Document:

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                                                                Exhibit 10.13

                      LINE OF CREDIT AND GUARANTY AGREEMENT

                                                              January 25, 2000

Boston Safe Deposit & Trust Company
One Boston Place
Boston, Massachusetts  02108

Ladies and Gentlemen:

     Staples, Inc., with a mailing address at 500 Staples Drive, Framingham,
Massachusetts 01702 ("Customer") hereby agrees with your bank ("Bank") as
follows regarding a line of credit for term loans to be made by your Bank from
time to time to employees of Customer ("Loans"):

     1.   Line Of Credit. Subject to the terms and conditions hereof, Bank
shall make available a line of credit (the "Line of Credit") for term loans
of U.S. dollars to Eligible Employees (as defined herein) during the period
from the date hereof through January 31, 2000. The maximum principal amount
of Loans outstanding at any one time under the Line of Credit shall at no
time exceed $2,000,000.

     2.   Loans. (a) Each Loan shall be in a minimum amount of $30,000 and a
maximum amount of $700,000. Each Loan shall be evidenced by a promissory note
of the Eligible Employee obligated thereon in the form of Exhibit A hereto (a
"Note") and shall be secured by such Eligible Employee's Staples.com common
stock and, prior to the issuance of such stock, all of such Eligible
Employee's rights or options with respect to the same (the "Tracking Stock")
pursuant to the Eligible Employee's Pledge Agreement covering the Tracking
Stock delivered to Bank in connection with Bank's Demand Loan (as hereinafter
defined) to such Eligible Employee. As used herein, the term "Eligible
Employee" shall mean an employee of Customer designated by the Customer as
eligible to obtain Loans who: (i) is not a debtor in any pending case under
the federal Bankruptcy Code or any state insolvency or receivership law and
whose assets are not subject to any receivership, assignment or trust
mortgage for the benefit of creditors, (ii) has delivered to the bank a
short-form personal financial statement on a form supplied by the Bank, and
(iii) has a prior credit history acceptable to Bank in its sole discretion.
Each Loan shall be issued by the Bank subject to the terms and conditions of
this Agreement.

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     (b)  The proceeds of the Loans shall be used by Eligible Employees to
finance interest payments due with respect to demand loans made to Eligible
Employees by Bank ("Demand Loans"). The proceeds of the Loans shall be disbursed
by Bank as such interest payments come due, and the maximum amount advanced to
any Eligible Employee with respect to a Loan shall not exceed 20% of the
principal amount of the Demand Loan owed by such Eligible Employee to Bank.

     (c)  Upon sale of any Tracking Stock by an Eligible Employee, the proceeds
of such sale shall be applied: (i) first, to the repayment of amounts due to the
Bank with respect to such Eligible Employee's Demand Loan as provided in the
Line of Credit and Guaranty Agreement between Bank and Customer dated December
6, 1999, as amended, (ii) second, to the repayment of the outstanding principal
balance of and any accrued interest on such Eligible Employee's Loan, with any
proceeds in excess of such amount to be paid: (iii) so long as an Employee
Default by such Eligible Employee shall not have occurred and be continuing, to
the Eligible Employee obligated on such Loan, or (iv) if an Employee Default by
such Eligible Employee shall have occurred and be continuing and (A) the
Customer shall have purchased the Note of such Eligible Employee pursuant to
Section 4(c), to the Customer, and (B) if the Customer shall not have purchased
the Note of such Eligible Employee pursuant to Section 4(c), to all other
obligations of such Eligible Employee to the Bank in such order as Bank may
determine in its sole discretion.

     3.   Interest. (a) As used herein, the following terms shall have the
following meanings:

     i.   "Call Rate" shall mean the rate quoted from time to time in the "Money
          Rates" section of The Wall Street Journal as "Call Money," or if no
          such rate is quoted or The Wall Street Journal is not available, the
          generally prevailing rate for loans to members of the New York Stock
          Exchange secured by stock exchange collateral provided by Reuters or a
          similar source of recognized standing selected by the Bank. In the
          event Bank determines that for any reason no rate comparable to Call
          Money is available on a given day, the Loans shall bear interest on
          such date at the Prime Rate (as hereinafter defined) minus 1% per
          annum unless a penalty rate is applicable to such Loan pursuant to the
          Note evidencing the same.

     ii.  "Standard Notice" shall mean an irrevocable notice provided to the
          Bank in writing (including by facsimile) or by telephone confirmed in
          writing on a Business Day which is at least one Business Day in
          advance in case of notification of request for a Loan. Standard Notice
          must be provided no

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later than 1:00 p.m., Eastern Standard Time on the last day permitted for such
notice.

     (b)  Interest on the Loans shall be payable monthly in arrears on the first
day of each month commencing on the first day of the month succeeding that in
which the proceeds of a Loan are first disbursed. Interest on the Loans shall be
calculated on the basis of the actual number of days elapsed and a year of 360
days. Each change in the Call Rate shall be reflected by a simultaneous change
in the rate of interest payable on the Loans. In the event any payment of
interest required to be made under a Note is not made within 15 calendar days of
the date when due, the Eligible Employee obligated thereon shall pay a late
charge to the Bank of 5% of the amount due or $25, whichever is greater. Such
charge must be paid within 30 days of the date it is assessed and will be
charged only once on each late payment. If any payment due under the Guaranty is
not made on or within five Business Days of the date when due, such amount shall
thereafter bear interest payable on demand at a fluctuating rate per annum equal
to the greater of: (a) two percent (2%) above the Call Rate (or one percent (1%)
above the Prime Rate, if the Call Rate is unavailable) in effect on such due
date, or (b) two percent (2%) above the Call Rate (or one percent (1%) above the
Prime Rate, if the Call Rate is unavailable) in effect from time to time
thereafter. As used in this Agreement, "Prime Rate" shall mean the rate quoted
as the "Prime Rate" in the "Money Rates" section of The Wall Street Journal. In
the event the Call Rate or the Prime Rate is reported as a range of rates, the
rate used to calculate the interest rates under this Agreement shall be the
highest such rate reported. Each change in the Call Rate or the Prime Rate shall
be reflected in a corresponding change in the fluctuating rate payable pursuant
to this subsection 3(b).

     (c)  If due to either (i) the introduction of or any change in or in the
interpretation of any law or regulation or (ii) the compliance with any
guideline or request from any central bank or other governmental authority
(whether or not having the force of law), in each case after the date of this
Agreement, there shall be any increase in the cost to the Bank of agreeing to
make or making, funding or maintaining any Loan (excluding for purposes of this
subsection 3(c) any such increased costs resulting from changes in the basis of
taxation of overall net income or overall gross income of the Bank by the United
States or any political subdivision thereof), then the Eligible Employee
obligated on a Note shall, from time to time, within 5 Business Days after
demand by the Bank, pay to the Bank additional amounts sufficient to compensate
the Bank for such increased costs.

