Document:

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                                                                   Exhibit 10.10

                            LOAN AND PLEDGE AGREEMENT

      THIS LOAN AND PLEDGE AGREEMENT (this "Agreement") dated as of October 30,
1998 is made by Henry E. Blair (the "Borrower"), residing at 275 Mill Way,
Barnstable, Massachusetts 02630, in favor of Dyax Corp. ("Dyax"), a Delaware
corporation with its principal place of business at One Kendall Square, Building
600, Cambridge, Massachusetts 02139.

                                    RECITALS

      A. The Borrower desires to borrow $1,300,000 from Dyax in order to finance
the purchase of (i) shares of stock in the cooperative corporation which owns
the building located at 68 Beacon Street, Boston, Massachusetts, which shares
will entitle the Borrower to occupy an apartment in such building ( the
"Apartment") and (ii) Unit 228 at the Brimmer Street Garage Condominium (the
"Brimmer Street Unit", and together with the Apartment, the "Real Estate").

      B. Dyax is willing to make the Loan (as defined below) upon the condition,
among others, that the Borrower enter into this Agreement and grant the security
interest and pledge hereinafter described to secure the Liabilities (as defined
in Section 16 hereof).

      NOW, THEREFORE, for and in consideration of the premises and the Loan made
by Dyax and other good and valuable consideration, the receipt of which is
hereby acknowledged, and intending to be legally bound hereby, the parties
hereby agree as follows:

      1. Loan. Subject to the terms hereof, Dyax will make, on or after the date
hereof, two loans (severally and collectively referred to herein as the "Loan")
to the Borrower in the aggregate principal amounts of $600,000 and $700,000,
respectively. The Loan shall be payable in full on the fifth anniversary of the
date hereof (the "Maturity Date").

      2. Notes. The Loan shall be evidenced by promissory notes of the Borrower
in the original principal amounts of $600,000 and $700,000, respectively
(severally and collectively referred to herein as the "Notes"), payable to Dyax
with a final maturity date of the Maturity Date, such Notes to be substantially
in the form of Exhibit A and Exhibit B attached hereto. The Notes shall be dated
the date of the Loan and shall have the blanks therein appropriately completed.

      3. Interest Rate. The Loan shall bear interest on the outstanding
principal amount thereof at a percentage rate per annum equal to the Base Rate
of BankBoston, N.A. less one and one half percent (1.5%), but in any event not
less than the applicable federal rate necessary to avoid imputation of interest
under sections 1274 or 7872 of the Internal Revenue Code of 1986 (or
corresponding provisions of subsequent laws), as amended.
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      4. Payments and Prepayments of the Loan. Two monthly payments of Three
Thousand Seven Hundred Ninety Three and 76/100 Dollars ($3,793.76) and Four
Thousand Four Hundred Twenty Six and 05/100 Dollars ($4,426.05), respectively,
shall be due and payable on the first day of each month beginning on December 1,
1998, and such monthly payments shall be applied first to the payment of
interest and any remainder shall be applied to reduce the outstanding principal
amount of the Loan. The balance of any unpaid principal and all accrued and
unpaid interest thereon shall be due and payable on the Maturity Date. The
Borrower may prepay the Loan and the Notes in whole or in part at any time
without premium or penalty, together with all unpaid interest thereon and all
other amounts due hereunder.

      5. Conditions Precedent to Loan. The obligation of Dyax to make the Loan
is subject to the condition precedent that Dyax shall have received, in form and
substance satisfactory to Dyax and its counsel, the following:

      (a) this Agreement and the Notes, duly executed by the Borrower;

      (b) the Pledged Collateral with stock powers for the Pledged Collateral
duly executed by the Borrower;

      (c) a certain Cooperative Pledge Agreement, dated as of the date hereof,
granted by the Borrower in favor of Dyax, which Cooperative Pledge Agreement
grants a security interest in the shares of stock of the cooperative corporation
owning the Apartment, duly executed by the Borrower and the collateral pledged
thereunder with stock powers for such pledged collateral duly executed by the
Borrower;

      (d) a certain Mortgage, dated as of the date hereof, from the Borrower to
Dyax, which Mortgage grants a lien on the Brimmer Street Unit, duly executed by
the Borrower; and

      (e) such other documents, and completion of such other matters, as Dyax
may deem necessary or appropriate.

      6. Security Interest and Pledge. To secure the prompt, punctual, and
faithful performance of all and each of the present and future Liabilities of
the Borrower to Dyax, the Borrower hereby grants to Dyax, a security interest in
and to, and assigns, pledges, and delivers to Dyax certificates representing all
shares of the Class A Preferred Stock of Dyax issued to the Borrower as of the
date hereof or issuable to the Borrower hereafter ("Pledged Securities"),
together with appropriate undated stock powers duly executed in blank, and all
products, proceeds, substitutions, additions, interest, dividends, and other
distributions in respect thereto, as described in Section 7 below (all of which
are referred to hereinafter as the "Collateral").

      7. Stock Dividends, Distributions, Etc. If, while this Agreement is in
effect, the Borrower shall become entitled to receive or shall receive any stock
certificate (including, without limitation, any certificate representing a stock
dividend or a distribution in connection with any reclassification, increase or
reduction of capital, or issued in connection with any reorganization), whether
as an addition to, in substitution of or in exchange for any shares of any
Pledged Securities, or otherwise, the Borrower agrees to accept the same as
agent for Dyax and

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to hold the same in trust on behalf of and for the benefit of Dyax and to
deliver the same forthwith to Dyax in the exact form received, with the
indorsement of the Borrower when necessary and/or with appropriate undated stock
powers duly executed in blank, to be held by Dyax as part of the Collateral. In
case any distribution of capital shall be made on or in respect of the Pledged
Securities or any property shall be distributed upon or with respect to the
Pledged Securities pursuant to the recapitalization or reclassification of the
capital of Dyax or pursuant to the reorganization thereof, the property so
distributed shall be delivered to Dyax as Collateral. All sums of money and
property so paid or distributed in respect of the Pledged Securities which are
received by the Borrower shall, until paid or delivered to Dyax, be held by the
Borrower in trust as Collateral.

      8. Cash Dividends; Voting Rights. Unless a Default (as defined in Section
11) has occurred and is continuing, the Borrower shall be entitled to receive
all cash dividends paid in respect of the Pledged Securities, to vote the
Pledged Securities and to give consents, waivers and ratifications, and to take
other action in respect of the Pledged Securities. After the occurrence and
during the continuance of any Default, Dyax shall have the right, upon notice to
the Borrower, to receive all cash dividends paid in respect of the Pledged
Securities and to exercise voting rights as specified in Section 12 below.

      9. Borrower's Representations. The Borrower hereby represents, warrants
and covenants as follows:

            (a) The Borrower has the full power, authority and legal right to
enter into this Agreement to be bound hereby and to perform and observe the
terms and conditions hereof, and is in compliance with all applicable material
laws, rules and regulations.

            (b) This Agreement has been duly executed and delivered by the
Borrower and constitutes the legal, valid and binding obligation of the Borrower
enforceable against him in accordance with its terms, subject, as to the
enforcement of remedies, to applicable bankruptcy, reorganization, insolvency
and similar laws affecting creditors' rights generally and to moratorium laws
from time to time in effect and to general principles of equity.

            (c) The execution, delivery and performance by the Borrower of this
Agreement does not and will not (i) violate or constitute a default under any
provision of any agreement, note or instrument which is binding upon the
Borrower or by which his properties are bound or materially affected, or any
law, rule or regulation, order writ, injunction or decree of any court or
governmental instrumentality or any contractual restriction binding on the
Borrower, or (ii) require any filing with or consent or other act by or in
respect of any governmental authority or other person or entity (other than the
filing of the appropriate number of UCC-1 financing statements covering the
Pledged Securities, if necessary, and any consent obtained by the Borrower prior
to the date hereof) or (iii) constitute a default thereunder or result in the
imposition or require the creation of any lien or charge (other than those
created, continued or otherwise contemplated hereby) upon the assets of the
Borrower.

            (d) The Pledged Securities consist of not fewer than 431,056 shares
of Class A Series 1 Preferred Stock, 246,040 shares of Class A Series 3
Preferred Stock, 129,713 shares of Class A Series 4 Preferred Stock and 18,350
shares of Class A Series 5 Preferred Stock, of

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Dyax and are held and owned by the Borrower free and clear of all liens,
encumbrances, attachments, security interests, pledges and charges, other than
those in favor of Dyax.

            (e) The Borrower as of the date hereof has a net worth, defined as
the fair market value of total assets, exclusive of assets subject to contingent
liabilities, less total liabilities, of at least $10,000,000.

      10. Borrower's Covenants. The Borrower shall

            (a) if the Collateral is in the form of a certificated security,
within the meaning of the Uniform Commercial Code, as adopted in the
Commonwealth of Massachusetts (the "Code"), surrender possession of the
Collateral to Dyax;

            (b) if the Collateral is in the form of an uncertificated security,
within the meaning of the Code, cause Dyax to record this pledge in the records
of Dyax relating to the Pledged Securities;

            (c) execute all such instruments, documents, and papers, and will do
all such acts as Dyax may reasonably request now and from time to time hereafter
with respect to the perfection of the security interest granted herein and the
assignment effected hereby, including without limitation making payments of the
proceeds of the Loan and such additional amounts as are necessary to cause the
current pledgee of the certificates for the Pledged Securities to deliver such
certificates to Dyax;

            (d) keep the Collateral free and clear of all liens, encumbrances,
attachments, security interests, pledges, and charges, except in favor of Dyax
or created by Dyax;

            (e) deliver to Dyax, if and when received by the Borrower, any item
representing or constituting any of the Collateral or, except as otherwise
provided herein, proceeds of Collateral;

            (f) not cause or permit any of the Collateral presently evidenced by
a written certificate to be converted to uncertificated securities, except on
request of Dyax;

            (g) not exercise any right with respect to the Collateral which
would dilute or otherwise adversely affect Dyax's rights to the Collateral;

            (h) make a payment on the Loan or grant to Dyax a security interest
in and to, and assign, pledge and deliver to Dyax certificates representing
additional marketable securities issued to the Borrower, if necessary, in order
to ensure that at all times the value of the Collateral is not less than 150% of
the outstanding principal balance of the Loan; and

            (i) deliver to Dyax annually on September 30 a certificate stating
that (i) the Borrower as of the date thereof has a net worth, defined as the
fair market value of total assets, exclusive of assets subject to contingent
liabilities, less total liabilities, of at least $10,000,000 and (ii) the value
of the Collateral as of the date thereof is not less than 150% of the
outstanding principal balance of the Loan.

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      11. Default. Upon the occurrence of a Default, any and all Liabilities of
the Borrower to Dyax shall become immediately due and payable at the option of
Dyax and without further notice or demand, in addition to which Dyax may
exercise Dyax's rights and remedies upon Default, as set forth hereinafter. For
purposes of this Agreement, a "Default" under this Agreement shall mean any of
the following events: (i) an Event of Default under any Note, (ii) any
representation or warranty made by the Borrower in this Agreement being untrue
in any material respect when made, or (iii) failure of the Borrower to observe
or perform any other covenant, agreement or other term of this Agreement and the
continuation of such failure without it having been duly cured for a period of
thirty (30) days after written notice thereof given by Dyax to the Borrower.

      12. Effect of Default. Upon the occurrence of any Default, and at any time
thereafter, unless and until the Default may be cured, Dyax shall have the right
to apply the Collateral toward the satisfaction of the Liabilities, to sell or
otherwise dispose of the Collateral and/or enforce and collect the Collateral
for application towards (but not necessarily in complete satisfaction) of the
Liabilities, in addition to all of the rights and remedies of a secured party
upon default under the Code. The Borrower shall remain liable to Dyax for any
deficiency remaining following such application to any Liabilities. Any and all
shares of the Pledged Securities may be registered in the name of Dyax or its
nominee, and Dyax or its nominee may thereafter without further notice exercise
all voting and corporate rights at any meeting of any issuer and exercise any
and all rights of conversion, exchange, subscription or any other rights,
privileges or options pertaining to any shares of the Pledged Securities as if
it were the absolute owner thereof, including without limitation, the right to
exchange at its discretion any and all of the Pledged Securities upon the
merger, consolidation, reorganization, recapitalization or other readjustment of
any issuer or upon the exercise by any issuer or Dyax or such nominee of any
right, privilege or option pertaining to any shares of the Pledged Securities,
and, in connection therewith, to deposit and deliver any and all of the Pledged
Securities with any committee, depositary, transfer agent, registrar or other
designated agency upon such terms and conditions as it may determine, all
without liability except to account for property actually received by it, but
Dyax shall have no duty to exercise any of the aforesaid rights, privileges or
options and shall not be responsible for any failure to do so or delay in so
doing so long as it acts in good faith. The Borrower acknowledges that any
exercise by Dyax of Dyax's rights upon default may be subject to compliance by
Dyax with state and/or federal law governing the sale of securities. Except as
otherwise provided herein, the net proceeds which Dyax shall receive from the
sale of the Collateral, in accordance with the provisions hereof, shall be
applied in the following manner: First, to the payment of all costs and expenses
incurred by Dyax in connection with the administration and enforcement of, or
the preservation of any rights under, or otherwise in connection with this
Agreement (including, without limitation, the costs and expenses of retaking,
holding, preparing for sale or selling of any Collateral and the reasonable fees
and disbursements of its counsel and agents); Second, to the payment of all
other Liabilities in such order of priority as Dyax may determine in its sole
discretion; and Third, as otherwise provided by applicable law.

