  or  permitted  hereunder  shall be given in
writing and shall be deemed  effectively  given upon  personal  delivery or upon
deposit in any United  States Post Box, by  registered  or  certified  mail with
postage  and fees  prepaid,  addressed  to each of the  other  parties  hereunto
entitled at the following  addresses,  or at such other addresses as a party may
designate by ten (l0) days' written notice to each of the other parties hereto:

         COMPANY:             Lynx Therapeutics, Inc.
                              3832 Bay Center Place
                              Hayward, CA 94545
                              Attn:  Chief Executive Officer

         PURCHASER:           EDWARD C. ALBINI
                              79 QUAIL COURT
                              ATHERTON, CA  94027

         ESCROW AGENT:        Secretary
                              Lynx Therapeutics, Inc.
                              3832 Bay Center Place
                              Hayward, CA 94545

                                      63.
<PAGE>

         16. By  signing  these  Joint  Escrow  Instructions  you become a party
hereto only for the purpose of such Joint Escrow Instructions; you do not become
a party to the Agreement.

         17. This  instrument  shall be binding upon and inure to the benefit of
the parties hereto, and their respective successors and permitted assigns. It is
understood  and agreed that  references  to "you" or "your"  herein refer to the
original  Escrow  Agent  and to any  and  all  successor  Escrow  Agents.  It is
understood  and agreed that the Company and Lynx may at any time or from time to
time assign its rights under the Agreement  and these Joint Escrow  Instructions
in whole or in part.

                                            Very truly yours,

                                            LYNX THERAPEUTICS, INC.


                                            By: /s/ Sam Eletr
                                                -------------------------------

                                            Title:  Chief Executive Officer
                                                  -----------------------------


                                            PURCHASER:


                                                /s/ Edward C. Albini
                                            -----------------------------------
                                            Edward C. Albini

ESCROW AGENT:


/s/ James C. Kitch
---------------------------------
James C. Kitch, Secretary
Lynx Therapeutics, Inc.

                                      64.
<PAGE>

                                    EXHIBIT B

                      ASSIGNMENT SEPARATE FROM CERTIFICATE

FOR VALUE  RECEIVED  Edward C. Albini hereby sells,  assigns and transfers  unto
Lynx Therapeutics,  Inc., a Delaware Corporation  ("Company"),  pursuant to that
certain Stock Purchase  Agreement dated as of April 14, 1997 between the Company
and  the  undersigned  (the   "Agreement____________________  )  shares  of  the
Company's  Common Stock,  standing in its name on the books of said  corporation
represented by Certificate  ______________ herewith, and does hereby irrevocably
constitute and appoint the Company's  Attorney to transfer the said stock on the
books of the said  corporation  with full power of substitution in the premises.
This Assignment may be used only in accordance with and subject to the terms and
conditions  of the  Agreement,  in connection  with the  repurchase of shares of
Common Stock issued to the  undersigned  pursuant to the Agreement,  and only to
the extent that such shares  remain  subject to the  Company's  Purchase  Option
under the Agreement.


         Dated:________________


                                        Signature:  /s/ Edward C. Albini
                                                  -----------------------------

                                        Print Name:    Edward C. Albini
                                                   ----------------------------

                                      65.
<PAGE>

                                    Exhibit E

                                 PROMISSORY NOTE

$250,000                                                     Hayward, California
                                                                  April 14, 1997

     For Value Received, the undersigned hereby unconditionally  promises to pay
to the  order  of Lynx  Therapeutics,  Inc.,  a  Delaware  corporation  the (the
"Company"),  at 3832 Bay Center Place, Hayward, CA 94545, or at such other place
as the holder  hereof  may  designate  in writing in lawful  money of the United
States of America and  immediately  available  funds,  the  principal sum of two
hundred fifty  thousand  ($250,000.00)  together with interest  accrued from the
date  hereof on the  unpaid  principal  at the rate of 6.49% per  annum,  or the
maximum rate permissible by law (which under the laws of the State of California
shall be deemed to be the laws  relating  to  permissible  rates of  interest on
commercial loans), whichever is less, as follows:

           Principal Repayment. The outstanding principal amount hereunder shall
     be due and payable in full on April 13, 2002,  subject to earlier repayment
     as follows:  If the undersigned sells shares of stock subject to the Pledge
     Agreement of even date herewith  between the  undersigned  and the Company,
     then within  twenty (20) days of such sale,  the  undersigned  shall pay as
     principal  repayment,  $5.00  per  share  for each  share  sold  until  the
     undersigned  sells  fifty  thousand  (50,000)  shares  subject  the  Pledge
     Agreement; and

           Interest Payments.  Interest shall be payable upon the expiration or,
     termination  of this Note and shall be calculated on the basis of a 360-day
     year for the actual number of days elapsed;

provided,  however,  that in the event that the  undersigned's  employment by or
association  with the Company is  terminated  for any reason prior to payment in
full of this  Note,  this Note shall be  accelerated  and all  remaining  unpaid
principal and interest hereunder shall become due and payable  immediately after
such termination.

     If the  undersigned  fails to pay any of the principal  hereunder when due,
then the Company,  at its sole option,  shall have the right to accelerate  this
Note,  in which event the entire  principal  balance  and all  accrued  interest
hereunder immediately shall become due and payable, and immediately  collectible
by the Company pursuant to applicable law.

     This Note may be prepaid at any time without penalty. All money paid toward
the  satisfaction of this Note shall be applied first to the payment of interest
as required hereunder and then to the retirement of the principal.

     The full  amount  of this Note is  secured  by a pledge of shares of Common
Stock of the Company,  and is subject to all of the terms and  provisions of the
Stock Purchase  Agreement and the Pledge  Agreement,  each of even date herewith
between the undersigned and the Company.

     The  undersigned  hereby  represents  and agrees that the amounts due under
this Note are not consumer  debt,  and are not incurred  primarily for personal,
family or household purposes, but are for business and commercial purposes only.

     The undersigned hereby waives  presentment,  protest and notice of protest,
demand  for  payment,  notice of  dishonor  and all other  notices or demands in
connection with the delivery, acceptance, performance, default or endorsement of
this Note.

     The holder hereof shall be entitled to recover,  and the undersigned agrees
to pay when  incurred,  all costs  and  expenses  of  collection  of this  Note,
including without limitation, reasonable attorney's fees.

     This Note shall be governed by, and construed,  enforced and interpreted in
accordance  with the laws of the State of  California,  as applied to  contracts
made and performed entirely within the State by its residents.

                                         Signed  /s/ Edward C. Albini
                                                 -----------------------------
                                                 Edward C. Albini

                                      66.
<PAGE>

                                    Exhibit F

                                PLEDGE AGREEMENT


         1. As collateral  security for the payment of that certain  $250,000.00
promissory note issued this date to Lynx Therapeutics,  Inc.  ("Pledgee") by the
undersigned (hereinafter called "indebtedness"), the undersigned hereby assigns,
transfers  to and pledges with the Pledgee the  securities  listed on Schedule 1
hereto  which,  on the date hereof,  were  delivered  for deposit with  Pledgee,
together with any stock rights,  rights to subscribe,  dividends paid in cash or
other  property  in  connection  with the  complete  or partial  liquidation  of
Pledgee,  stock  dividends,  dividends  paid in stock,  new  securities or other
property  except cash dividends  other than  liquidating  dividends to which the
undersigned  is or may hereafter  become  entitled to receive on account of such
property,  and  in the  event  that  the  undersigned  receives  any  such,  the
undersigned  immediately  will  deliver  it to  Pledgee  to be held  by  Pledgee
hereunder in the same manner as the property  originally pledged hereunder.  All
property assigned,  transferred to and pledged with Pledgee under this paragraph
is hereinafter called "collateral."