     (d)  If the Bank determines that compliance with any law or regulation or
any guideline or request from any central bank or other governmental authority
(whether or not having the force of law) introduced or changed after the date of
this Agreement affects the amount of capital required to be maintained by the
Bank and that the amount of such capital is increased by or based upon the
existence of the Bank's

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commitment to lend hereunder, then, within 5 Business Days after demand by the
Bank, each Eligible Employee shall pay to the Bank additional amounts sufficient
to compensate the Bank in the light of such circumstances.

     (e)  Bank shall notify Eligible Employees and the Customer promptly after
the occurrence of any event described in subsections (c) and (d) above, and
Customer's liability to Bank pursuant to such subsections shall be limited to
amounts accruing after the date of such notice. Demand by the Bank pursuant to
subsections 3(c) or (d) shall be accompanied by a certificate as to the amount
of such increased cost or required capital, respectively, showing calculations
of the amount claimed in reasonable detail. Bank's determination of any such
increased cost (using any reasonable method of averaging, attribution or
allocation), as set forth in such a certificate shall, if correctly calculated,
be deemed PRIMA FACIE evidence of such amount.

     4.   Guaranty. (a) The Customer hereby unconditionally guarantees full and
punctual payment, performance and fulfillment to the Bank of all liabilities,
obligations and undertakings of Eligible Employees to the Bank pursuant to the
Loans, whether direct or indirect, absolute or contingent, due or to become due,
now existing or hereafter arising or acquired (the "Obligations") on January 31,
2002 or earlier upon the occurrence of an Employee Default or a Customer Default
as provided herein or under the circumstances described in subsection 9(b).

     (b)  The Customer's agreement contained in this Section 4 ("the Guaranty")
shall operate as a continuing, absolute and unconditional guaranty of the full
and punctual payment and performance of the Obligations, and not of their
collectibility only, and the Bank shall be entitled to enforce the Guaranty
against all assets of the Customer for the full amount of the Obligations. If an
Employee Default shall occur, the liability of the Customer with respect to the
Obligations of the defaulting Eligible Employee shall become immediately due and
payable, and if a Customer Default shall occur, the liability of the Customer
with respect to all Obligations of all Eligible Employees shall become
immediately due and payable to the Bank upon written notice to Customer. The
Customer waives any right that the Customer may have to require the Bank first
to proceed against an Eligible Employee or any other person. The Customer also
waives any right that the Customer may have to require the Bank to realize on
any security held by the Bank before proceeding against the Customer for the
enforcement of the Guaranty.

     (c)  Bank agrees to consider joint requests by Customer and particular
Eligible Employees to sell such Eligible Employees' Tracking Stock prior to
enforcing its rights under the Guaranty with respect to such Tracking Stock, but
shall be under no obligation to do so. Bank agrees that, prior to making demand
upon an Eligible Employee for payment of a Loan following an Employee Default,
it will provide Customer with notice of such Employee Default and, except when
stayed from

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enforcing the Guaranty against the Customer as a result of proceedings under the
federal Bankruptcy Code or any state insolvency or receivership law or by court
order, or under circumstances in which the prospects for obtaining repayment of
such Loan from the defaulting Eligible Employee would be impaired by delay, to
permit Customer to promptly purchase the Note of such Eligible Employee at a
purchase price equal to the outstanding principal balance thereof, accrued
interest and late fees thereon, and costs of collection with respect thereto,
prior to making demand upon such Eligible Employee, without waiving its right to
proceed first against such Eligible Employee for the enforcement of such Note.

     (d)  Upon purchase by the Customer of the Note of any Eligible Employee,
the Bank shall endorse and transfer to the Customer the Note of such Eligible
Employee and (unless the Tracking Stock of such Eligible Employee has been sold
by Bank) shall deliver to the Customer the Pledge Agreement of such Eligible
Employee and the Tracking Stock of such Eligible Employee, in each case without
recourse, warranty or representation. The Customer waives any other right that
it may have against the Bank as a result of any such payment by the Customer
under the Guaranty, whether arising by way of subrogation, contribution,
reimbursement or otherwise.

     (e)  The liability of the Customer under the Guaranty shall be unlimited.
The Customer agrees, as a principal and not as a surety only, to pay to the
Bank, on demand, all costs and expenses paid or incurred by the Bank (including
court costs and attorneys' fees) in connection with the Obligations or the
Guaranty and the enforcement of either of them, including without limitation
costs and expenses paid or incurred by the Bank in connection with any
proceedings under the federal Bankruptcy Code or any other law relating to
insolvency.

     (f)  The Customer waives presentment, demand, protest, notice of
acceptance, notice of the Obligations incurred and all other notices of any kind
and all defenses which may be available to the Customer except for notices
expressly provided for herein. The Customer warrants to the Bank that it has
adequate means to obtain from Eligible Employees, on a continuing basis,
information concerning the financial condition of the Eligible Employees, and
that it is not relying on the Bank to provide such information, now or in the
future. The Customer agrees to the provisions of any instrument, security or
other writing evidencing or securing any of the Obligations and agrees that the
obligations of the Customer hereunder shall not be released or discharged, in
whole or in part, by: (i) any renewals, extensions or postponements of the time
of payment of any of the Obligations or any other forbearance or indulgence with
respect thereto; (ii) any rescissions, waivers, amendments or modifications of
any of the terms of any agreement evidencing, securing or otherwise executed in
connection with the Obligations; or (iii) the substitution or release of any
security for the Obligations or of any other person primarily or secondarily
liable on any of the Obligations, whether or not notice thereof shall be given
to the Customer. The

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enforcement of the Guaranty shall not be affected by the delay, neglect or
failure of the Bank to take any action with respect to any security, right,
obligation, endorsement, guaranty or other means of collecting the Obligations
which it may at any time hold, including perfection or enforcement thereof. The
Customer agrees that the Customer shall be and remain bound upon the Guaranty
irrespective of any action, delay or omission by the Bank in dealing with any
Eligible Employee, any of the Obligations, any Tracking Stock or other
collateral therefor, or any person at any time liable with respect to the
Obligations, and irrespective of any defense which any Eligible Employee may
assert to the underlying debt, including but not limited to failure of
consideration, breach of warranty, fraud, payment, statute of frauds,
bankruptcy, lack of legal capacity, statute of limitations, lender liability,
accord and satisfaction or usury.