      13. Private Placements.

      (a) The Borrower recognizes that Dyax may be unable to effect a public
sale of any or all of the Pledged Securities by reason of certain prohibitions
contained in the federal

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securities laws and applicable state or foreign securities law, but may resort
to one or more private sales thereof to a restricted group of purchasers who
will be obliged to agree, among other things, to acquire such securities for
their own account for investment and not with a view to the distribution or
resale thereof. The Borrower acknowledges and agrees that any such private sale
may result in prices and other terms less favorable to the seller than if such
sale were a public sale and, notwithstanding such circumstances, agrees that any
such private sale shall be deemed to have been made in a commercially reasonable
manner. Dyax shall be under no obligation to delay a sale of any of the Pledged
Securities for the period of time necessary to permit the issuer of such
securities to register such securities for public sale under the federal
securities law, or under applicable state securities law, even if the issuer
would agree to do so.

      (b) The Borrower further agrees to use commercially reasonable efforts to
do or cause to be done all such other acts and things (other than effect the
registration of the Pledged Securities under applicable federal, state or
foreign laws) as may be necessary to make such sale or sales of any portion or
all of the Pledged Securities valid and binding and in compliance with any and
all applicable laws, regulations, orders, writs, injunctions, decrees or awards
of any and all courts, arbitrators or governmental instrumentalities, domestic
or foreign, having jurisdiction over any such sale or sales, all at the
Borrower's expense. The Borrower further agrees that a breach of any of the
covenants contained in this Section 13 will cause irreparable injury to Dyax,
and that Dyax will have no adequate remedy at law in respect of such breach and,
as a consequence, agrees that each and every covenant contained in this Section
13 shall be specifically enforceable against the Borrower.

      14. Appointment of Dyax as Attorney-in-Fact. In furtherance of the
remedies provided in Sections 12 and 13, the Borrower hereby designates Dyax as
and for the attorney-in-fact of the Borrower after the occurrence and during the
continuance of a Default to endorse in favor of Dyax any of the Collateral, to
cause the transfer of any of the Collateral in such name as Dyax may from time
to time determine, to cause the issuance of certificates for book entry and/or
uncertificated securities, and to make demand and to initiate actions to
accomplish the purposes of this Agreement. In connection with any action to
enforce any of the Collateral, Dyax may make such compromise or settlement with
respect to the Collateral as Dyax determines to be appropriate. After and during
the continuance of a Default, and in furtherance of the remedies provided in
Sections 12 and 13, Dyax shall also have and may exercise at any time all
rights, remedies, powers, and discretions of the Borrower with respect to and
under the Collateral. The within designation, being coupled with an interest, is
irrevocable until the within instrument is terminated by a written instrument
executed by a duly authorized officer of Dyax. Dyax shall not be liable for any
act or omission to act pursuant to this Paragraph except for any act or omission
to act which is in actual bad faith or which is grossly negligent.

      15. Cumulative Remedies. The rights, remedies, powers, privileges, and
discretions of Dyax hereunder (hereinafter, "Dyax's Rights and Remedies") shall
be cumulative and not exclusive of any rights or remedies which it otherwise may
have. No delay or omission by Dyax in exercising or enforcing any of Dyax's
Rights and Remedies shall operate as, or constitute, a waiver thereof. No waiver
by Dyax of any Default or of any default under any other agreement shall operate
as a waiver of any other default hereunder or under any other agreement. No
exercise of any of Dyax's Rights and Remedies and no other agreement or
transaction of

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whatever nature entered into between Dyax and the Borrower at any time shall
preclude any other exercise of Dyax's Rights and Remedies. No waiver by Dyax of
any of Dyax's Rights and Remedies on any one occasion shall be deemed a waiver
on any subsequent occasion, nor shall it be deemed a continuing waiver. All of
Dyax's Rights and Remedies and all of Dyax's rights, remedies, powers,
privileges, and discretions under any other agreement or transaction are
cumulative and not alternative or exclusive and may be exercised by Dyax at such
time or times and in such order of preference as Dyax in its sole discretion may
determine.

      16. Definition of Liabilities. "Liabilities" shall mean (i) all
indebtedness, obligations and liabilities of the Borrower, whether of principal,
interest, fees, expenses or otherwise, now existing or hereafter contracted or
incurred under or in connection with the Loan and any and all extensions,
renewals, refinancings and refunding of any such indebtedness in whole or in
part, (ii) all costs and expenses incurred by Dyax in the collection of any of
such Borrower indebtedness, including without limitation reasonable attorneys'
fees and legal expenses, and (iii) all future advances made by Dyax for the
protection or preservation of the Collateral or any portion thereof.

      17. Waivers by Borrower. The Borrower

            (a) waives presentment, demand, notice, and protest with respect to
the Liabilities and the Collateral; and

            (b) waives any delay on the part of Dyax; and

            (c) assents to any indulgence or waiver which Dyax may grant or give
to the Borrower or any other person liable or obliged to Dyax for or on the
Liabilities; and

            (d) agrees that no release of any property securing the Liabilities
shall affect the rights of Dyax with respect to the Collateral hereunder; and

            (e) if entitled thereto, waives the right to notice and/or hearing
prior to Dyax's exercising of Dyax's rights and remedies hereunder upon default.

      18. Partial Release Upon Pay-Down of the Notes. Upon written notice from
the Borrower that he wishes to sell some or all of the Pledged Securities and
apply the proceeds of such sale to amounts due under the Notes, Dyax agrees to
deliver promptly to a broker designated by the Borrower and reasonably
satisfactory to Dyax certificates representing such Pledged Securities, provided
that such instructions include or are accompanied by irrevocable instruction
from the Borrower (with signature guarantee) to the broker requiring that the
net proceeds from the sale of such Pledged Securities be delivered by check
payable to Dyax and that a certificate for any shares of the Pledged Securities
remaining unsold be returned to Dyax.

      19. Duties of Dyax. Dyax shall have no duty as to the collection or
protection of the Collateral or any income or distribution thereon, beyond the
safe custody of such of the Collateral as may come into the possession of Dyax
and shall have no duty as to the preservation of rights against prior parties or
any other rights pertaining thereto. Dyax's Rights and Remedies may be exercised
without resort or regard to any other source of satisfaction of the Liabilities.

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      20. Binding Agreement. This Agreement shall be binding upon the Borrower
and upon the Borrower's representatives, successors, and assigns, and shall
enure to the benefit of Dyax and its successors and assigns.

      21. Complete Agreement. This Agreement and all other instruments executed
in connection herewith incorporate all discussions and negotiations among Dyax
and the Borrower concerning the matters included herein and in such other
instruments. No such discussions or negotiations shall limit, modify, or
otherwise affect the provisions hereof. No modification, amendment, or waiver of
any provision of this Agreement shall be effective unless executed in writing by
the party to be charged with such modification, amendment and waiver, and if
such party be Dyax, then by a duly authorized officer thereof other than the
Borrower.

      22. Use of Originals. This Agreement and all other documents in Dyax's
possession which relate to the Liabilities may be reproduced by Dyax by any
photographic, photostatic, microfilm, micro-card, miniature photographic,
xerographic, or similar process, and, with the exception of instruments
constituting the Collateral, Dyax may destroy the original from which any
document was so reproduced. Any such reproduction shall be admissible in
evidence as the original itself in any judicial or administrative proceeding
(whether or not the original is an existence and whether or not such
reproduction was made in the regular course of business) and any enlargement,
facsimile, or further reproduction shall likewise be admissible in evidence.

      23. Notices. All notices, requests, demands and other communications to be
given pursuant to this Agreement shall be in writing and shall be deemed to have
been duly given if delivered by hand or overnight courier or mailed by
registered or certified mail, return receipt requested, postage prepaid,
addressed to the party to receive notice at its or his respective address set
forth in the first paragraph of this Agreement or such other address as such
party shall have designated by notice in writing to the other party in
accordance with this section.

      24. Governing Law. This Agreement, and all rights and obligations
hereunder, including matters of construction, validity, and performance, shall
be governed by the laws of the Commonwealth of Massachusetts. The Borrower
submits to the jurisdiction of the courts of said Commonwealth for all purposes
with respect to this Agreement and the Borrower's relationships with Dyax.

      25. Sealed Instrument. It is intended that this Agreement take effect as a
sealed instrument.

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      IN WITNESS WHEREOF, the undersigned has executed the foregoing Loan and
Pledge Agreement as of the date first above written.

                          /s/ Henry E. Blair
                          ------------------------------
                          Henry E. Blair, individually

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                                                                     Exhibit A

                                 PROMISSORY NOTE

$600,000.00                                            Cambridge, Massachusetts
                                                               October 30, 1998

         For value received, the undersigned Henry E. Blair of Barnstable,
Massachusetts 02630 (the "Borrower"), promises to pay to Dyax Corp. ("Dyax"),
the principal sum of Six Hundred Thousand Dollars ($600,000.00), with interest
on the unpaid principal balance at a rate calculated as follows: the Base Rate
of BankBoston, N.A. less one and one half percent (1.5%) per annum, but in any
event not less than the applicable federal rate necessary to avoid imputation of
interest under sections 1274 or 7872 of the Internal Revenue Code of 1986 (or
corresponding provisions of subsequent laws), as amended. Interest shall accrue
from the date hereof on the unpaid principal balance. A monthly payment of Three
Thousand Seven Hundred Ninety Three and 76/100 Dollars ($3,793.76) shall be due
and payable on the first day of each month beginning on December 1, 1998, and
such monthly payments shall be applied first to the payment of interest and any
remainder shall be applied to reduce the principal balance hereof. The balance
of any unpaid principal and all accrued and unpaid interest thereon shall be due
and payable on October 30, 2003. Except as otherwise agreed to by the Borrower
and the holder, payments of principal and interest shall be made in lawful money
of the United States of America at the principal office of Dyax in
Massachusetts, or by check mailed to such other place as the holder hereof shall
designate.

         This note shall immediately become due and payable upon notice to the
Borrower after a vote taken at any time by the directors of Dyax who are not
Dyax employees, or a vote of the Compensation Committee of Dyax, to accelerate
payment of this note upon a determination, in the sole discretion of such
directors or such committee, that acceleration is in the best interest of Dyax,
including without limitation under the following circumstances: (i) termination
of the Borrower's service as Chairman and Chief Executive Officer of Dyax for
any reason; provided, however, that in the case of death or disability payment
shall not be due for at least twelve (12) months after termination; (ii) at any
time that Dyax's cash and marketable investments total less than $10,000,000;
and (iii) at any time that Dyax anticipates filing a registration statement for
an initial public offering of its Common Stock.

         If there occurs a default in the performance of any of the terms,
agreements, covenants or conditions contained in this note or the Mortgages (as
hereinafter defined) or the Cooperative Pledge Agreement (as hereinafter
defined) or the Loan and Pledge Agreement (as hereinafter defined) or any other
documents now or hereafter executed as security for this note or in furtherance
of Dyax's protections under the Mortgages (collectively, the "Loan Documents")
continuing beyond, in each case, any applicable grace period as may be provided
therein for the payment of such amount or the performance of such term,
agreement, covenant or condition, then at the option of the holder of this note
the entire indebtedness evidenced hereby, with interest

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accrued  thereon,  if any, shall become due and payable,  and no omission on the
part of the holder  hereof to exercise  such option when entitled to do so shall
be  construed  as a waiver of such right so long as such  default  shall  remain
uncured.

         The unpaid balance hereof may be paid in part or in full at any time
without penalty. All prepayments shall be applied first to the payment of
interest.

         This note is secured by (i) a certain leasehold mortgage (the
"Leasehold Mortgage") of even date herewith from the Borrower to Dyax , which
Leasehold Mortgage grants a lien on the interest of the Borrower in apartment
#7E in the building located at 68 Beacon Street, Boston, Massachusetts (the
"Apartment"), all as more particularly described in such Leasehold Mortgage;
(ii) a certain mortgage (together with the Leasehold Mortgage, the "Mortgages")
of even date herewith from the Borrower to Dyax, which mortgage grants a lien on
Unit 228 at the Brimmer Street Garage Condominium, Boston, Massachusetts
(together with the Apartment, the "Real Estate"), all as more particularly
described in such mortgage; (iii) a certain pledge agreement (the "Cooperative
Pledge Agreement") of even date herewith granted by the Borrower in favor of
Dyax; and (iv) a certain loan and pledge agreement (the "Loan and Pledge
Agreement") of even date herewith granted by the Borrower in favor of Dyax. Dyax
by its acceptance hereof, shall be entitled to the benefits, and subject to the
terms, of the Mortgages, the Cooperative Pledge Agreement and the Loan and
Pledge Agreement.

         If the Borrower conveys, transfers, assigns, encumbers, pledges or
otherwise disposes of any legal or beneficial interest in the Real Estate or in
the equity of redemption in the Real Estate or any part thereof without Dyax's
prior written consent, Dyax may, at its option, require immediate payment of the
entire indebtedness evidenced hereby, with accrued interest thereon, if any, as
provided herein.

         The undersigned agrees to pay, upon maturity (by acceleration or
otherwise), costs of collection, including reasonable attorneys' fees.