         2. At any time,  without notice, and at the expense of the undersigned,
Pledgee in its name or in the name of its nominee or of the undersigned may, but
shall not be obligated  to: (a) collect by legal  proceedings  or otherwise  all
dividends  (except cash dividends other than liquidating  dividends),  interest,
principal payments and other sums now or hereafter payable upon or on account of
said collateral; (b) enter into any extension, reorganization,  deposit, merger,
or  consolidation  agreement,  or any  agreement  in  any  wise  relating  to or
affecting the collateral,  and in connection  therewith may deposit or surrender
control of such  collateral  thereunder,  accept other  property in exchange for
such  collateral  and do and perform such acts and things as it may deem proper,
and any money or  property  received in exchange  for such  collateral  shall be
applied to the  indebtedness or thereafter held by it pursuant to the provisions
hereof;  (c)  insure,  process  and  preserve  the  collateral;  (d)  cause  the
collateral  to be  transferred  to its name or to the name of its  nominee;  (e)
exercise as to such collateral all the rights, powers, and remedies of an owner,
except that so long as the indebtedness is not in default the undersigned  shall
retain all voting rights as to the collateral.

         3. The  undersigned  agrees  to pay  prior to  delinquency  all  taxes,
charges,  liens and assessments against the collateral,  and upon the failure of
the undersigned to do so, Pledgee at its option may pay any of them and shall be
the sole judge of the legality or validity  thereof and the amount  necessary to
discharge the same.

         4. All  advances,  charges,  costs and expenses,  including  reasonable
attorneys' fees,  incurred or paid by Pledgee in exercising any right,  power or
remedy conferred by this agreement,  or in the enforcement thereof, shall become
a part of the indebtedness secured hereunder and shall be paid to Pledgee by the
undersigned immediately and without demand.

         5. At the option of Pledgee and without  necessity of demand or notice,
all or any part of the indebtedness of the undersigned  immediately shall become
due and payable  irrespective of any agreed maturity,  upon the happening of any
of the  following  events:  (a)  failure to keep or perform  any of the terms or
provisions  of this  agreement;  (b)  default  in the  payment of  principal  or
interest  when due; (c) the levy of any  attachment,  execution or other process
against  the  collateral;  or  (d)  the  insolvency,  commission  of an  act  of
bankruptcy,  general  assignment  for the  benefit of  creditors,  filing of any
petition in  bankruptcy  or for relief under the  provisions  of Title 11 of the
United States Code of, by, or against the undersigned.

         6. In the event of the nonpayment of any indebtedness when due, whether
by  acceleration  or  otherwise,  or upon  the  happening  of any of the  events
specified in paragraph 5, Pledgee may then,  or at any time  thereafter,  at its
election,  apply,  set off,  collect or sell in one or more sales,  or take such
steps as may be  necessary  to  liquidate  and  reduce  to cash in the  hands of
Pledgee in whole or in part,  with or without any previous  demands or demand of
performance or notice or advertisement,  the whole or any part of the collateral
in such order as  Pledgee  may  elect,  and any such sale may be made  either at
public or private sale at its place of business or elsewhere, or at any broker's
board or  securities  exchange,  either  for cash or upon  credit or for  future
delivery;  provided,  however, that if such disposition is at private sale, then
the purchase price of the  collateral  shall be equal to the public market price

                                      67.
<PAGE>

then in effect,  or, if at the time of sale no public market for the  collateral
exists,  then, in recognition of the fact that the sale of the collateral  would
have to be registered under the Securities Act of 1933, as amended, and that the
expenses of such  registration  are  commercially  unreasonable for the type and
amount of collateral pledged hereunder, Pledgee and the undersigned hereby agree
that such  private  sale  shall be at a  purchase  price  mutually  agreed to by
Pledgee  and the  undersigned  or, if the parties  cannot  agree upon a purchase
price,  then at a purchase price  established by a majority of three independent
appraisers  knowledgeable  of the  value of such  collateral,  one  named by the
undersigned  within 10 days after  written  request by the Pledgee to do so, one
named by  Pledgee  within  such 10 day  period,  and the third  named by the two
appraisers so selected, with the appraisal to be rendered by such body within 30
days of the  appointment  of the third  appraiser.  The cost of such  appraisal,
including all appraiser's fees, shall be charged against the proceeds of sale as
an expense of such sale.  Pledgee may be the purchaser of any or all  collateral
so sold and hold the same thereafter in its own right free from any claim of the
undersigned or right of  redemption.  Demands of  performance,  notices of sale,
advertisements  and presence of property at sale are hereby waived,  and Pledgee
is hereby  authorized to sell  hereunder any evidence of debt pledged to it. Any
sale hereunder may be conducted by any officer or agent of Pledgee.