     (g)  If for any reason an Eligible Employee is under no legal obligation to
discharge any of the Obligations, or if any of the Obligations shall have become
irrecoverable from an Eligible Employee by operation of law or for any other
reason, or if any security for or other guaranty of the Obligations shall be
found invalid, the Customer shall nonetheless be and remain bound on the
Guaranty. The Guaranty shall continue to be effective or be reinstated,
notwithstanding any prior termination, if at any time any payment made or value
received with respect to any of the Obligations is rescinded or must otherwise
be returned by the Bank due to the insolvency or bankruptcy of an Eligible
Employee or otherwise, all as though such payment had not been made or value
received.

     5.   Representations, Warranties And Covenants.

     (a)  To induce Bank to make the Loans, the Customer makes the following
representations and warranties:

     (i)  That the Customer is a duly organized and validly existing corporation
in good standing under the laws of the State of Delaware, with corporate powers
adequate for the making and performing of this Agreement, for the issuance of
the Guaranty and the other agreements of the Customer referred to herein, and
for the carrying on of the business now conducted by it. The Customer is duly
qualified as a foreign corporation to do business wherever necessary to carry on
its present operations and is in good standing in every jurisdiction where such
qualification is necessary.

     (ii) That Customer has good and marketable title in fee to such of its
fixed assets as are real property and good and marketable title to its other
properties and assets, subject to no mortgage, pledge, lien, charge, security
interest, title retention agreement or other encumbrance except for encumbrances
permitted by the Senior Credit Agreement (as hereinafter defined), and that the
obligations of the Customer pursuant to the Senior Credit Agreement are
unsecured except for rights of setoff of the Banks referred to therein.

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     (iii) That the financial statements of the Customer contained in the
Customer's Annual Report on Form 10-K for the fiscal year ended January 31,
1999, and the Customer's Quarterly Report on Form 10-Q for the quarter ended
October 31, 1999, in each case filed with the Securities and Exchange
Commission, are complete and correct and present fairly the financial position
of the Customer as of the dates thereof and for the periods included therein,
and have been prepared in accordance with generally accepted accounting
principles consistently applied throughout the periods involved, subject, as to
interim statements, to audit and year-end adjustments. There are no material
contingent liabilities or liabilities for taxes of the Customer as at the date
of the aforementioned Quarterly Report on Form 10-Q which are not reflected in
said statements of financial condition.

     (iv) That there has been no material adverse change in the condition,
financial or otherwise, of the Customer since the date as of the aforementioned
Quarterly Report on Form 10-Q other than normal seasonal variations occurring in
the ordinary course of business.

     (v)  That the Customer has filed or caused to be filed all federal, state
and local tax returns which are required to be filed, and has paid or caused to
be paid all taxes as shown on said returns or any assessment received by it, to
the extent that such taxes have become due, except as otherwise permitted by the
provisions of this Agreement.

     (vi) That there are no actions, suits or proceedings pending or, to the
knowledge of the Customer, threatened against the Customer at law or in equity
or before or by any federal, state, municipal or other governmental department,
commission, board, bureau, agency or instrumentality, which in the reasonable
opinion of Customer is likely to result in a material adverse change to the
business, properties or assets or in the condition, financial or otherwise, of
the Customer.

     (vii) That the Customer is not a party to any contract or agreement or
subject to any restrictions which materially and adversely affects its business
or assets or financial condition. Neither the execution nor delivery nor
compliance with the terms and provisions of this Agreement or the Guaranty will
be contrary to the provisions of, or constitute a default under, the charter or
by-laws of the Customer or any agreement to which the Customer is a party.

     (viii) That the making and performance of this Agreement and the Guaranty
are within the Customer's corporate powers and have been duly authorized by all
necessary corporate action, and that this Agreement and the Guaranty are legal
and binding obligations of the Customer enforceable in accordance with their
respective

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terms (subject to bankruptcy and similar laws of general application affecting
the rights and remedies of creditors).

     (ix) That no approval or authorization of, or registration, qualification
or filing with, any governmental authority is required in connection with the
execution, delivery or performance by the Customer of this Agreement or the
Guaranty or the consummation of the transactions contemplated hereby or thereby.

     (x)  That the Customer possesses all patents, patent rights or licenses,
trademarks, trademark rights, trade names, trade name rights and copyrights
which are required to conduct its businesses as now conducted without known
conflict with the rights of others.

     (xi) That Company is not engaged principally, or as one of its important
activities, in the business of extending credit for the purpose of purchasing or
carrying margin stock (within the meaning of Regulation U of the Board of
Governors of the Federal Reserve System), and no part of the proceeds of any
extension of credit under this Agreement will be used to purchase or carry any
such margin stock or to extend credit to others for the purpose of purchasing or
carrying any such margin stock.

     (xii) That the most recent annual report filed by the Customer pursuant to
Section 104 of the Employee Retirement Income Security Act of 1974, as amended
("ERISA"), including without limitation, all related financial and actuarial
statements, is complete and correct, and no event has occurred and is continuing
which would permit the Pension Benefit Guaranty Corporation ("PBGC") established
under ERISA to institute proceedings to terminate any pension plan or other type
of employee benefit which the PBGC has elected to insure, established or
maintained by the Customer.

     (b)  The Customer hereby covenants and agrees with the Bank as follows:

     (i)  To comply with the covenants contained in the Revolving Credit
Agreement dated as of November 13, 1997 among the Customer, BankBoston, N.A. as
Administrative Agent, The Chase Manhattan Bank as Syndication Agent, Fleet
National Bank as Documentation Agent and the Co-Agents named therein, or any
agreement pursuant to which the loans contemplated thereby are refinanced or the
Commitments of the Banks (as those terms are defined therein) are replaced
(together, the "Senior Credit Agreement"), as the same may be amended from time
to time.

     (ii) At any time that Mellon Bank, N.A. shall cease to be a lender pursuant
to the Senior Credit Agreement, to provide to the Bank: (A) notice of the
amendment of any provision of the Senior Credit Agreement promptly after the
same is executed, (B) copies of the financial statements, certificates and
information referred to in Section 6.4 of the

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Senior Credit Agreement, at the time the same are provided to the Agent
thereunder, and (C) copies of the notices referred to in Section 6.5 of the
Senior Credit Agreement, at the time the same arE provided to the Agent
thereunder, or in the event that the Senior Credit Agreement in effect on the
date hereof is replaced, comparable notices, financial statements, certificates
and information required to be provided to the Agent under such replacement
Senior Credit Agreement.

     (iii) In the event that the Customer grants to the Agent under the Senior
Credit Agreement any collateral or rights in property of the Customer for the
benefit of the Banks referred to therein, the Customer shall grant to the Bank
an equal and ratable security interest or mortgage on such property to secure
the Customer's obligations under the Guaranty.