         No delay or omission on the part of the holder in exercising any right
hereunder shall operate as a waiver of such right or of any other right of such
holder; nor shall any delay, omission or waiver on any occasion be deemed a bar
to or waiver of the same or any other right on any future occasion. The
undersigned and every indorser or guarantor of this note regardless of the time,
order or place of signing waives presentment, demand, protest and notices of
every kind and assents to any one or more extensions or postponements of the
time of payment or any other indulgences, to any substitutions, exchanges or
releases of collateral if at any time there be available to the holder
collateral for this note, and to the additions or releases of any other parties
or persons primarily or secondarily liable.

         All rights and obligations hereunder shall be governed by and construed
in accordance with the law of the Commonwealth of Massachusetts and this note
shall be deemed to be under seal.

                                                 ------------------------------
                                                 Henry E. Blair, individually

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                                                                      Exhibit B

                                 PROMISSORY NOTE

$700,000.00                                            Cambridge, Massachusetts
                                                               October 30, 1998

         For value received, the undersigned Henry E. Blair of Barnstable,
Massachusetts 02630 (the "Borrower"), promises to pay to Dyax Corp. ("Dyax"),
the principal sum of Seven Hundred Thousand Dollars ($700,000.00), with interest
on the unpaid principal balance at a rate calculated as follows: the Base Rate
of BankBoston, N.A. less one and one half percent (1.5%) per annum, but in any
event not less than the applicable federal rate necessary to avoid imputation of
interest under sections 1274 or 7872 of the Internal Revenue Code of 1986 (or
corresponding provisions of subsequent laws), as amended. Interest shall accrue
from the date hereof on the unpaid principal balance. A monthly payment of Four
Thousand Four Hundred Twenty Six and 05/100 Dollars ($4,426.05) shall be due and
payable on the first day of each month beginning on December 1, 1998, and such
monthly payments shall be applied first to the payment of interest and any
remainder shall be applied to reduce the principal balance hereof. The balance
of any unpaid principal and all accrued and unpaid interest thereon shall be due
and payable on October 30, 2003. Except as otherwise agreed to by the Borrower
and the holder, payments of principal and interest shall be made in lawful money
of the United States of America at the principal office of Dyax in
Massachusetts, or by check mailed to such other place as the holder hereof shall
designate.

         This note shall immediately become due and payable upon notice to the
Borrower after a vote taken at any time by the directors of Dyax who are not
Dyax employees, or a vote of the Compensation Committee of Dyax, to accelerate
payment of this note upon a determination, in the sole discretion of such
directors or such committee, that acceleration is in the best interest of Dyax,
including without limitation under the following circumstances: (i) termination
of the Borrower's service as Chairman and Chief Executive Officer of Dyax for
any reason; provided, however, that in the case of death or disability payment
shall not be due for at least twelve (12) months after termination; (ii) at any
time that Dyax's cash and marketable investments total less than $10,000,000;
and (iii) at any time that Dyax anticipates filing a registration statement for
an initial public offering of its Common Stock.

         If there occurs a default in the performance of any of the terms,
agreements, covenants or conditions contained in this note or the Mortgage (as
hereinafter defined) or the Loan and Pledge Agreement (as hereinafter defined)
or any other documents now or hereafter executed as security for this note or in
furtherance of Dyax's protections under the Mortgage (collectively, the "Loan
Documents") continuing beyond, in each case, any applicable grace period as may
be provided therein for the payment of such amount or the performance of such
term, agreement, covenant or condition, then at the option of the holder of this
note the entire indebtedness evidenced hereby, with interest accrued thereon, if
any, shall become due and payable, and no omission on the part

                                         12

<PAGE>

of the holder  hereof to exercise  such  option when  entitled to do so shall be
construed  as a  waiver  of such  right  so long as such  default  shall  remain
uncured.

         The unpaid balance hereof may be paid in part or in full at any time
without penalty. All prepayments shall be applied first to the payment of
interest.

         This note is secured by (i) a certain mortgage (the "Mortgage") of even
date herewith from the Borrower to Dyax, which mortgage grants a lien on Unit
228 at the Brimmer Street Garage Condominium, Boston, Massachusetts (the "Real
Estate"), all as more particularly described in such mortgage and (ii) a certain
loan and pledge agreement (the "Loan and Pledge Agreement") of even date
herewith granted by the Borrower in favor of Dyax. Dyax by its acceptance
hereof, shall be entitled to the benefits, and subject to the terms, of the
Mortgage and the Loan and Pledge Agreement.

         If the Borrower conveys, transfers, assigns, encumbers, pledges or
otherwise disposes of any legal or beneficial interest in the Real Estate or in
the equity of redemption in the Real Estate or any part thereof without Dyax's
prior written consent, Dyax may, at its option, require immediate payment of the
entire indebtedness evidenced hereby, with accrued interest thereon, if any, as
provided herein.

         The undersigned agrees to pay, upon maturity (by acceleration or
otherwise), costs of collection, including reasonable attorneys' fees.

         No delay or omission on the part of the holder in exercising any right
hereunder shall operate as a waiver of such right or of any other right of such
holder; nor shall any delay, omission or waiver on any occasion be deemed a bar
to or waiver of the same or any other right on any future occasion. The
undersigned and every indorser or guarantor of this note regardless of the time,
order or place of signing waives presentment, demand, protest and notices of
every kind and assents to any one or more extensions or postponements of the
time of payment or any other indulgences, to any substitutions, exchanges or
releases of collateral if at any time there be available to the holder
collateral for this note, and to the additions or releases of any other parties
or persons primarily or secondarily liable.

         All rights and obligations hereunder shall be governed by and construed
in accordance with the law of the Commonwealth of Massachusetts and this note
shall be deemed to be under seal.

                                                 ------------------------------
                                                 Henry E. Blair, individually

                                           13

<PAGE>

                          COOPERATIVE PLEDGE AGREEMENT

      THIS COOPERATIVE PLEDGE AGREEMENT dated as of October 30, 1998 is made by
Henry E. Blair (the "Pledgor"), residing at 275 Mill Way, Barnstable,
Massachusetts 02630, in favor of Dyax Corp ("Dyax"), a Delaware corporation with
its principal place of business at One Kendall Square, Building 600, Cambridge,
Massachusetts 02139.

                              W I T N E S S E T H:

      WHEREAS, Pledgor desires to purchase 152 shares of Common Stock, evidenced
by Certificate No. ____, of 68 Beacon Street, Inc. (the "Company") a
Massachusetts corporation, which shares entitle the owner to lease an apartment
in the building located at 68 Beacon Street, Boston, Massachusetts (the
"Apartment").

      WHEREAS, pursuant to a Loan and Pledge Agreement dated the date hereof
(the "Loan and Pledge Agreement"), Dyax agreed to make a loan (the "Loan") to
the Pledgor on or after the date hereof evidenced by a promissory note of the
Pledgor in the original principal amount of $600,000 (the "Note") to finance the
acquisition of the shares; and

      WHEREAS, pursuant to the terms of the Loan and Pledge Agreement, the
Pledgor is required to execute and deliver this Agreement and grant the security
interest hereinafter described;

      NOW, THEREFORE, in consideration of the willingness of Dyax to make the
Loan to the Pledgor, and for other good and valuable consideration, receipt of
which is hereby acknowledged, it is hereby agreed as follows:

      1. Security Interest. The Pledgor hereby deposits with and pledges to Dyax
all of the shares of capital stock of the Company (the "Pledged Stock") (the
Pledged Stock and any additional securities or collateral pledged hereunder are
sometimes herein referred to collectively as the "Pledged Collateral"), and the
Pledgor hereby grants to Dyax a security interest in all of the Pledged
Collateral as security for the due and punctual payment performance of the
secured obligations described in section 2 hereof.

      2. Secured Obligations. The security interest hereby granted shall secure
the due and punctual payment and performance of the following liabilities and
obligations of the Pledgor (herein called the "Secured Obligations"):

      (a) Principal of and premium, if any, and interest on the Note;

            (b) All costs and expenses incurred by Dyax in the collection of any
of the Secured Obligations, including without limitation reasonable attorneys'
fees and legal expenses; and

            (c) all future advances made by Dyax for the protection or
preservation of the Pledged Collateral or any portion thereof.

      3. Representations of the Pledgor. The Pledgor hereby represents, warrants
and covenants as follows:

                                       14
<PAGE>

            (a) The Pledgor has the full power, authority and legal right to
enter into this Agreement to be bound hereby and to perform and observe the
terms and conditions hereof, and is in compliance with all applicable material
laws, rules and regulations.

            (b) This Agreement has been duly executed and delivered by the
Pledgor and constitutes the legal, valid and binding obligation of the Pledgor
enforceable against him in accordance with its terms, subject, as to the
enforcement of remedies, to applicable bankruptcy, reorganization, insolvency
and similar laws affecting creditors' rights generally and to moratorium laws
from time to time in effect and to general principles of equity.

            (c) The Pledged Stock consists of not fewer than 152 shares of
Common Stock, evidenced by Certificate No. ____, of the Company.

            (d) The Pledgor as of the date hereof has a net worth, defined as
the fair market value of total assets, exclusive of assets subject to contingent
liabilities, less total liabilities, of at least $10,000,000.

      4. Covenants of the Pledgor. The Pledgor shall

            (a) if the Pledged Collateral is in the form of a certificated
security, within the meaning of the Uniform Commercial Code, as adopted in the
Commonwealth of Massachusetts (the "Code"), surrender possession of the Pledged
Collateral to Dyax;

            (b) if the Pledged Collateral is in the form of an uncertificated
security, within the meaning of the Code, cause the Company to record this
pledge in the records of the Company relating to the Pledged Stock;

            (c) execute all such instruments, documents, and papers, and will do
all such acts as Dyax may reasonably request now and from time to time hereafter
with respect to the perfection of the security interest granted herein and the
assignment effected hereby, including without limitation making payments of the
proceeds of the Loan and such additional amounts as are necessary to cause the
current pledgee of the certificates for the Pledged Stock to deliver such
certificates to Dyax;

            (d) deliver to Dyax, if and when received by the Borrower, any item
representing or constituting any of the Pledged Collateral or, except as
otherwise provided herein, proceeds of Pledged Collateral;

            (f) not cause or permit any of the Pledged Collateral presently
evidenced by a written certificate to be converted to uncertificated securities,
except on request of Dyax;

            (g) not exercise any right with respect to the Pledged Collateral
which would dilute or otherwise adversely affect Dyax's rights to the Pledged
Collateral;

            (h) make a payment on the Loan or grant to Dyax a security interest
in and to, and assign, pledge and deliver to Dyax certificates representing
additional marketable securities issued to the Borrower, if necessary, in order
to ensure that at all times the value of the Pledged Collateral is not less than
150% of the outstanding principal balance of the Loan;

            (i) deliver to Dyax annually on September 30 a certificate stating
that (i) the Borrower as of the date thereof has a net worth, defined as the
fair market value of total assets, exclusive of assets subject to contingent
liabilities, less total liabilities, of at least $10,000,000 and (ii) the value
of the Pledged Collateral as of the date thereof is not less than 150% of the
outstanding principal balance of the Loan.

                                       15
<PAGE>

      5. Special Warranties and Covenants of the Pledgor. The Pledgor hereby
represents, warrants and covenants to Dyax that, except for the lien of the
Company pursuant to a certain Proprietary Lease and as set forth in the Addendum
annexed hereto and made a part hereof:

(a)   The Pledged Collateral is duly and validly pledged with Dyax in accordance
      with law, and the Pledgor warrants and will defend Dyax's right, title and
      security interest in and to the Pledged Collateral against the claims and
      demands of all persons whomsoever.

(b)   The Pledgor has good title to the Pledged Collateral, free and clear of
      all claims, mortgages, pledges, liens, security interests and other
      encumbrances of every nature whatsoever.

(c)   All of the Pledged Stock has been duly and validly issued and is fully
      paid and nonassessable.

(d)   The execution, delivery and performance by the Pledgor of this Agreement
      does not and will not (i) violate or constitute a default under any
      provision of any agreement, note or instrument which is binding upon the
      Pledgor or by which his properties are bound or materially affected, or
      any law, rule or regulation, order writ, injunction or decree of any court
      or governmental instrumentality or any contractual restriction binding on
      the Pledgor, or (ii) require any filing with or consent or other act by or
      in respect of any governmental authority or other person or entity (other
      than the filing of the appropriate number of UCC-1 financing statements
      covering the Pledged Stock, if necessary, and any consent obtained by the
      Pledgor prior to the date hereof) or (iii) constitute a default thereunder
      or result in the imposition or require the creation of any lien or charge
      (other than those created, continued or otherwise contemplated hereby)
      upon the assets of the Pledgor.

(e)   The Pledgor will not sell, convey or otherwise dispose of any of the
      Pledged Collateral, nor will the Pledgor create, incur or permit to exist
      any pledge, mortgage, lien, charge, encumbrance or any security interest
      whatsoever with respect to any of the Pledged Collateral or the proceeds
      thereof, other than liens on and security interests in Pledged Collateral
      created hereby.

(f)   The Pledgor will not consent to or approve the issuance of any additional
      shares of capital stock of any class of the Company.