         7.  The  proceeds  of the  sale of any of the  collateral  and all sums
received or collected by Pledgee from or on account of such collateral  shall be
applied by Pledgee to the  payment of  expenses  incurred  or paid by Pledgee in
connection with any sale, transfer or delivery of the collateral, to the payment
of any other costs,  charges,  attorneys' fees or expenses mentioned herein, and
to the payment of the  indebtedness  or any part  hereof,  all in such order and
manner as Pledgee in its discretion may determine. Pledgee shall pay any balance
to the undersigned.

         8. Pledgee shall be under no duty or  obligation  whatsoever to make or
give any  presentments,  demands for  performance,  notices of  non-performance,
protests,  notices of protest or notices  of  dishonor  in  connection  with any
obligations or evidences of  indebtedness  held by Pledgee as collateral,  or in
connection with any obligations or evidences of indebtedness which constitute in
whole or in part the indebtedness secured hereunder.

         9. Pledgee at any time may deliver the  collateral  or any part thereof
to the undersigned  and the receipt of the  undersigned  shall be a complete and
full  acquittance for the collateral so delivered,  and Pledgee shall thereafter
be discharged from any liability or responsibility therefor.

         10. Upon the transfer of all or any part of the  indebtedness,  Pledgee
may transfer  all or any part of the  collateral  and shall be fully  discharged
thereafter from all liability and responsibility with respect to such collateral
so  transferred,  and the  transferee  shall be vested  with all the  rights and
powers of Pledgee hereunder with respect to such collateral so transferred;  but
with  respect to any  collateral  not so  transferred  Pledgee  shall retain all
rights and powers hereby given.

         11. Until all  indebtedness  shall have been paid in full, the power of
sale and all other  rights,  powers and  remedies  granted to Pledgee  hereunder
shall  continue  to exist and may be  exercised  by Pledgee at any time and from
time to time  irrespective of the fact that the indebtedness or any part thereof
may have  become  barred by any  statute of  limitations,  or that the  personal
liability of the undersigned may have ceased.

         12. Pledgee agrees that so long as the  indebtedness is not in default,
shares  of  common  stock  of  Pledgee  held  hereunder  as  collateral  for the
indebtedness  shall be released from pledge as the  indebtedness is paid, at the
rate of one share for Five Dollars  ($5.00) of principal  amount of indebtedness
paid for the first Two Hundred Fifty  Thousand  Dollars  ($250,000) of principal
amount of indebtedness paid. Release from pledge,  however,  shall not result in
release from the provisions of those certain Joint Escrow  Instructions  of even
date  herewith  among the parties to this Pledge  Agreement and the Escrow Agent
named  therein,  from the  Purchase  Option of  Pledgee,  set forth in the Stock
Purchase  Agreement  of even date  herewith  between  the parties to this Pledge
Agreement.

         13. The rights,  powers and remedies given to Pledgee by this Agreement
shall be in  addition  to all rights,  powers and  remedies  given to Pledgee by
virtue of any statute or rule of law. Pledgee may exercise its Pledgee's lien or
right of setoff with  respect to the  indebtedness  in the same manner as if the
indebtedness  were unsecured.  Any forbearance or failure or delay by Pledgee in
exercising  any  right,  power or remedy  hereunder  shall not be deemed to be a
waiver of such right, power or remedy, and any single or partial exercise of any
right,  power or

                                      68.
<PAGE>

remedy  hereunder  shall not preclude the further  exercise  thereof;  and every
right, power and remedy of Pledgee shall continue in full force and effect until
such right,  power or remedy is specifically  waived by an instrument in writing
executed by Pledgee.

Dated:  April 14, 1997




                                                 /s/ Edward C. Albini
                                                 -----------------------------
                                                 Edward C. Albini


ATTACHMENT:

Schedule 1


                                      69.