     (iv) That the Customer shall provide to the Bank quarterly, within 30 days
after the end of each fiscal quarter of the Customer, a list of Eligible
Employees including a statement as to any change in the status of any individual
previously identified to the Bank as an Eligible Employee.

     (v)  That the Tracking Stock is fully paid and non-assessable and is not
subject to any lien, security interest, right or claim on the part of Customer
except for: (A) the Customer's right to purchase non-vested Tracking Stock from
Eligible Employees and (B) a junior security interest therein to secure such
right. Bank acknowledges that it holds, and will cause its agents (including the
Fiduciary under any Pledge Agreement) to hold, each Eligible Employee's Tracking
Stock to perfect the Customer's junior security interest therein, and that, upon
prior payment in full of all Obligations (as defined in each Eligible Employee's
Pledge Agreement), it will deliver the Collateral described in such Pledge
Agreement to the Customer.

     (vi) The security interest of the Customer in the Collateral described in
the Pledge Agreement shall be fully subordinate and junior to Bank's security
interest in such assets, regardless of the time Bank's security interest with
regard to such assets attaches, and regardless of the future granting of loans
or credits to Eligible Employees by Bank. Customer agrees that it will do
nothing to interfere with Bank's prior security interest in such Collateral
whether by undertaking to collect or enforce its rights in such Collateral or
otherwise until all indebtedness of the Eligible Employee who owns the same to
the Bank shall be paid in full.

     6.   Conditions Precedent. (a) The Bank's agreement to extend the Line of
Credit is subject to the conditions that:

     i.   On or before the date hereof the Customer shall have delivered to the
     Bank the documents, instruments and certificates listed on Exhibit B hereto
     and

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     such other documents and materials as the Bank may reasonably require.

     ii.  On or before the date of each Loan, the Eligible Employee to be
     obligated thereon shall have executed and delivered to the Bank: (i) the
     Note evidencing such Loan, (ii) the Pledge Agreement securing such Note, or
     a confirmation of a Pledge Agreement previously executed by such Eligible
     Employee, and (iii) such other documents, instruments and materials as Bank
     may reasonably require.

     (b)  The Bank's agreement to make each disbursement of proceeds of a
Loan to an employee of the Customer is subject to the further conditions
precedent that: (i) no Customer Default shall have occurred and be
outstanding hereunder, (ii) the employee to be obligated thereon is at the
time an Eligible Employee, and (iii) no Employee Default with respect to such
employee shall have occurred and be outstanding as to the Demand Loan of such
employee or as to payments of interest due with respect to principal of such
employee's Loan previously disbursed.

     7.   Employee Defaults.

     (a)  The following shall constitute Employee Defaults with respect to a
Note:

     (i)  Default in the payment or performance of any Obligation by the
Eligible Employee obligated thereon, including the Loan and the Demand Loan of
such Eligible Employee.

     (ii) Death of the Eligible Employee obligated thereon.

     (iii) Such employee shall cease to be an employee of Customer or shall
cease to be an Eligible Employee.

     (iv) Customer shall notify Bank that the employee obligated thereon is no
longer eligible to participate in Customer's program of obtaining Loans for
Eligible Employees from the Bank.

     (v)  The employee obligated thereon shall become subject to any injunction
or temporary restraining order restricting the sale of the Tracking Stock or any
order prohibiting the Bank from selling such employee's Tracking Stock shall be
entered by any court, or such employee shall become the subject of any
investigative or administrative proceeding or any civil or criminal action
alleging violation of state or federal securities laws.

     (vi) The employee obligated thereon shall sell or transfer all or
substantially all of his or her assets, or become insolvent, or fail generally
to pay his or

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her debts as they become due, or if a receiver is appointed for such employee or
any part of the property of such employee or if such employee shall make an
assignment or grant a trust mortgage for the benefit of (or composition with)
the creditors of such employee, or if a material adverse change shall occur in
the financial condition of such employee.

     (vii) The filing of a petition in bankruptcy by or against the employee
obligated thereon or the commencement of any proceedings by or against such
employee under any insolvency or other laws relating to the relief of debtors;
or the taking of any action by such employee to accomplish any of the foregoing.

     (b)  Upon the occurrence of an Employee Default: (i) Bank's agreement to
make further advances under the Note of such Eligible Employee shall immediately
termination, and (ii) all of the Obligations of the defaulting employee shall
become immediately due and payable, and the liability of the Customer pursuant
to the Guaranty with respect to such Obligations shall (unless Bank otherwise
elects) become immediately due and payable without demand, presentment or
notice, notwithstanding any prior acceptance by Bank of periodic payments of
interest on such employee's Note or other Obligations.

     8.   Customer Defaults. (a) The following shall constitute Customer
Defaults:

          (i)  The Customer shall default in the payment or performance of any
obligation contained in the Senior Credit Agreement, as the same may be amended
from time to time, and such default shall continue beyond any applicable grace
period, whether or not such default is waived.

          (ii) The Customer shall default in the payment or performance of any
obligation contained in this Agreement, including default in the payment of any
sums due pursuant to the Guaranty continuing for five Business Days following
demand by Bank.

     (b)  Upon the occurrence of a Customer Default, all Obligations shall
become immediately due and payable, and the liability of the Customer pursuant
to the Guaranty shall (unless Bank otherwise elects) become immediately due and
payable without demand, presentment or notice.

     9.   Bank's Rights And Remedies. (a) Upon the occurrence of an Employee
Default, Bank shall have the rights and remedies of a secured party under the
UCC with respect to the Tracking Stock pledged by the defaulting employee of
Customer. Upon the occurrence of a Customer Default, Bank shall have the rights
and remedies of a secured party under the UCC with respect to all Tracking Stock
pledged as security for

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the Obligations. The Customer hereby agrees that five Business Days' notice of
the time and place of any public sale of Tracking Stock, or the time after which
a private sale or other disposition of Tracking Stock shall take place, sent by
telefacsimile to the Customer at 508/___-____, attention: Chief Financial
Officer, shall constitute reasonable notification.

     (b)  Upon the occurrence of an Employee Default or a Customer Default,
Bank may take control of any proceeds of Tracking Stock. Any deposits or other
sums at any time credited by or due from the Bank to the Customer shall at all
times constitute collateral for the Obligations and the Guaranty. Bank may apply
or set-off deposits against the Obligations and the Guaranty regardless of the
adequacy of any other collateral at any time after the occurrence and during the
continuance of a Customer Default. Upon the occurrence and during the
continuance of a Customer Default, Bank may apply the net proceeds of any sale
of Tracking Stock to the Obligations of the owner of such Tracking Stock and may
apply the proceeds of any set-off to the Customer's obligations under the
Guaranty, in each case in such order as it may determine.