      6. Distributions. In case, upon the dissolution, winding up, liquidation
or reorganization of the Company whether in bankruptcy, insolvency or
receivership proceedings or upon an assignment for the benefit of creditors or
any other marshalling of the assets and liabilities of the Company or otherwise,
any sum shall be paid or any property shall be distributed upon or with respect
to any of the Pledged Collateral, such sum (less the amounts due to the Company,
if any) shall be paid over to Dyax to be held as collateral security for the
Secured Obligations. In case any stock dividend shall be declared on any of the
Pledged Collateral, or any share of stock or fraction thereof shall be issued
pursuant to any stock split involving any of the Pledged Collateral, or any
distribution of capital (excluding ordinary cash dividends) shall be made on any
of the Pledged Collateral, or any property shall be distributed

                                       16
<PAGE>

upon or with respect to the Pledged Collateral pursuant to recapitalization or
reclassification of the capital of the Company, the shares or other property so
distributed shall be delivered to Dyax to be held as collateral security for the
Secured Obligations.

      7. Events of Default. There shall exist a default under this Agreement
upon the happening of any default (herein called "Events of Default") in the due
and punctual payment of any principal of or premium, if any, or interest on the
Secured Obligations as and when the same shall become due and payable (whether
at maturity or at a date fixed for any prepayment or installment or by
declaration or acceleration or otherwise) or a breach of any covenant contained
in this Agreement or in the leasehold mortgage on the apartment given to secure
the Note and such default shall continue beyond the expiration of the applicable
period of grace, if any.

      8. Rights and Remedies of Dyax. Upon the occurrence of any Event of
Default, such default not having previously been remedied or cured, Dyax shall
have the following rights and remedies, subject to the Addendum attached hereto:

(a)   All rights and remedies provided by law, including, without limitation,
      those provided by the Uniform Commercial Code;

(b)   All rights and remedies provided in this Agreement; and

(c)   All rights and remedies provided in the Note, the leasehold mortgage, this
      Agreement, or in any other agreement, document or instrument pertaining to
      the Secured Obligations.

      9. Right to Transfer into Name of Dyax, etc. Notwithstanding anything to
the contrary contained herein, Dyax will not, unless Dyax shall have purchased
such Pledged Collateral at public or private sale or disposition thereof, (i)
cause any or all of the Pledged Collateral to be transferred into its name or
into the name of its nominee or (ii) exercise the voting power with respect to
any Pledged Collateral. Except as provided in the preceding sentence of this
section 9, the Pledgor shall be entitled to exercise as the Pledgor shall deem
fit, but in a manner not inconsistent with the terms hereof or of the Secured
Obligations, the voting power with respect to the Pledged Collateral.

      10. Right of Dyax to Exercise Rights of Payment, etc. Subject to the
Addendum attached hereto, in case there shall exist an Event of Default, Dyax
shall be entitled to receive and retain, as collateral security for the Secured
Obligation, any and all dividends or other distributions at any time and from
time to time declared or made upon any of the Pledged Collateral, and to
exercise any and all rights of payment, conversion, exchange, subscription or
any other rights, privileges or options pertaining to the Pledged Collateral as
if it were the absolute owner thereof, including without limitation, the right
to exchange, at its discretion, any and all of the Pledged Collateral upon the
merger, consolidation, reorganization, recapitalization or other readjustment of
the Company or, upon the exercise of any such right, privilege or option
pertaining to the Pledged Collateral, and in connection therewith, to deposit
and deliver any and of the Pledged Collateral with any committee, depositary,
transfer registrar or other designated agency upon such terms and conditions as
Dyax may determine, all without liability except to account for property
actually received, but Dyax shall have a duty to exercise any of the

                                       17
<PAGE>

aforesaid rights, privileges or options and shall not be responsible for any
failure to do so or delay in so doing.

      11. Right of Dyax to Dispose of Collateral, etc. Upon the occurrence of an
Event of Default, such default not having previously been remedied or cured,
Dyax shall have the right at any time or times thereafter to sell, resell,
assign and deliver the Pledged Collateral in a single parcel at any exchange or
broker's board or at public or private sale. Unless the Pledged Collateral is
perishable or threatens to decline speedily in value or is of a type customarily
sold on a recognized market, Dyax will give the Pledgor at least twenty-one (21)
days prior written notice at the address of the pledgor specified in section 18
hereof, of the time and place of any public sale thereof or of the time after
which any private sale or any other intended disposition thereof is to be made.
Any such notice shall be deemed to meet any requirement hereunder or under any
applicable law (including the Uniform Commercial Code) that reasonable
notification be given of the time and place of such sale or other disposition.
Such notice may be given without any demand of performance or other demand, all
such demands being hereby expressly waived by the Pledgor. Such written notice
also will be given to the Company at least twenty-one (21) days prior to the
sale or other intended disposition. All such sales shall be at such commercially
reasonable price as Dyax shall deem best and either for cash or on credit or for
future delivery (without assuming any responsibility for credit risk). At any
such sale Dyax may purchase the Pledged Collateral to be sold thereat upon such
terms as Dyax may deem best. Upon any such sale the Pledged Collateral so
purchased shall be held by the purchaser, subject to the Addendum attached
hereto, but absolutely free from any other claims or rights of whatsoever kind
or nature, including any equity of redemption and any similar rights, all such
equity of redemption and any similar rights being hereby expressly waived and
released by the Pledgor. In the event any consent, approval or authorization of
any governmental agency will be necessary to effectuate any such sale, the
Pledgor shall execute, and hereby agrees to cause the Company to execute, all
such applications or other instruments as may be required. The proceeds of any
such sale, together with any other additional collateral security at the time
received and held hereunder, shall be received and applied: first, to all
amounts due to the Company; second, to the payment of all costs, and expenses of
such sale, including reasonable attorneys' fees; third, to the payment of the
Secured Obligations in such order of priority as Dyax shall determine, and any
surplus thereafter remaining shall be to the Pledgor or to whomever may be
legally entitled thereto including, if applicable, any subordinated creditor of
the Company or the Pledgor).

      The Pledgor recognizes that Dyax may be unable to effect a public sale of
the Pledged Collateral by reason of certain prohibitions contained in the
Securities Act of 1933, but may be compelled to resort to one or more private
sales to a restricted group of purchasers, each of whom will be obligated to
agree, among other things, to acquire such Pledged Collateral for its own
account, for investment and not with a view to the distribution or resale
thereof. The Pledgor acknowledges that private sales so made may be at prices
and upon other terms less favorable seller than if such Pledged Collateral were
sold at public sales, and that Dyax has no obligation to delay sale of any such
Pledged Collateral for the period of time necessary to permit such Pledged
Collateral to be registered for public sales under the Securities Act of 1933.
The Pledgor agrees that any such private sales shall not be deemed to have been
made in a commercially unreasonable mariner solely because they shall have been
made under the foregoing circumstances.

                                       18
<PAGE>

      12. Collection of Amounts Payable on Account of Pledged Collateral, etc.
Upon the occurrence of any Event of Default, Dyax may, but without obligation to
do so, demand, sue for and/or collect any money or property at any time due,
payable or receivable, to which it may be entitled hereunder, on account of or
in exchange for any of the Pledged Collateral and shall have the right, for and
in the name, place and stead of the Pledgor, to execute endorsements,
assignments or other instruments of conveyance or transfer with respect to all
or any of the Pledged Collateral.

      13. Care of Pledged Collateral in Dyax's Possession. Beyond the exercise
of reasonable care to assure the safe custody of the Pledged Collateral while
held hereunder, Dyax shall have no duty or liability to collect any sums due in
respect thereof or to protect or preserve rights pertaining thereto, and shall
be relieved of all responsibility for the Pledged Collateral upon surrendering
the same to the Pledgor.

      14. Waivers, etc. The Pledgor hereby waives presentment, demand, notice,
protest and, except as is otherwise provided herein, all other demands and
notices in connection with this Agreement or the enforcement of Dyax's rights
hereunder or in connection with the Secured Obligations or any Pledged
Collateral; consents to and waives notice of the granting of renewals,
extensions of time for payment or other indulgences to the Company or the
Pledgor or to any third party, or substitution, release or surrender of any
collateral security for the Secured Obligation, the addition or release of
persons primarily or secondarily liable on the Secured Obligation or on any
collateral security for the Secured Obligation, the acceptance of partial
payments on any Secured Obligation or on any collateral security for the Secured
Obligation and/or the settlement or compromise thereof. No delay or omission on
the part of Dyax in exercising any right hereunder shall operate as a waiver of
such right or of any other right no waiver by Dyax or by any other holder of the
Secured Obligations of any default shall be effective unless in writing nor
operate rate as a waiver of any other default or of the same default on a future
occasion. The Pledgor further waives any right it may have under the
constitution of the Commonwealth of Massachusetts or under the Constitution of
the United States of America, to notice (other than any requirement of notice
provided herein) or to a judicial hearing prior to exercise of any right or
remedy provided by this Agreement to Dyax and waives its rights, if any, to set
aside or invalidate any sale duly consummated in accordance with the foregoing
provisions on the grounds (if such be the case) that the sale was consummated
without a prior judicial hearing. The Pledgor's waivers under this section have
been made voluntarily, intelligently and knowingly and after the Pledgor has
been apprised and counseled by its attorneys as to the nature thereof and its
possible alternative rights.

      15. Termination; Assignment, etc. This Agreement and the security interest
in the Pledged Collateral created hereby shall terminate when all the Secured
Obligations have been paid and finally discharged in full. No waiver by Dyax or
by any other holder of the Secured obligation of any default shall be effective
unless in writing nor operate as a waiver of any other default or of the same
default on a future occasion. In the event of a sale or assignment by Dyax of
the Secured obligation held by it, Dyax may assign or transfer its rights and
interest under this Agreement in whole to the purchaser or purchasers of such
Secured Obligations, whereupon such purchaser or purchasers shall become vested
with all of the powers and rights of Dyax hereunder, and Dyax shall thereafter
be forever released and fully discharged from any liability or responsibility
hereunder with respect to the rights and interest so assigned.

                                       19
<PAGE>

      16. Reinstatement. Notwithstanding the provisions of section 15, this
Agreement shall continue to be effective or be reinstated, as the case may be,
if at any time any amount received by Dyax in respect of the Secured Obligations
is rescinded or must otherwise be restored or returned by Dyax upon the
insolvency, bankruptcy, dissolution, liquidation or reorganization of the
Company or the Pledgor or upon the appointment of any intervenor or conservator
of, or trustee or similar official for, the Company or the Pledgor or any
substantial part of their respective properties, or otherwise, all as though
such payments had not been made.

      17. Restrictions on Transfer. Notwithstanding any provision in this
Agreement, any sale, assignment, conveyance, or transfer of any kind or nature
shall be subject to the Mortgage Loans, Cooperative Documents and Recognition
Agreement identified in the Addendum annexed hereto and made part hereof.

      18. Notices. Except as otherwise provided herein, all notices to the
Pledgor, the Company or to Dyax shall be in writing and shall be deemed to have
been sufficiently given or served for all purposed hereof if personally
delivered or mailed by certified mail, return receipt requested, postage
prepaid, as follows:

      (a)   if to the Pledgor:

                  Henry E. Blair
                  Unit 7E
                  68 Beacon Street
                  Boston, MA 02108

      (b)   if to Dyax:

                  Dyax Corp.
                  One Kendall Square, Building 600
                  Cambridge, MA     02139

                                       20
<PAGE>

      (c)   if to the Company:

                  68 Beacon Street, Inc.
                  c/o John Cupuano
                  R.M. Bradley
                  250 Boylston Street, 4th Floor
                  Boston, MA 02116

or at such other address as the party to whom such notice is directed may have
designated in writing to the other party hereto.

      19. Miscellaneous. This Agreement shall be binding upon Dyax and his
representatives, successors and assigns, and inure to the benefit of Dyax and
its successors and assigns, and the term "Dyax" shall be deemed to include any
other holder or holders of the Secured Obligations. In case any provision in
this Agreement shall be invalid, illegal or unenforceable, the validity,
legality and enforceability of the remaining provisions shall not in any way be
affected or impaired thereby.

      20. Governing Law; Jurisdiction; Waiver of Jury Trial. This Agreement,
including the validity hereof and the rights and obligations of the parties
hereunder, shall be construed in accordance with and governed by the laws of the
Commonwealth of Massachusetts. The Pledgor, to the extent that he may lawfully
do so, hereby consents to service of process, and to be sued, in the
Commonwealth of Massachusetts and the United States District Court for the
District of Massachusetts, as well as to the jurisdiction of all courts to which
an appeal may be taken from such courts, for the purpose of any suit, action or
other proceeding arising out of any of its obligations hereunder or with respect
to the transactions contemplated hereby, and expressly waives any and all
objections it may have as to venue in any such courts. The Pledgor further
agrees that a summons and complaint commencing an action or proceeding in any of
such courts shall be properly served and shall confer personal jurisdiction if
served personally or by certified mail to it at its address provided in section
18 hereof or as otherwise provided under the laws of the Commonwealth of
Massachusetts. The Pledgor irrevocably waives all right to a trial by jury in
any suit, action or other proceeding instituted by or against the Pledgor in
respect of its obligations hereunder or the transactions contemplated hereby.

      21. Addendum. The provisions of this Agreement are modified by an Addendum
annexed hereto and made a part hereof. In the event of any inconsistency between
the provisions of this Agreement and the Addendum, the provisions of the
Addendum and the documents referenced therein shall control.