     (b)  Bank shall have the option at any time within 90 days after the date
on which Mellon Bank, N.A. ceases to be a lender to the Customer pursuant to the
Senior Credit Agreement to require the Customer to refinance all outstanding
Loans or to repay all outstanding Loans pursuant to the Guaranty.

     (c)  In the event that: (i) the Commitments of the Banks under the Senior
Credit Agreement are reduced or (ii) the principal balance of the Loans
outstanding thereunder is repaid following an Event of Default thereunder, the
Customer shall upon demand by Bank deliver to Bank cash collateral (and a pledge
agreement covering the same) in an amount computed by multiplying: (A) the
amount of such reduction of Commitments or repayment of Loans, by a fraction,
(B) the numerator of which shall be $1,700,000 and (C) the denominator of which
shall be the maximum amount of the Commitments, or the principal balance of the
Loans outstanding under the Senior Credit Agreement, as the case may be, prior
to such reduction or repayment.

     10.  Customer's Agreement To Indemnify Bank. Customer agrees to indemnify
Bank and hold it harmless from any loss, cost (including legal costs and
reasonable attorneys' fees) or damage it may suffer as a result of: (i) any
failure of the Customer or an employee of Customer to comply with the terms of
this Agreement or a Note, (ii) obligations and responsibilities imposed by state
or federal securities laws, (iii) Bank's foreclosure upon any Tracking Stock to
satisfy an Employee Default or enforcement of any Note, or (iv) all other
claims, demands, suits, liabilities or obligations arising out of Bank's
agreement to make the Loans as provided herein.

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<PAGE>

     11.  Miscellaneous. (a) The Customer shall from time to time designate, and
shall at all times maintain, a management employee authorized to certify as to
the eligibility of employees to obtain Loans hereunder, and shall promptly
notify Bank in the event that an employee to whom a Loan is outstanding shall
cease to be so eligible.

     (b)  This Agreement and the Guaranty represent the entire understanding
between the Bank and the Customer with regard to the Loans, and their respective
provisions may not be modified, waived or amended except by a writing signed by
the Bank and the Customer. This Agreement is entered into solely for the benefit
of the Customer and the Bank, and no other party, including Eligible Employees
designated by the Customer from time to time, shall have any rights hereunder.
THE CUSTOMER WAIVES TRIAL BY JURY IN ANY ACTION ARISING OUT OF THIS AGREEMENT OR
THE GUARANTY.

     (c)  All notices provided for hereunder shall be in writing to the parties
at their respective addresses set forth on page one, or to such other address or
facsimile number as either party may designate in writing to the other. Notices
shall be deemed effective upon receipt if delivered by hand or telephone or
given by facsimile, one (1) Business Day after delivery to a reputable overnight
courier service and three (3) Business Days after being deposited in the mails.
The term "Business Day" shall mean a day on which the Bank's offices in Boston,
Massachusetts are open for business.

     (d)  This Agreement and the Guaranty shall be binding upon and inure to the
benefit of the Customer and the Bank and their respective successors and
assigns. The invalidity or unenforceability of any one or more phrases, clauses
or sections of this Agreement or the Guaranty shall not affect the validity or
enforceability of the remaining portions of this Agreement or the Guaranty. This
Agreement and the Guaranty are intended to take effect as a sealed instrument
and shall be construed in accordance with and governed by the laws (other than
the conflict of laws rules) of Massachusetts.

     Please indicate below your concurrence in the terms of this Agreement and
your acceptance of the Guaranty.

                                          STAPLES, INC.

                                          By____________________________

                   13
<PAGE>

Agreed and accepted:

BOSTON SAFE DEPOSIT & TRUST COMPANY

By_____________________________________

                                       14
<PAGE>

                                    EXHIBIT A

                                 TERM LOAN NOTE

Maximum Principal Amount:                            Date:_________, 2000
$_____________________                               Boston, Massachusetts

     On January 31, 2002, for value received, the undersigned, jointly and
severally if more than one ("Borrower"), promise to pay to the order of BOSTON
SAFE DEPOSIT AND TRUST COMPANY (the "Bank") at such place as the Bank may from
time to time designate, the aggregate principal amount outstanding on such date,
or earlier if demand is made for payment following default, with interest
thereon and any fees, expenses and charges, as provided below. At no time shall
the outstanding principal amount borrowed exceed the maximum principal amount
described above. The entries on the records of the Bank, including any appearing
on this Term Loan Note ("this Note"), will be prima facie evidence of the
aggregate principal amount outstanding under this Note, the interest accrued on
such amount and other fees and charges due.

     All payments hereunder including any prepayments of principal shall be
applied first to unpaid accrued interest, then to other fees, expenses and
charges due, including collection costs, and the balance, if any, to principal.
Principal repaid may not be reborrowed.

INTEREST

     Interest shall accrue at a floating annual rate equal to the rate quoted as
"Call Money" from time to time in the "Money Rates" section of The Wall Street
Journal, or if no such rate is quoted or The Wall Street Journal is not
available, the generally prevailing rate for loans to members of the New York
Stock Exchange secured by stock exchange collateral provided by Reuters or a
similar source of recognized standing selected by the Bank. In the event Bank
determines that for any reason no rate comparable to Call Money is available on
a given day, the Loans shall bear interest on such date at the Prime Rate (as
hereinafter defined) minus 1% per annum. "Prime Rate" shall mean the rate quoted
as the "Prime Rate" in the "Money Rates" section of The Wall Street Journal. In
the event "Call Money" or the "Prime Rate" is reported as a range of rates, the
rate used to calculate the interest rates under this Note will be the highest
such rate reported. The interest rate of this Note will change on the date
reported in The Wall Street Journal as the effective date of the change in Call
Money or the Prime Rate.

     In the event the interest rate indices stated above cease to be available,
the Bank may substitute any similar index, whether reported in The Wall Street
Journal or

<PAGE>

any other newspaper, and the Bank's selection shall be conclusive and binding on
the Borrower. In such event, and until the Bank selects a substitute index,
interest shall accrue at the rate in effect at the time the index in question
was determined by the Bank to be unavailable.

     Interest will begin to accrue on the day any proceeds of loans made under
this Note are disbursed. Interest will continue to accrue at the rate described
above, both before and after demand for payment, on the outstanding principal
until all principal amounts have been paid in full. The rate of interest shall
never exceed the maximum rate allowable under applicable law.