                                       21
<PAGE>

      IN WITNESS WHEREOF, the undersigned has executed this Agreement as a
sealed instrument as of the date first above written.

                                    /s/ Henry E. Blair
                                    ------------------------------
                                    Henry E. Blair, Individually

                                       22
<PAGE>

                    ADDENDUM TO PLEDGE AND ASSIGNMENT BETWEEN
                          Henry E. Blair and Dyax Corp.

      All of Dyax's rights in and to said shares and lease, as hereinafter set
forth, are subject to the rights and priorities of 68 Beacon Street, Inc. as set
forth in its Articles of Incorporation, as amended, By-Laws, Rules and
Regulations and Proprietary Lease (the "Cooperative Documents") and the
Recognition Agreement of even date executed in connection herewith. The
presently existing provisions of such documents will control in the event of any
conflict between those provisions and the provisions herein.

      Dated: October 30, 1998

                                    /s/ Henry E. Blair
                                    -------------------------------
                                    Henry E. Blair, Individually<PAGE>
                                                                   EXHIBIT 10.11

            NEITHER THIS SECURITY NOR THE SECURITIES INTO WHICH IT IS
       CONVERTIBLE HAVE BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933,
     AS AMENDED (THE "ACT"), OR APPLICABLE STATE SECURITIES LAWS AND NEITHER
    MAY BE TRANSFERRED OR OTHERWISE DISPOSED OF UNLESS SUCH SECURITY HAS BEEN
                  REGISTERED UNDER THE ACT AND SUCH LAWS OR (1)
           REGISTRATION UNDER APPLICABLE STATE SECURITIES LAWS IS NOT
         REQUIRED AND (2) AN OPINION OF COUNSEL SATISFACTORY TO MAKER IS
        FURNISHED TO MAKER TO THE EFFECT THAT REGISTRATION UNDER THE ACT
                                IS NOT REQUIRED.

                          SECURED CONVERTIBLE TERM NOTE

                                                       Charlottesville, Virginia

$500,000                                                         August 11, 1995

            FOR VALUE RECEIVED, Biotage, Inc., a Delaware corporation (the
"Maker"), hereby promises to pay to Sheridan G. Snyder (hereinafter referred to
as the "Holder"), or registered assigns, on or before the Maturity Date (as
hereinafter defined), as set forth herein, the principal amount of Five Hundred
Thousand Dollars ($500,000), or such part thereof as then remains unpaid,
together with interest from the date hereof on the unpaid principal balance of
this Note from time to time outstanding at a rate of interest equal to the Prime
Rate (as hereinafter defined) plus one percent (1%) per annum for the period
beginning on the date hereof and continuing for the remainder of the term
hereof. Interest shall accrue from and after the date hereof, and shall be
payable on the last day of each month commencing on August 31, 1995 and
continuing monthly thereafter until maturity. As used herein, (i) the "Maturity
Date" shall mean the earliest to occur of (a) the date of closing by Maker of a
firm commitment underwritten public offering pursuant to an effective
registration statement under the Securities Act of 1933, as amended (the
"Securities Act"), covering the offer and sale of shares of common stock for the
account of Maker at a price per share of not less than $6.00 (subject to
equitable adjustment in the event of any stock split, stock dividend,
combination, reorganization, reclassification or other similar event) and which
results in proceeds to Maker, net of commissions and discounts, of not less than
$10,000,000, (b) the fifth anniversary of the date of this Note as set forth
above and (c) an Event of Default (as such term is defined below) and (ii) the
"Prime Rate" shall mean that rate of interest announced or published by Crestar
Bank, Charlottesville, Virginia as being its prime rate of interest, whether or
not such rate is actually charged.

1.    Payment in Cash.

      Principal and interest shall be payable in lawful money of the United
States of America, by check, at the business address of the Holder or at such
other place as the legal Holder may designate from time to time in writing to
Maker. Interest shall be computed on the basis of actual days elapsed over a
365-day year.
<PAGE>

2.    Prepayment.

      Upon ten (10) days prior written notice to the Holder of this Note, Maker
shall have the right, at any time prior to the Maturity Date or conversion of
this Note pursuant to Section 4 hereof, to prepay all of the outstanding
principal amount of this Note, and accrued and unpaid interest thereon, without
premium or penalty, subject to the rights of the Holder of this Note to convert
amounts outstanding under this Note pursuant to Section 4 below at any time
prior to the date specified in such notice for prepayment; provided, however,
that notwithstanding the foregoing, in no event shall any prepayment of
principal be made by Maker with respect to any portion of this Note unless and
until Maker shall have offered to prepay a like proportion of all Notes (as such
term is defined below).

3.    Description of Notes.

      This Note is one of several Notes to be issued by PEC (the "PEC Notes"),
and by Maker (the "Biotage Notes" and, collectively with the PEC Notes, the
"Notes"), of like tenor issued or to be issued as a condition to the
consummation of the transactions contemplated by the Agreement and Plan of
Merger dated as of August 4, 1995 (the "Merger Agreement") by and among Maker
and the parties named therein having an aggregate original principal balance of
$3,130,292.65. This Note is secured pursuant to, and entitled to the benefits of
(including the security described in), a certain Security Agreement dated as of
May 11, 1993 by and between Maker and the Holder (as the same may be amended
from time to time, hereinafter referred to as the "Security Agreement"). The
Holder of this Note, by his acceptance hereof, shall be entitled to the
benefits, and subject to the terms, of the Security Agreement.

4.    Conversion.

      If at any time after the consummation of the transactions contemplated by
the Merger Agreement and prior to the Maturity Date, Maker consummates the offer
and sale of Equity Securities (each, an "Equity Financing"), the Holder shall
have the right at the Holder's option, to convert all or any part of the
principal amount of this Note into such Holder's pro rata share of the Equity
Securities being offered in the Equity Financing at a conversion price equal to
the price per share of the Equity Securities sold in the Equity Financing. As
used herein, the term "Equity Securities" shall mean securities of Maker which
are issued for cash and which are either (i) equity securities or (ii)
securities having rights or options to acquire equity securities, but shall not
include (a) securities issued from time to time by Maker in connection with the
licensing or acquisition by Maker of technology or intellectual property, (b)
securities issued from time to time to employees or consultants of Maker
pursuant to any stock option plan, stock purchase or other equity plan of Maker
approved by a majority of Maker's Board of Directors or (c) shares of Class A
Series 3 Preferred Stock of Maker issued on or before September 30, 1995. The
Holder's pro rata portion of Equity Securities being offered in any Equity
Financing shall equal the result obtained by multiplying (A) twenty five percent
(25%) of the aggregate number of Equity Securities being offered in the Equity
Financing by (B) a fraction, the numerator of which shall be equal to the amount
of principal outstanding under this Note with respect to which the Holder has
exercised conversion rights as provided herein and the denominator of which
shall be equal to the aggregate amount of principal outstanding under all of the
Notes. In the event that the

                                      - 2 -
<PAGE>

Holder shall elect to convert this Note as described in this Section 4, the
Holder shall be subject to all of the terms and conditions applicable to the
purchasers buying the Equity Securities in the Equity Financing.

5.    Mechanics of Conversion.

      Maker shall give the Holder twenty (20) days' prior written notice (the
"Company Notice") of the occurrence of an Equity Financing, which notice shall
set forth the anticipated closing date of the Equity Financing and the Holder's
conversion price with respect thereto. The Holder may exercise its right of
conversion by (i) surrendering this Note duly endorsed at the office of Maker
and (ii) delivering written notice to Maker within ten (10) days of its receipt
of the Company Notice, specifying the principal amount of this Note which the
Holder wishes to be converted and the name or names in which the certificate or
certificates for Equity Securities are to be issued. Maker shall, as soon as
practical following the closing of the Equity Financing, issue and deliver to
the Holder a certificate or certificates for the number of Equity Securities to
which the Holder shall be entitled as aforesaid, together with the payment in
cash of all accrued but unpaid interest on this Note through the closing date of
the Equity Financing; provided, however, that if the person in whose name such
certificate or certificates are requested to be registered is other than the
registered owner of this Note, Maker may require, prior to issuance of a
certificate in the name of such other person, that it receive reasonable
transfer documentation (including opinions) or other evidence that the issuance
of certificates in such other name as requested does not and will not cause a
violation of the Securities Act, any similar Federal statute at the time in
effect or any applicable state securities laws. Such conversion shall be deemed
to have been made on the closing date of the Equity Financing, and the person or
persons entitled to receive the shares of stock issuable upon such conversion
shall be treated for all purposes as the record holder or holders of such shares
as of such date. If less than the entire outstanding principal amount of this
Note is being converted, a new Note shall be delivered to the Holder for the
unconverted principal balance and shall be of a like tenor as to all terms as
this Note.

6.    Securities Act.

      Upon conversion of this Note, the registered Holder will be required to
execute and deliver to Maker an instrument, in form satisfactory to Maker,
representing that the Equity Securities issuable upon conversion hereof are
being acquired for investment and not with a view to distribution within the
meaning of the Securities Act.

7.    No Fractional Shares and Certificates.

      No fractional shares shall be issued upon conversion of this Note and the
number of shares of Equity Securities to be issued shall be rounded down to the
nearest whole share and the Holder shall be entitled to receive in cash an
amount equal to the conversion price then in effect multiplied by the fractional
share.

                                      - 3 -
<PAGE>

8.    Events of Default.

      If any Event of Default (as defined in the Security Agreement) shall occur
and be continuing, then any Holder of this Note may, by notice to Maker, declare
the entire unpaid principal amount of this Note, and all interest accrued and
unpaid hereon to be forthwith due and payable, whereupon the Note and all such
accrued interest shall become and be forthwith due and payable.

9.    Note Register.

            (a) Maker shall keep at its principal executive offices a register
(herein sometimes referred to as the "Note Register"), in which, subject to such
reasonable regulations as it may prescribe, but at its expense (other than
transfer taxes, if any), Maker shall provide for the registration and transfer
of this Note. The person or entity in whose name any registered Note shall be
registered shall be deemed and treated as the owner and holder hereof for all
purposes hereunder.

            (b) Whenever this Note shall be surrendered at the principal
executive office of Maker for transfer or exchange, accompanied by a written
instrument of transfer in form reasonably satisfactory to Maker duly executed by
the Holder hereof or its attorney duly authorized in writing, Maker shall
execute and deliver in exchange therefor a new note or notes, as may be
requested by such Holder, in the same aggregate unpaid principal amount and
payable on the same terms as the principal amount of the note or notes so
surrendered; each such new Note shall be dated as of the date to which interest
has been paid on the unpaid principal amount of the note or notes so surrendered
and shall be in such principal amount and registered in such name or names as
such Holder may designate in writing; provided, however, that if the person in
whose name a Note is requested to be registered is other than the registered
owner of this Note, Maker may require, prior to issuance of a Note in the name
of such other person, that it receive reasonable transfer documentation
(including opinions) or other evidence that the issuance of a Note in such other
name as requested does not and will not cause a violation of the Securities Act,
any similar Federal statute at the time in effect or any applicable state
securities laws.

            (c) Upon receipt by Maker of evidence reasonably satisfactory to it
of the loss, theft, destruction or mutilation of this Note and of indemnity
reasonably satisfactory to it, and upon reimbursement to Maker of all reasonable
expenses incidental thereto, and upon surrender and cancellation of this Note
(in case of mutilation), Maker will make and deliver in lieu of this Note a new
Note of like tenor and unpaid principal amount and dated as of the date to which
interest has been paid on the unpaid principal amount of this Note in lieu of
which such new Note is made and delivered.

10.   General.

            (a) Governing Law. This Note shall be governed by and construed in
accordance with the law of the Commonwealth of Virginia, excluding the body of
law relating to conflict of laws. Notwithstanding anything to the contrary
contained herein, in no

                                      - 4 -
<PAGE>

event may the effective rate of interest collected or received by the Holder
exceed that which may be charged, collected or received by the Holder under
applicable law.

            (b) Interpretation. If any term or provision of this Note shall be
held invalid, illegal or unenforceable, the validity of all other terms and
provisions hereof shall in no way be affected thereby.

            (c) Amendment. The terms of this Note and the other Notes may be
amended or waiver of compliance of any term hereof or thereof may be obtained by
Maker with the written consent of holders of greater than sixty-six and
two-thirds percent (66 2/3%) of the unpaid aggregate principal amount of all of
the Notes outstanding at the time of the amendment or waiver, whether or not the
Holder hereof shall agree to such amendment or waiver; provided, however, that
no such amendment or waiver shall be effective to reduce the principal amount
hereof or the rate of interest payable hereunder or to otherwise provide terms
herein more favorable to the Holder than the terms provided in the other Notes.

            (d) Successors and Assigns; Transferability. This Note shall be
binding upon Maker and its successors and assigns and shall inure to the benefit
of the Holder and its successors and permitted assigns (which shall include
permitted transferees). This Note or any interest therein may not be assigned
except in accordance with the terms hereof.

            (e) Notices. All notices, requests, consents and demands shall be
made in writing and shall be mailed postage prepaid, or delivered by hand, to
Maker or to the Holder thereof at their respective addresses set forth below or
to such other address as may be furnished in writing to the other party hereto:

                  If to the Holder:       At the address shown below.

                  If to Maker:            Biotage, Inc.
                                          1500 Avon Street Ext.
                                          Charlottesville, VA 22901
                                          Attention: President

All notices, requests, consents and other communications hereunder shall be
deemed to have been given either (i) if by hand, at the time of the delivery
thereof to the receiving party at the address of such party set forth above,
(ii) if made by telex, telecopy or facsimile transmission, at the time that
receipt thereof has been acknowledged by electronic confirmation or otherwise,
(iii) if sent by overnight courier, on the next business day following the day
such notice is delivered to the courier service, or (iv) if sent by registered
or certified mail, on the 5th business day following the day such mailing is
made.

            (f) Saturdays, Sundays, Holidays. If any date that may at any time
be specified in this Note as a date for the making of any payment of interest
under this Note shall fall on Saturday, Sunday or on a day which in Virginia
shall be a legal holiday, then the date for the making of that payment shall be
the next subsequent day which is not a Saturday, Sunday or legal holiday.

                                      - 5 -
<PAGE>

      IN WITNESS WHEREOF, the undersigned has executed this Note as of the date
first above written.

                                    BIOTAGE, INC.

                                       By: /s/ Robert Dishman
                                           --------------------------
                                       Title:  President

Name of Holder:         Sheridan Snyder

Address of Holder:      Sheridan G. Snyder
                        Route 1
                        Box 117
                        Afton, VA 22920

                                      - 6 -
<PAGE>

                              SECURITY AGREEMENT

      THIS AGREEMENT is made as of May 11, 1993, between BIOTAGE, INC., a
Delaware corporation (the "Debtor") and SHERIDAN G. SNYDER (the "Secured
Party").

                                   Recitals

      A. The Secured Party has agreed to extend a line of credit to the Debtor
in the principal sum of up to $500,000.00 plus interest.

      B. The Secured Party is willing to make advances under the line of credit,
but only upon the condition, among others, that the Debtor execute and deliver
this Agreement.

      NOW, THEREFORE, in consideration of the foregoing Recitals and the mutual
covenants herein contained and for other good and valuable consideration, the
receipt and sufficiency of which are hereby acknowledged, the parties agrees as
follows:

SECTION 1. -- DEFINED TERMS

      The following terms used herein shall have the following meanings unless
the context otherwise requires:

      Accounts. All accounts as defined in the Uniform Commercial Code, whether
now owned or hereafter acquired by Debtor, and all proceeds and products
thereof.

      Collateral. All Accounts, Equipment, Intellectual Property and Inventory
provided as security under this Agreement.

      Equipment. All of the Debtor's furniture, fixtures and equipment,
including all equipment as defined in the Uniform Commercial Code, and
including, but not limited to, any leases, rental agreements, chattel paper,
rental payments and insurance proceeds together with all accessories,
accessions, attachments, parts, replacements, substitutions, improvements,
repairs installed in or affixed to any equipment, whether now or owned or
hereafter acquired by Debtor, and all proceeds and products thereof.

      Intellectual Property. All patents, patent applications, trademark,
tradenames, copyrights, technology, know-how, processes, computer programs,
databases, systems and software, and other intellectual and proprietary rights,
including all contract rights and licenses with respect thereto, together with
all good will associated therewith whether now owned or hereafter acquired by
the Debtor including, but not limited to, all of the Debtor's right, title and
interest in and to the Debtor's license (the "Patent License") of United States
Patent No. 4,250,035 issued February 10, 1981, entitled "Radial Compression of
Packed Beds", and all reissues, continuations and extensions thereof, as well as
all foreign patents and patent applications corresponding thereto.

                                      - 7 -
<PAGE>

      Inventory. All goods and personal property of every nature which are held
for sale or furnished or are to be furnished under contracts of service or sale
or lease, supplies, stock-in-trade, all raw materials, work-in-process, finished
goods, and all returned, reclaimed and repossessed goods, whether now in the
Debtor's possession or control, in transit, in storage, or hereafter acquired by
way of replacement, substitutions, addition or otherwise and all other inventory
as defined in the Uniform Commercial Code, whether now owned or hereafter
acquired by Debtor, and all proceeds and products thereof.

      Obligations. All indebtedness of the Debtor to the Secured Party evidence
by a Credit Line Note of even date made by Debtor payable to the Secured Party
in the principal sum of up to $500,000.00, including all renewals, extensions
and modifications thereof, and the agreements and warranties of the Debtor
contained in this Agreement.

SECTION 2. --  COLLATERAL.

      2.1. Security Agreement. As Collateral to secure the prompt payment and
performance of the Obligations, the Debtor hereby grants to the Secured Party a
security interest in the Accounts, the Equipment, the Intellectual Property and
the Inventory, including all proceeds of any of the foregoing. Debtor will not
sell, assign, encumber or otherwise transfer the Collateral or the proceeds
therefrom other than to the Secured Party or in the ordinary course of Debtor's
business without the prior written consent of the Secured Party. Upon request of
the Secured Party, Debtor shall promptly perform all acts reasonably necessary
to further evidence or perfect the security interest of the Secured Party in the
Collateral and to obtain for the Secured Party the benefits of a secured party
under the laws of the State of Virginia.

      2.2. Consent of Licensor. The Debtor shall, upon execution and delivery of
this Agreement, use its best efforts to obtain the consent of the Licensor under
the Patent License to the grant of the foregoing security interest, which
consent shall be substantially in the form of Exhibit A hereto.

SECTION 3. -- REPRESENTATIONS

      The Debtor represents and warrants to the Secured Party, and such
representations and warranties shall be continuing so long as any Obligations
shall remain outstanding as follows:

      3.1. Due Authorization. The Debtor has the power and authority to enter
into this Agreement and perform its obligations hereunder and by proper action
has duly authorized the execution and delivery of this Agreement and the
performance of its obligations hereunder.

      3.2. Binding Agreement. This Agreement constitutes the valid and legally
binding obligation of the Debtor, enforceable in accordance with its terms.

                                      - 8 -
<PAGE>

      3.3. Ownership of Collateral. (a) Debtor now owns, or will use the
advances secured hereby to become the owner of, the Collateral and will have the
right to grant to the Secured Party a security interest therein.

            (b) The Debtor owns, or is licensed to use, all Intellectual
Property necessary for the conduct of its business. As of the date hereof, no
material claim has been asserted and it pending by any person or entity with
respect to the use by the Debtor of any Intellectual Property or challenging or
questioning the validity or effectiveness of any Intellectual Property necessary
for the conduct of the Debtor's business.

      3.4. Location of Collateral. The Collateral and all records relating
thereto are located at 1500 Avon Street Extended, Charlottesville, Virginia
22901. The Debtor will not change the location of the Collateral or any part
thereof, without giving the Secured Party at least 30 days' prior written
notice.

      3.5. Collateral Free of Encumbrances. The Debtor has not previously
assigned, mortgaged, or encumbered any Collateral, and the Collateral is not
subject to a prior security interest or lien in favor of any person other than
the Secured Party. The Debtor will defend the Collateral against all claims and
demands of all persons at any time claiming any interest therein.

      3.6. Setoffs, Counterclaims and Defenses to Accounts. The Accounts hereby
assigned are valid obligations, correct in amount, do not arise from or relate
to the sale of farm products by a farmer, and there are no set offs,
counterclaims or defenses of any kind thereto. The Debtor will immediately
notify the Secured Party of any account to which such representations are
untrue.

SECTION 4. -- COVENANTS

      The Debtor covenants and agrees that so long as any of the Obligations
remain outstanding:

      4.1. Financing Statements. The Debtor will execute financing statements
and continuation statements in form satisfactory to the Secured Party and the
Debtor will reimburse the Secured Party for all expenses incurred in the filing
of financing statements, continuation statements and termination statements. The
Debtor agrees the Secured Party may file a carbon, photographic copy or other
reproduction of any financing statement.

      4.2. Maintenance of Records. The Debtor will keep and maintain, at its own
cost and expense, satisfactory, complete and current records of the Collateral,
including, but not limited to, all shipments received, deliveries made,
contracts performed, payments received, credits granted thereon and other
dealings therewith. Upon request by the Secured Party, the Debtor will provide
it with written reports of the status of the Collateral, or any part thereof, as
of the period specified. These reports shall be in such form and in such detail
as the Secured Party shall reasonably direct. The Debtor will not change the
location of its books and records without giving the Secured Party at least
thirty (30) days' prior written notice. The Debtor will protect its records
against fire, theft, loss or any other manner of destruction or loss.

      4.3. Taxes. The Debtor will pay promptly when due all taxes, charges and
assessments, including penalties and interest, which are or may become a lien on
the

                                      - 9 -
<PAGE>

Collateral or any part thereof, except to the extent that they may be contested
in good faith and by appropriate proceedings.

      4.4. Change of Name, Residence, Place of Business. The Debtor will not
change its name, operate under any assumed name or change its residence,
corporate structure or principal place of business, without giving the Secured
Party at least thirty (30) days' prior written notice.

      4.5. Inspection of Books and Records. The Secured Party, or its agents,
may at any time, and from time to time, inspect the Collateral and the books and
records of the Debtor pertaining to the Collateral. It is specifically agreed
that the Secured Party shall have, and the Debtor hereby grants to the Secured
Party, a security interest in all books of accounts and records (including
computer software) of the Debtor and shall have access to them at any time for
inspection, verification, examination and audit. If requested by the Secured
Party, the Debtor will stamp all chattel paper hereby assigned in a form and
manner satisfactory to the Secured Party with an appropriate reference to the
effect that the chattel paper has been assigned to the Secured Party, and the
Debtor will similarly stamp its account ledgers and other books and records
pertaining to the assigned Accounts.

      4.6. Expenses. The Debtor shall be liable for, and agrees to pay the
Secured Party any and all expenses incurred or paid by the Secured Party in
protecting or enforcing its rights under this Agreement, including reasonable
attorney's fees, whether incurred in collecting specific Accounts or otherwise.
At its option, the Secured Party may discharge taxes, liens, security interests
or other encumbrances on the Collateral. The Debtor agrees to reimburse the
Secured Party on demand for any payments so made, and until such reimbursement,
the amount of any such payment, with interest at the rate provided for in the
Obligations from date of payment until reimbursement, shall be added to the
indebtedness owed by the Debtor and shall be secured by this Security Agreement.

      4.7. Insurance. The Debtor will continuously insure the Collateral with a
responsible company or companies satisfactory to the bank against fire with
extended coverage) in the full insurable value of the Collateral and against
such other casualties in such amounts as the Secured Party shall reasonably
require. This insurance policy (or policies) shall have attached thereto a
standard loss payable clause, without contribution, in favor of the Secured
Party, as its interest may appear, and shall otherwise be in form acceptable to
the Secured Party, and the Debtor will use its best efforts to have such policy
(or policies) provided that it (they) may not be cancelled without ten (10)
days' prior written notice to the Secured Party. The Debtor will deliver the
policy or policies, properly endorsed, as additional security, and where a
renewal policy is necessary in the performance of this covenant, the Debtor will
deliver it, as security, at least ten (10) days before the expiration of the
existing insurance. The Debtor hereby assigns to the Secured Party any return of
unearned premiums which may be due upon cancellation of any such policy or
policies for any reason whatsoever and directs the insurer(s) to pay to the
Secured Party any amounts so due. The Debtor hereby irrevocably appoints the
Secured Party as its attorney-in-fact, with full power of substitution to
execute loss claims and other applications for payment of benefits under any
insurance policy in the name of either the Debtor or the Secured Party, receive
all monies and endorse drafts, checks, and other instruments for the

                                     - 10 -
<PAGE>

payment of any proceeds off any insurance or in order to Collect any return of
unearned premiums. This appointment shall be deemed a power coupled with an
interest and shall not be terminable by the Debtor so long as the Debtor remains
indebted to the Secured Party, and shall not terminate on disability or the
Debtor.

      4.8. Compliance with Federal and State Laws. The Debtor will comply wish
all federal and State Laws applicable to its business, whether now in effect or
hereafter enacted, and all statutes and regulations issued by the state or
states in which the Debtor conducts business, and upon request the Debtor will
provide the Secured Party with such evidence of compliance as the Secured Party
may reasonably request.

      4.9. Audit. The Debtor will cause its books to be reviewed at least
annually and will furnish to the Secured Party within ninety (90) days after the
end of its fiscal year financial statements relating to Debtor's operations at
the Facility duly prepared and reviewed by an independent certified public
accountant, including balance sheets and profit and loss statements. The Debtor
will furnish the Secured Party within forty-five (45) days after the close of
each quarter a similar profit and loss statement for, and a balance sheet as of
the end of, such quarter, such statements to be duly certified by the president,
treasurer, or chief accounting officer of the Debtor.

      4.10. Other Loans and Security Interests. If the Debtor obtains any loan
from anyone other than the Secured Party, or if the Debtor obtains an extension
or renewal of any present indebtedness to anyone other than the Secured Party,
except trade indebtedness, the Debtor will notify the Secured Party of such fact
in writing within three (3) days.

      4.11. Qualification to do Business. The Debtor will, at the request of the
Secured Party, qualify to do business and obtain all requisite licenses and
permits in each state in which such action may be necessary in order to maintain
any action to collect any debt.