     Interest will be calculated on the basis of actual days elapsed in a 360
day year and will be payable in arrears. The first interest payment will be due
on the first day of the month immediately following any advance hereunder.
Subsequent interest payments will be due on the same day of every month
thereafter.

INTEREST PAYMENT OPTIONS

Borrower chooses to make monthly interest payments as indicated below:

     Payment Method #1: Borrower authorizes Bank to take payments out of
     Borrower's Checking Account maintained with Boston Safe Deposit and Trust
     Company, number ------------, titled -------------------, on or after the
     first business day of each month. Borrower will keep a large enough balance
     in this account to cover the full amount of the required payments.

     Payment Method #2: Bank will send Borrower a bill each month, and Borrower
     will mail or deliver the required payment so that Bank will receive it no
     later than the first day of each month.

     Payment Method #3: Borrower authorizes Bank to take payments out of either
     the principal or income or both of Borrower's Investment Account, number
     -------------, titled ------------------, on or after the first business
     day of each month. Borrower will maintain this Investment Account, in order
     to ensure that there are sufficient funds or assets in the Investment
     Account in order to meet Borrower's monthly payments.

     Borrower may request in writing a change in the Payment Option at any time.

                                       ii
<PAGE>

LATE CHARGES AND OTHER CHARGES

     In the event any payment of interest required to be made hereunder is not
made within 15 calendar days of the first day of each month, the date it is due,
the Borrower shall pay a late charge to the Bank of 5% of the amount due or $25,
whichever is greater. This charge must be paid within 30 days of the date it is
assessed and will be charged only once on each late payment.

     If any amount due as the principal of this Note is not paid in full on or
within five business days of the date of demand, such amount shall thereafter
bear interest payable on demand at a fluctuating rate per annum equal to the
greater of: (a) two percent (2%) above the Call Money rate (or one percent (1%)
above the Prime Rate, if the Call Money rate is unavailable) in effect on such
due date, or (b) two percent (2%) above the Call Money rate (or one percent (1%)
above the Prime Rate, if the Call Money rate is unavailable) in effect from time
to time thereafter.

     If due to either (i) the introduction of or any change in or in the
interpretation of any law or regulation or (ii) the compliance with any
guideline or request from any central bank or other governmental authority
(whether or not having the force of law), in each case after the date of this
Note, there shall be any increase in the cost to the Bank of agreeing to make or
making, funding or maintaining any loan under this Note (excluding any such
increased costs resulting from changes in the basis of taxation of overall net
income or overall gross income of the Bank by the United States or any political
subdivision thereof), then the Borrower shall, from time to time, within 5
business days after demand by the Bank, pay to the Bank additional amounts
sufficient to compensate the Bank for such increased costs.

     If the Bank determines that compliance with any law or regulation or any
guideline or request from any central bank or other governmental authority
(whether or not having the force of law) introduced or changed after the date of
this Note affects the amount of capital required to be maintained by the Bank
and that the amount of such capital is increased by or based upon the existence
of the Bank's loans hereunder, then, within 5 business days after demand by the
Bank, the Borrower shall pay to the Bank additional amounts sufficient to
compensate the Bank in the light of such circumstances.

     Bank shall notify the Borrower promptly after the occurrence of any event
described in the two immediately preceding paragraphs, and Borrower's liability
to Bank pursuant to such subsections shall be limited to amounts accruing after
the date of such notice. Demand by the Bank pursuant to such paragraphs shall be
accompanied by a certificate as to the amount of such increased cost or required
capital, respectively, showing calculations of the amount claimed in reasonable
detail. Bank's determination of any such increased cost (using any reasonable
method of averaging, attribution or

                                      iii
<PAGE>

allocation), as set forth in such a certificate shall, if correctly calculated,
be deemed prima facie evidence of such amount.

WIRE TRANSFER AUTHORIZATION

     Borrower hereby authorizes the Bank to wire transfer funds upon Borrower's
telephone, oral or written request, and agrees to hold the Bank harmless from
any and all claims, liabilities or damages, including reasonable attorney's fees
arising directly or indirectly from this authorization. The Bank shall be under
no obligation to verify the authenticity of any transfer request purporting or
which the Bank reasonably believes to be made by Borrower.

PREPAYMENT

     At any time or times before the maturity of this Note, whether as stated or
following acceleration as provided below, Borrower may make partial payments of
principal without penalty. All payments shall be made to the Bank's loan
servicing center in Pittsburgh, Pennsylvania, or at such other place as the Bank
may from time to time designate in writing.

SECURITY INTEREST DISCLOSURE

     As security for payment of this Note and the obligations provided for
herein, Borrower gives Lender a security interest in all the assets more fully
described in a Pledge Agreement of the Borrower previously or contemporaneously
delivered to Bank, and any modifications thereof (the "Pledge Agreement").

DEFAULT

     The following shall constitute Defaults hereunder:

          (i)  Default in the payment or performance of any obligation of the
Borrower to the Bank or the occurrence of a default under the Pledge Agreement.

          (ii) Death of the Borrower.

          (iii) If the Borrower shall cease to be an employee of Staples, Inc.
("Staples").

          (iv) If Staples shall notify Bank that the Borrower is no longer
eligible to participate in Staple's program of obtaining loans pursuant to this
Note.

          (v)  If the Borrower shall become the subject of any investigative or

                                       iv
<PAGE>

administrative proceeding or any civil or criminal action alleging violation of
state or federal securities laws.

          (vi) If Borrower shall sell or transfer all or substantially all of
his or her assets, or become insolvent, or fail generally to pay his or her
debts as they become due, or if a receiver is appointed for the Borrower or any
part of the property of the Borrower or if the Borrower shall make an assignment
or grant a trust mortgage for the benefit of (or composition with) the
creditors, or if a material adverse change shall occur in the financial
condition of the Borrower.

          (vii) The filing of a petition in bankruptcy by or against the
Borrower or the commencement of any proceedings by or against the Borrower under
any insolvency or other laws relating to the relief of debtors; or the taking of
any action by the Borrower to accomplish any of the foregoing.

     Upon the occurrence of a Default all of the obligations of the Borrower to
the Bank shall become immediately due and payable, without demand, presentment
or notice, notwithstanding any prior acceptance by Bank of periodic payments of
interest on this Note or such other Obligations.

SETOFF DISCLOSURE

     To the extent permitted by law, the Bank has the right to apply funds from
any deposit account(s) of Borrower or cosigner with the Bank to pay all or any
portion of any amount outstanding under this Note or otherwise to the Bank.

     In addition to any right of setoff given to the Bank by law against any
property of Borrower, the Bank shall have a lien on and security interest in all
property of Borrower now or hereafter on deposit with the Bank. Such lien and
security interest may be enforced without demand upon or notice to Borrower,
shall continue in full force unless specifically waived or released by the Bank
in writing, and shall not be deemed waived by any delay of the Bank in enforcing
the lien or security interest.

COLLECTION COSTS

     Borrower promises to pay on demand, to the extent permitted under
applicable law, all costs and expenses, including reasonable attorneys' fees,
incurred or paid by the Bank in enforcing this Note, whether or not litigation
is commenced, and in selling or otherwise disposing of all or any part of any
property pledged to secure this Note. All such costs and expenses shall be
secured by such collateral.

                                       v
<PAGE>

JOINT LIABILITY

     If more than one person has signed this Note, their obligations shall be
joint and several, and the liability of each shall be absolute and unconditional
and without regard to the liability of any other party hereto.

WAIVER

     Unless prohibited by applicable law, Borrower, all co-Borrowers, any
endorser and any other party hereto, and each of them (1) waives presentment,
demand, notice, protest, and all other demands and notices in connection with
the delivery, acceptance, performance, default or enforcement of this Note or of
any document or instrument evidencing any security for the payment of this Note,
except for demand for payment hereunder and any notices provided for in the
Pledge Agreement; (2) assents to any one or more extensions or postponements of
the time of payment or any other indulgences, to any additions or substitutions,
exchanges or releases of collateral and/or the addition, substitution or release
of any one or more parties or persons primarily or secondarily liable hereunder,
and (3) agrees that no such action, failure to act or failure to exercise any
right or remedy, on the part of the Bank shall in any way affect or impair the
obligations of any of them or be construed as a waiver by Bank of, or otherwise
affect, any of Bank's rights under this Note, under any endorsement or guaranty
of this Note or under any document or instrument evidencing any security for
payment of this Note. No delay or omission by the Bank in exercising in whole or
in part any right or remedy hereunder shall operate as a waiver thereof or of
any other right or remedy. A waiver of any right or remedy, in whole or in part,
on any one occasion shall not be construed as a bar to enforcing or as a waiver
of that or any other right or remedy on any future occasion.

ADDRESS CHANGE

     Borrower shall notify the Bank of any change in the Borrwer's address of
record. Any such notice shall be directed to the Bank at the address for
payments, or to such other address as the Bank may direct. In the event such
notice is not given by the Borrower, Borrower shall be deemed to have waived the
right to receive any notice which otherwise would be required under this Note or
by applicable law, unless such waiver is specifically prohibited by applicable
law or regulation.

ENTIRE AGREEMENT

     The terms and conditions of the Pledge Agreement are deemed to be
incorporated herein by reference. Such terms and conditions, together with the
terms and conditions of this Note, constitute the entire agreement of the
parties and

                                       vi

<PAGE>

supersede all prior agreements and understandings, both written and oral, of
the parties hereto with respect to the subject matter of this Note or of any
such agreement. The captions and headings of the various sections of this Note
are for convenience only and are not to be considered as defining or limiting,
in any way the scope or intent of the provisions hereof. Neither this Note nor
such Pledge Agreement may be modified or amended except by a writing signed by
the Bank.

FINANCIAL INFORMATION/FURTHER DOCUMENTS

     At Bank's request, Borrower will give Bank a completed and signed personal
financial statement in such form as Bank may require. Borrower will execute any
documents or instruments required by Bank to perfect its security interest or as
otherwise may be required by Bank, as Bank may request from time to time.

GENERAL PROVISIONS

     This Note inures to the benefit of the Bank and to the benefit of its
successors and assigns. This Note is binding on each Borrower and on any
executor, administrator or legal representative of any Borrower.

     No security interest granted to the Bank by Borrower in any dwelling of any
Borrower shall secure payment of this Note unless specific reference is made to
this Note. Other collateral securing other obligations of Borrower to the Bank
may also secure this Note.

GOVERNING LAW

     This Note will take effect as a sealed instrument and will be governed by
and construed in accordance with the laws of the Commonwealth of Massachusetts.
If any provision of this Note is deemed to be in conflict with applicable law,
it will considered to be modified to comply with the law or, if not capable of
such modification, such provision will be deemed to be deleted from this Note.
Notwithstanding any such modification or deletion, the remaining provisions will
remain valid and enforceable.

                                      vii
<PAGE>

BY SIGNING BELOW, BORROWER AGREES TO THE TERMS OF THIS AGREEMENT.

__________________________________________
Borrower                            (Seal)

BORROWER'S ADDRESS OF RECORD:

__________________________________________
         Print Name

__________________________________________
Address

__________________________________________
City                 State                Zip Code

                                      viii<PAGE>

EXHIBIT 10.51

December 7, 1999

Stuart J.M. Collinson, Ph.D.
11010 Torreyana Rd.
San Diego, CA 92121

RE:      EMPLOYMENT TERMS

Dear Stuart:

This letter ("Agreement") sets forth the agreement between you and Aurora
Biosciences Corporation (the "Company") regarding the terms of your employment
as President and Chief Executive Officer of the Company. You and the Company
hereby agree as follows:

You will serve as President and Chief Executive Officer and will be responsible
for such duties as are normally associated with such position or as otherwise
determined by the Company's Board of Directors ("Board"). You will be subject to
the direction and policies from time to time reasonably established by the
Board. You will work out of our principal offices located in San Diego. You will
devote your full business energies, abilities and productive time to the proper
and efficient performance of your duties for the Company.

You shall receive an initial base salary of $350,000 per year, payable in
regular periodic payments in accordance with Company policy, less required
payroll deductions and withholdings. Your base salary will be subject to
increases as determined by the Board.

You will be eligible for an annual performance bonus paid in cash of up to
fifty percent (50%) of your base salary based on your achievement of
specified milestones as mutually agreed upon in good faith by the Board and
you within a reasonable period of time following execution of this Agreement.

Effective as of the date hereof, you will be granted an Incentive Stock Option
to purchase eighty thousand (80,000) shares of the Common Stock of the Company
(the "Option") pursuant to the terms of the Company's 1996 Stock Plan (the
"Plan"). The exercise price per share of the shares subject to the Option will
be at the fair market value of the Company's Common Stock on the date hereof as
determined in accordance with the Plan. Subject to the terms of the Plan and the
provisions of this Agreement set forth below, your Option will vest over four
(4) years so long as you continue to be employed with the Company, according to
the following schedule: twenty thousand (20,000) shares will vest as of the
first anniversary of the date hereof and the remaining sixty thousand (60,000)
shares will vest in equal monthly installments over a period of thirty-six (36)
months beginning after such one year anniversary.