      4.12. Compromises and Discounts. Without the prior written consent of the
Secured Party, the Debtor will not grant any extension of time in the payment of
any Accounts or compromise, compound or settle the same for less than the full
amount thereof, or release wholly or partially any person liable for payment
thereof, or allow any credit or discount whatsoever in the amount of any Account
as invoiced except for ordinary trade discounts or allowances for prompt
payment. The Debtor, moreover, will not agree to any material modification of
any Account herein assigned (whether specifically listed or not) without the
prior written consent of the Secured Party.

      4.13 Promissory Notes, Trade Acceptances, and Other Instruments. If any of
the Debtor's Accounts are or should become evidenced by chattel paper or
promissory notes, trade acceptances, or other instruments, the Debtor will
promptly notify the Secured Party and upon request by the Secured Party will
immediately deliver the same to the Secured Party, appropriately endorsed or
assigned with recourse to the Secured Party's order, and regardless of the form
of such endorsement or assignment the Debtor hereby waives presentment, demand,
notice of dishonor, protest and notice of protest and all other notices with
respect thereto and agrees to take all necessary steps to preserve rights
against prior parties to instruments and chattel paper.

                                     - 11 -
<PAGE>

      4.13. Collection of Accounts. The Bank hereby authorizes the Debtor to
collect the Accounts, subject to direction and control, but the Secured Party
may, without cause or notice, curtail or terminate said authority at any time.
Upon notice by the Secured Party, whether oral or in writing, to the Debtor, the
Debtor shall forthwith upon receipt of all checks, drafts, cash, and other
remittances in payment of or on account of the Accounts, deposit the same in one
or more special accounts maintained with the Secured Party over which the
Secured Party alone shall have the power of withdrawal. The remittance of the
proceeds of such Accounts shall not, however, constitute payment or liquidation
of such Accounts until the Secured Party shall receive good funds for such
proceeds. Funds placed in such special accounts shall be held by the Secured
Party as security for all obligations secured hereunder. These proceeds shall be
deposited in precisely the form received, except for the endorsement of the
Debtor where necessary to permit collection of items, which endorsement the
Debtor agrees to make, and which endorsement the Secured Party is also hereby
authorized, as attorney-in-fact, to make on behalf of the Debtor. In the event
the Secured Party has notified the Debtor to make deposits to a special account,
pending such deposit, the Debtor agrees that it will not commingle any such
checks, drafts, cash or other remittances with any funds or other property of
the Debtor, but will hold them separate and apart therefrom, and upon an express
trust for the Secured Party until deposit thereof is made in the special
account. The Secured Party will, from time to time, apply the whole or any part
of the Collateral funds on deposit in this special account against such
obligations as is secured hereby as the Secured Party may in its sole discretion
elect. At the sole election of the Secured Party, any portion of said funds on
deposit in the special account which the Secured Party shall elect not to apply
to the Obligations may be paid over by the Secured Party to the Debtor. The
Secured Party, and any officer or agent of the Secured Party, is hereby
constituted and appointed as true and lawful attorney-in-fact of the Debtor with
full power at any time, whether or not the Debtor be in default under this or
any other agreement: (a) to notify any and all account debtors to make payment
directly to the Secured Party and otherwise to notify the account debtors of
this assignment; (b) to ask for, demand, collect, institute and maintain suits
for, receive, compound, compromise and give acquittances for any and all sums
owing, which are now, or may hereafter become, due upon said Accounts, and to
enforce payment thereof either in its name or in the Debtor's name; (c) to
endorse the name of the Debtor on checks, drafts or other items tendered or
received in payment of said Accounts, and (d) to enter upon the premises of the
Debtor at any time for the purpose of reducing to possession the Accounts
(including chattel paper) and all cash or non-cash proceeds thereof, or for the
purpose of inspecting the Inventory and inspecting and/or auditing the books,
records and procedures of the Debtor. This power of attorney is coupled with an
interest and shall be irrevocable as long as any Obligations shall remain
outstanding, and shall not terminate on disability of the Debtor.

SECTION 5. - DEFAULT

      5.1. Events of Default. The occurrence of any one or more of the following
events shall constitute an Event of Default hereunder:

            (a) Default in the payment of any of the Obligations, or in the
performance of any covenant or agreement contained or referred to herein;

                                     - 12 -
<PAGE>

            (b) Any warranty, representation or financial statement made or
furnished to the Secured Party by or on behalf of the Debtor proves to have been
false in any material respect when made or furnished;

            (c) The dissolution, termination of existence, or insolvency of the
Debtor, the application by the Debtor for the appointment of a receiver or
custodian for the Debtor or the Debtor's property, any assignment for the
benefit of creditors by the Debtor or the commencement of a voluntary case under
any bankruptcy or insolvency law by the Debtor or any guarantor or surety for
the Debtor.

            (d) The failure of the Debtor or any guarantor or surety for Debtor
within 60 days after the commencement of any involuntary case against it under
any bankruptcy or insolvency law to have such proceedings dismissed or stayed.

      5.2. Remedies. (a) Upon any such Event of Default and at any time
thereafter, the Secured Party may declare all of the Obligations immediately due
and payable without notice, protest, presentment or demand, all of which are
hereby expressly waived by the Debtor, and may proceed to enforce payment of the
same and exercise any and all of the rights and remedies provided by the Uniform
Commercial Code as well as all other rights and remedies possessed the Secured
Party. The Secured Party will give the Debtor reasonable notice of the time and
place of any public sale of the Collateral or any part thereof or of the time
after which any private sale or any other intended disposition thereof is to be
made. The requirements of reasonable notice shall be met if such notice is
mailed, postage prepaid, to the debtor at 1500 Avon Street Extended,
Charlottesville, Virginia 22901 at least five (5) days before the time of the
sale or disposition, but nothing contained herein shall be construed to mean
that any other notice of a shorter period of time does not constitute reasonable
notice for the sale of the Collateral, or any part thereof. Expenses of
retaking, holding, preparing for sale, selling or the like shall include the
Secured Party's reasonable attorney's fees and legal expenses. In such event of
default, the Debtor shall upon request by the Secured Party assemble the
Collateral or any designated part thereof and make it available to the Secured
Party at such place as is designated by the Secured Party.

            (b) License to Use Intellectual Property. If an Event of Default
shall have occurred and be continuing and for the purpose of enabling the
Secured Party to exercise its rights and remedies under this Agreement at such
time as the Secured Party shall be entitled to exercise such rights and
remedies, the Debtor hereby grants to the Secured Party an irrevocable,
nonexclusive license (exercisable without payment of royalty or other
compensation to the Debtor), to use, assign, license or sublicense any of the
Debtor's Intellectual Property, now owned or hereafter acquired by the Debtors
and wherever the same may be located, including in such license reasonable
access to all media in which any of the licensed items may be recorded or
stored; provided, however, that the Secured Party shall comply with all
pre-existing quality control standards and trademark use requirements of the
Debtor. The proceeds from, or other realization upon, any such license shall
constitute Collateral. No agreements hereafter acquired or agreed to or entered
into by the Debtor shall prohibit, restrict or impair the rights granted under
this Section.

                                     - 13 -
<PAGE>

            (c) The security interests, rights and remedies granted by the
Debtor to the Secured Party herein are in addition to any other rights,
collateral or other remedies which the Debtor or any other person has granted or
may hereafter grant to the Secured Party by any other instrument or through the
delivery of any document, instrument, chattel paper, or other collateral.

SECTION 6. - MISCELLANEOUS

      6.1. Headings. The titles and section headings herein are included for
convenience only and shall not be deemed to be a part of this Agreement.

      6.2. Nature of Rights. Each and every right granted to the Secured Party
hereunder or under any other document delivered hereunder or in connection
herewith or allowed it by law or equity shall be cumulative and may be exercised
from time to time. No failure on the part of the Secured Party to exercise, and
no delay in exercising, any right shall operate as a waiver thereof, nor shall
any single or partial exercise by the Secured Party of any right preclude any
other or future exercise thereof or the exercise of any other right. The terms
of this Agreement shall be binding upon the successors and assigns of the
parties hereto.

      6.3. Construction. This Agreement shall be governed and construed in
accordance with the internal substantive laws of the Commonwealth of Virginia
without giving effect to the conflict of law rules thereof. Wherever possible
each provision of this Agreement shall be interpreted in such manner as to be
effective and valid under applicable law, but if any provision of this Agreement
shall be prohibited by or invalid under such law, such provision shall be
ineffective to the extent of such prohibition or invalidity, without
invalidating the remainder of such provision or the remaining provisions of this
Agreement.

      IN WITNESS WHEREOF, the parties have executed this Agreement.

DEBTOR:                                BIOTAGE, INC.

                                       By: /s/ Mark Kachur
                                          ---------------------------
                                       Title:Pres/CEO
                                             ------------------------

SECURED PARTY:                         /s/ Sheridan G. Snyder
                                       ------------------------------
                                       Sheridan G. Snyder

                                     - 14 -
<PAGE>

                                    EXHIBIT A

                                     CONSENT

      The undersigned MILLIPORE CORPORATION, a Massachusetts corporation, as
licenser (the "Licensor") has previously entered into a certain License
Agreement, dated March 30, 1990 (the "License Agreement") with BIOTAGE,
INCORPORATED, a Delaware corporation, as licensee ("Licensee").

      Pursuant to the provisions of a certain security agreement, dated May 11,
1993 (the "Security Agreement") between the Licensee and Sheridan G. Snyder
("Snyder") the Licensee proposes to grant a security interest in and to, among
other things, all of Licensee's right, title and interest in and to the License
Agreement to secure repayment of the obligations of the Licensee to Snyder under
the terms and provisions of a line of credit to the Licensee in the principal
sum of up to $500,000 plus interest (the "Credit Line Note").

      Pursuant to the provisions of a certain assignment agreement, dated May
11, 1993 (the "Assignment Agreement"), between Snyder and Crestar Bank, N.A.
(the "Bank"), Snyder proposes to pledge, assign and grant to the Bank a security
interest in all rights, remedies, claims, interests and benefits now or
hereafter existing or arising in favor of the Bank under (i) the Credit Line
Note; and (ii) all proceeds receivable by Snyder from, and all security for all
of the foregoing including, but not limited to all collateral given to Snyder
pursuant to the Security Agreement.

      FOR VALUE RECEIVED, the Licensor hereby agrees as follows:

      1. The Licenser hereby consents to the transfer of the rights in and to
the License Agreement as set forth in the Security Agreement and the Assignment
Agreement, respectively, and further consents to the exercise by Snyder, or by
the Bank as his assignee (either individually or collectively the "Secured
party"), of the rights of the Secured Party under the Security Agreement or
Assignment Agreement as the case may be, as such rights may accrue and become
enforceable from time to time.

      2. Licenser agrees that if Licensee shall be in default under she License
Agreement, Licenser agrees that any Secured Party shall have the right, but not
the obligation, to remedy or cause so be remedied such default, whether the same
consists of the failure to pay any monetary amount or failure to do or perform
any other matter or thing which Licensee is required to do or perform, and
Licensor shall accept such performance on the part of the Secured Party as
though the same had been done or performed by Licensee. If an event of default
shall occur under the License Agreement, written notice shall be sent by
Licensor to Snyder and the Bank at the following addresses:

                                     - 15 -
<PAGE>

If to Snyder:

      Sheridan G. Snyder
      Route 1, Box 117
      Afton, Virginia 22920

If to the Bank:

      Crestar Bank
      Post Office Box 8088
      Charlottesville, Virginia 22906

Licensor agrees to take no action to terminate the License Agreement until
Licensor has given the Secured Party the following opportunities:

            A. If such default shall be in the payment of any monetary amount
payable under the License Agreement, the Secured Party shall be allowed a period
of thirty (30) days after the receipt of such notice within which to remedy such
default;

            B. If such default shall be in observing or performing any other
covenant or condition to be observed or performed by the Licensee under the
License Agreement, and such default can be remedied by the Secured Party, the
Secured Party shall be given the opportunity to remedy such default within such
period as may be necessary to remedy such default with diligence and continuity;
and

            C. If a Secured Party or a person designated by a Secured Party
shall become the owner of the interest of the Licensee upon the exercise of any
remedy provided for in the Security Agreement or the Assignment Agreement, such
Secured Party or other person shall have the right to assign to any person such
interest, but only upon the written consent of the Licenser, which consent shall
not be unreasonably withheld.

      3. If the License Agreement shall terminate for any reason, the Licenser
shall give the Secured Party written notice of such termination. The Secured
Party shall thereupon have the right exercisable by notice to Licenser within
sixty (60) days after the date of such notice of termination, to enter into a
new license for the subject matter of the License Agreement. The tern of such
new license shall begin on the date of termination of the License Agreement and
shall continue for the remainder of the original term of the License Agreement,
and such new agreement shall contain the same terms and conditions; provided,
however, that the Secured Party shall have remedied any default by the Licensee
under the terms of the License Agreement, as a condition to the obligation of
the Licensor to enter into such new agreement.

      4. The Licensor represents and warrants to the Secured Party that the
License Agreement is in full force and effect and has not been amended or
modified and that there are no existing defaults thereunder.

                                     - 16 -
<PAGE>

      IN WITNESS WHEREOF, the undersigned has caused this Consent to be executed
by its duly-authorized representative as of the date set forth below.

                                       MILLIPORE CORPORATION

Date:                                  By:
     ------------------------             ---------------------------
                                       Its:
                                           --------------------------

                                     - 17 -
<PAGE>

      THIS ASSIGNMENT AGREEMENT is made as of May 11, 1993, by SHERIDAN G.
SNYDER, a resident of Charlottesville, Virginia (the "Assignor"), to CRESTAR
BANK, N.A. (the "Bank").

      Pursuant to a Credit Line Note of even date made by Biotage, Inc. a
Delaware Corporation (the "Borrower") payable to the order of the Assignor in
the principal sum of up to $500,000.00 (the "Company Note"), Assignor agreed to
extend a line of credit to the Borrower in a principal amount up to $500,000.00.
Pursuant to a Commercial Note of even date made by the Assignor payable to the
order of the Bank in the principal sum of up to $500,000.00 (the "Assignor's
Note"), the Bank has agreed to make loans to Assignor in order to fund the
Company Note.

      As security for the payment of all of Assignor's obligations under the
Commercial Note, the Assignor intends to assign to the Bank (i) the Company
Note; and (ii) all proceeds receivable by Assignor from, and all security and
collateral for, all of the foregoing.

      NOW, THEREFORE, in order to induce the Bank to make loans to Assignor, the
parties agree as follows:

      (1) Assignment. Assignor hereby pledges and assigns to, and grants a
security interest to the Bank in, all rights, remedies, claims, interests and
benefits now or hereafter existing or arising in favor of the Assignor under (i)
the Company Note; and (ii) all proceeds receivable by the Assignor from, and all
security for all of the foregoing including, but not limited to all collateral
given to Assignor pursuant to a Security Agreement of even date between the
Borrower and the Assignor. The assignment made hereby shall include any and all
modifications, extensions and renewals of the obligations of Borrower under the
above described instruments.

      (2) Debt Secured. This Assignment is given for the purpose of securing:

            (a) Payment of the indebtedness evidenced by the Assignor's Note,
      including any renewals or extensions thereof.

            (b) Payment of all other sums with interest thereon becoming due and
      payable to the Bank under the provisions hereof.

            (c) Performance and discharge of all obligations, covenants and
      agreements of the Assignor herein and in the Assignor's Note.

      (3) Nature of Assignment. The assignment made hereby is executed as
collateral security, and the execution and delivery hereof shall not in any way
impair or diminish any obligations of the Assignor to the Bank under the
Assignor's Note or any obligations of the Assignor or of the Borrower to the
Assignor under the Company Note or the security Agreement, nor shall any of such
obligations be imposed upon the Bank. The Bank shall not be required to make any
inquiry as to the nature or sufficiency of any payment received by the Bank, or
to present or file any claim, or to take any other action to collect or enforce
the payment of any amounts which may have been assigned to the Bank or to which
it may be

                                     - 18 -
<PAGE>

entitled hereunder at any time. Assignor shall indemnify and hold harmless the
Bank from any liability, loss, damage or expense the Bank may incur under the
Company Note or Security Agreement by reason of this assignment. Upon the
payment of the principal of, and all interest on the Assignor's Note and the
performance and observance of the provisions thereof, the assignment made hereby
and all rights herein assigned to the Bank shall cease and terminate and all the
right, title and interest of the Bank in and to the above described assigned
property shall revert to the Assignor or to such person or persons as may be
legally entitled thereto, and the Bank shall at the request of the Assignor or
any such person, deliver to the Assignor an instrument, in recordable form,
canceling and discharging this Assignment.

      (4) Consent and Covenants of Borrower. At the request of the Assignor,
Borrower consents to the provisions of this Agreement and agrees during the term
of this Agreement: (i) to deliver directly to the Bank, at the address provided
for herein duplicate copies of all notices and other instruments or
communications required or permitted to be given or made by the Borrower
pursuant to the Company Note or Security Agreement; and (ii) to render
performance to the Bank of all its obligations under the Company Note or
Security Agreement which are required under the terms thereof to be rendered to
the Assignor. Borrower further agrees that it will not assert any offset,
counterclaim, reduction or defense in any proceeding brought under this
Assignment or otherwise. The Bank agrees with the Assignor and Borrower to apply
all remittances so received as provided in, or in accordance with instructions
received pursuant to, the Company Note or the Security Agreement.

      (5) Assignor's Covenants. (a) The Assignor agrees that the Assignment made
hereby and the designation and direction to Borrower hereinabove set forth and
consented to by Borrower are irrevocable and that the Assignor will not, while
this Assignment is in effect or thereafter until the Assignor has received from
the Bank notice of the termination of this Assignment, take any action which is
inconsistent with this Assignment, or make or suffer to be made any other
assignment, designation or direction of the subject matter hereof, and that any
such assignment, designation or direction shall be void. The Assignor will from
time to time, upon request of the Bank, execute all instruments of further
assurance as the Bank may reasonably specify.

            (b) The Assignor agrees not to cancel, modify, extend or in any way
alter the terms of the Security Agreement or the Company Note, not to anticipate
the payments thereunder except as provided therein, or to waive, excuse, condone
or in any manner release or discharge Borrower from the obligations, covenants,
conditions and agreements by Borrower to be performed, including the obligation
to make the payments called for thereunder in the manner and at the place and
time specified therein; and the Assignor does by these presents expressly
release, relinquish and surrender unto the Bank all the Assignor's right, power
and authority to cancel, amend, modify or in any way alter the terms or
provisions of the Security Agreement and the Company Note.

      (6) Representations and Warranties of Assignor. The Assignor represents
and warrants that the Security Agreement and the Company Note are in effect and
are not in

                                     - 19 -
<PAGE>

default; and the Assignor further represents and warrants that it has not
executed any other assignment of, or in any way affected, the subject matter of
this Agreement.

      (7) Rights Upon Default. Upon or at any time after default in the payment
of any obligation, covenant or agreement herein or under the Assignor's Note,
the Bank may declare all sums payable hereunder or under the Assignor's Note
immediately due and payable. The Bank may exercise any other rights available at
law or in equity, may fix or modify payments under the Company Note and may
issue in its own name and collect amounts due under the Company Note, including
reasonable attorney's fees as provided therein.

      (8) Appointment of Attorney-in-Fact. The Assignor hereby irrevocably
constitutes and appoints the Bank, or any officer of the Bank whom the Bank
shall designate, as his true and lawful attorney-in-fact, during the entire term
of this Agreement, with full power of substitution, for him and in his name to
demand, require, receive, collect, compound and give discharges and releases of
all claims for any and all proceeds of the Company Note and all other moneys due
or to become due under the Security Agreement and to endorse any checks and
other instruments or orders in connection therewith, and, if any event of
default specified in the Assignor's Note shall occur; (a) to settle, compromise,
compound or adjust any such claims; (b) to exercise and enforce any and all
claims, rights or remedies of every kind and description of the Assignor arising
out of the Company Note and Security Agreement; (c) to file, commence and
prosecute any suits, actions or proceedings at law or in equity in any court of
competent jurisdiction, to collect any such sums assigned by the Assignor
hereunder or to enforce any rights with respect thereto and all other claims,
rights and remedies of every kind and description of the Assignor arising out of
the Company Note and Security Agreement; and (d) generally to sell, assign,
transfer, pledge, make any agreement with respect to or otherwise deal with any
of such claims, rights and remedies as fully and completely as though the Bank
were the absolute owner thereof for all purposes, and at such times and in such
manner as may seem to the Bank to be necessary or advisable in its absolute
discretion.

      (9)  Successors and Assigns. This Assignment shall be binding upon, inure
to the benefit of and be enforceable by the parties hereto and their respective
successors and assigns.

      (10) Notices. All notices, demands, approvals, consents, requests and
other communications hereunder shall be in writing and, unless otherwise
provided herein, shall be deemed to have been given when delivered in person or
mailed by first class registered or certified mail, postage prepaid, addressed
as follows:

                   (i)  if to the Assignor, to

                        Sheridan G. Snyder
                        2611 West Main Street, Suite 1
                        Waynesboro, VA  22980

                                     - 20 -
<PAGE>

                  (ii)  if to the Bank at
                        High and Park Streets
                        P.O. Box 8088
                        Charlottesville, Virginia  22906
                        Attn: Ms. Linda W. Hitchings
                              Vice President

                 (iii)  if to Borrower, to

                        Biotage, Inc.
                        1500 Avon Street Extended
                        Charlottesville, VA  22901

      The Assignor, the Bank and Borrower may, by notice given hereunder,
designate any further or different addresses to which subsequent notices,
demands, approvals, consents, requests or other communications shall be sent by
person to whose attention the same shall be directed.

      (11) Severability. If any clause, provision or section of this Assignment
be held illegal or invalid by any court, the illegality or invalidity of such
clause, provision or section shall not affect any of the remaining clauses,
provisions or sections hereof, and this Assignment shall be construed and
enforced as if such illegal or invalid clause, provision or section had not been
contained herein. In case any agreement or obligation contained in this
Assignment be held to be in violation of law, then such agreement or obligation
of the parties hereto to the full extent permitted by law.

      (12) Headings. The headings of the several sections of this Assignment are
inserted for convenience only, and do not comprise a part hereof.

      (13) Applicable Law. This Assignment shall be governed by the applicable
laws of the Commonwealth of Virginia.

      (14) Execution by Borrower. The Borrower has signed this Agreement for the
sole purpose of being bound by the consents and covenants set forth in paragraph
4 of this Agreement.

      IN WITNESS WHEREOF, the parties have cause this Assignment to be executed
as of the date first above written.

ASSIGNOR:                              /s/ Sheridan G. Snyder
                                       ------------------------------
                                       SHERIDAN G. SNYDER

THE BANK:                              CRESTAR BANK

                                       By: /s/ Linda W. Hitchings
                                          ---------------------------
                                          Its: Vice President
                                              -----------------------

THE BORROWER:                          BIOTAGE, INC. a Delaware
                                       Corporation

                                       By: /s/ Mark Kachur
                                          ---------------------------
                                          Its: Pres/CEO
                                              -----------------------

                                     - 21 -
<PAGE>

THE BORROWER:                              BIOTAGE, INC., a Delaware corporation

                                       By: /s/ Mark Kachur
                                          ---------------------------
                                          Its: Pres/CEO
                                              -----------------------

                                     - 22 -
<PAGE>

                         AMENDMENT TO SECURITY AGREEMENT
                           AND TO ASSIGNMENT AGREEMENT

      This Amendment to Security Agreement and to Assignment Agreement (this
"Amendment") is made as of August 10, 1995 among Biotage, Inc., a Delaware
corporation (the "Borrower"), Sheridan G. Snyder (the "Assignor") and Crestar
Bank, N.A. (the "Bank").

                                   Recitals

      A. The Assignor has extended a line of credit to the Borrower evidenced by
a Credit Line Note dated as of May 11, 1993 in the principal amount of
$500,000.00 (the "Company Note") secured by a security agreement (the "Security
Agreement") of even date therewith pledging substantially all of the personal
property of the Borrower, including without limitation all after acquired
intellectual property.

      B. The Assignor has assigned all of his rights, remedies, claims and
interests under the Company Note and the Security Agreement to the Bank pursuant
to an assignment agreement (the "Assignment") dated as of May 11, 1993 between
the Assignor and the Bank.

      C. In order to permit the Borrower to raise over $1.5 million of
additional equity financing and to acquire certain technology through the
acquisition of Protein Engineering Corporation ("PEC"), and subject to the terms
and conditions of this Amendment, the Assignor and the Bank are prepared to
amend the Security Agreement and the Assignment to substitute the Company Note
with a new term note of the Borrower and to release certain collateral that
would otherwise be subject to the lien of the Security Agreement pursuant to the
after-acquired property provisions thereof.

      NOW, THEREFORE, the parties agree as follows:

      (1) The Company Note will be surrendered immediately by the Bank, on
behalf of the Bank and the Assignor, to the Borrower in exchange for a new
secured convertible term note of the Borrower in substantially the form of
Exhibit A hereto (the "New Note"). The New Note will be held by the Bank and all
references in the Assignment and the Security Agreement to the "Company Note" or
the "Credit Line Note", as the case may be, will hereafter be deemed to be
references to the New Note.

      (2) The term "Intellectual Property" as defined in the Security Agreement
is hereby amended to exclude therefrom, and thereby to release from the lien of
the Security Agreement thereon, any patents and other technology and
intellectual property licensed or otherwise acquired from PEC or its subsidiary,
P.E.C. Technology Corp., by the Borrower, whether now existing or hereafter
acquired, and all proceeds of the foregoing exclusions.

      (3) The Assignor and the Bank agree to execute and deliver to the Borrower
any UCC financing statements that the Borrower may reasonably request to further
evidence and confirm the release of collateral from the lien of the Security
Agreement set forth in Section 2 above.

                                     - 23 -
<PAGE>

      (4) The parties hereto agree that, except as set forth above, in all other
respects the Security Agreement and the Assignment remain in full force and
effect.

      IN WITNESS WHEREOF, the parties have caused this Amendment to be executed
as of the date first above written.

BORROWER:                              BIOTAGE, INC.

                                       By: /s/ Robert Dishman
                                          ---------------------------
                                               Its:
                                                   ------------------

ASSIGNOR:

                                       /s/ Sheridan G. Snyder
                                       ------------------------------
                                       SHERIDAN G. SNYDER

BANK:                                  CRESTAR BANK, N.A.

                                       By: /s/ Linda W. Hitchings
                                          ---------------------------
                                                Its: Vice President
                                                    -----------------

                                     - 24 -

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