The Company will continue to provide you with a competitive comprehensive
benefits package including medical, dental, life and disability insurance. In
addition to the

<PAGE>

foregoing, you will receive all other benefits the Company may provide from time
to time to other senior executive level employees.

Although the Company's policy provides 17 days of Paid Personal Leave (PPL),
you will accrue vacation, regardless of your length of service, at the rate of
20 days per year. If the Company elects to close operations between Christmas
and New Year's, this time off will be considered paid holiday time and will
not count against the 20 days of paid personal leave.

The Company will continue to reimburse you for your reasonable travel,
entertainment, business and other expenses incurred in the course of your
employment in accordance with Company policy.

Your employment with the Company will continue to be "at-will", meaning that you
may terminate your employment with the Company at any time and for any reason
whatsoever, with or without advance notice and likewise, the Company, may
terminate your employment at any time and for any reason whatsoever, with or
without advance notice. This at-will arrangement may not be changed except by a
writing signed by you and a duly authorized officer of the Company.

Upon termination of your employment with the Company, you will be paid your then
current accrued base salary to and including the date of termination, any
accrued vacation pay and other benefits through the date of termination and all
compensation previously deferred by you, if any (together with accrued interest
and earnings thereon).

Notwithstanding the foregoing, if the Company terminates your employment without
"Cause" (defined below) or you resign for "Good Reason" (defined below), then
upon your (or your representatives) furnishing to the Company an executed
release and waiver of claims in the form attached hereto as Exhibit A (the
"Release") and the occurrence of the Release Effective Date provided for in the
Release (the "Release Effective Date"), the Company shall pay to you the
following: (1) a lump sum equal to one (1) year of your then current base salary
plus an amount equal to your most recent annual bonus, subject to standard
payroll deductions and withholdings; (2) to the extent any Company stock options
then held by you are unvested, the vesting of such options and stock shall be
accelerated and such options shall become fully vested and immediately
exercisable; and (3) the Company will reimburse you for actual and reasonable
expenses incurred by you in connection with relocation of your principal
residence to the United Kingdom. Such reimbursement will be available to you
during the six (6) months following termination of your employment. Items that
are eligible for reimbursement include the actual and reasonable costs of moving
household goods (packing and moving expenses), storage, home sale and home
purchase closing costs; and (4) any outstanding housing loan you have with the
Company will be forgiven by the Company such that the principal and interest due
on such loan will be zero as of the date of termination. You understand that the
Company has not made any representations regarding the tax consequences of the
benefits it has promised to provide you pursuant to this Agreement and
recommends that you seek separate advice from a tax advisor.

If you resign without Good Reason, do not furnish to the Company an executed
release or the Release Effective Date does not occur, or your employment is
terminated for Cause, all compensation and benefits will cease immediately, and
you will receive no severance benefits. You will receive your current accrued
base salary and any accrued benefits through the date of termination, as well as
any reimbursement expenses due to you for which you shall not have been
previously reimbursed.

<PAGE>

For purposes of this Agreement the following definitions shall apply:

         (1) "Cause" shall be limited to the occurrence of any of the following
events: (i) your personally engaging in illegal conduct which causes material
harm to the reputation of the Company, (ii) your being convicted or found liable
for a felony, misdemeanor or gross misconduct relating to an act of dishonesty
or fraud against, or a misappropriation of property belonging to the Company,
(iii) your refusal to substantially perform duties set forth in a specific
resolution by the Board, or (iv) your incurable breach of any material element
of the Company's Proprietary Information and Inventions Agreement;

         (2) "Good Reason" shall mean (i) a reduction in your base salary or
potential Bonus, or any material reduction in benefits; (ii) the relocation of
your full-time office to a location other than in San Diego County; (iii) a
substantial reduction in your duties inconsistent with your status as President
and Chief Executive Officer; or (iv) any reason or no reason following the
occurrence of a Change in Control (as defined in the Plan) of the Company.

As a Company employee, you will be expected to continue to abide by Company
rules and regulations.

This Agreement supersedes any other agreements or promises made to you by
anyone, whether oral or written, and comprise the final, complete and exclusive
agreement between you and the Company. Without limiting the foregoing, this
Agreement supersedes the letter agreement dated April 29, 1999 between the
Company and you, which is hereby terminated and of no further force or effect.
As required by law, this offer is subject to satisfactory proof of your
continuing right to work in the United States.

Please sign and date this Agreement, and return it to me as soon as possible if
you wish to accept the terms described above.

Sincerely,

AURORA BIOSCIENCES CORPORATION

By:      /s/ JOHN D. MENDLEIN
   --------------------------------------------------------
         John D. Mendlein
         Senior Vice President, Intellectual Property, General
         Counsel and Chief Knowledge Officer

ACCEPTED BY:

      /s/ STUART J.M. COLLINSON
-----------------------------------------------------
         Stuart JM Collinson, Ph.D.

   December 7, 1999
-----------------------
         Date

<PAGE>

                                    EXHIBIT A

                          RELEASE AND WAIVER OF CLAIMS

         In consideration of the severance payments and other benefits set forth
in the Agreement dated ___________, 1999, to which this form is attached, I,
STUART JM COLLINSON, hereby furnish AURORA BIOSCIENCES CORPORATION (the
"COMPANY"), with the following release and waiver ("RELEASE AND WAIVER").

         I hereby release, and forever discharge the COMPANY, its officers,
directors, agents, employees, stockholders, successors, assigns affiliates and
Benefit Plans, of and from any and all claims, liabilities, demands, causes of
action, costs, expenses, attorneys' fees, damages, indemnities and obligations
of every kind and nature, in law, equity, or otherwise, known and unknown,
suspected and unsuspected, disclosed and undisclosed, arising at any time prior
to and including my employment TERMINATION DATE with respect to any claims
relating to my employment and the termination of my employment, including but
not limited to, claims pursuant to any federal, state or local law relating to
employment, including, but not limited to, discrimination claims, claims under
the California Fair Employment and Housing Act, and the Federal Age
Discrimination in Employment Act of 1967, as amended ("ADEA"), or claims for
wrongful termination, breach of the covenant of good faith, contract claims,
tort claims, and wage or benefit claims, including but not limited to, claims
for salary, bonuses, commissions, stock, stock options, vacation pay, fringe
benefits, severance pay or any form of compensation.

         I also acknowledge that I have read and understand Section 1542 of the
California Civil Code which reads as follows: "A GENERAL RELEASE DOES NOT EXTEND
TO CLAIMS WHICH THE CREDITOR DOES NOT KNOW OR SUSPECT TO EXIST IN HIS FAVOR AT
THE TIME OF EXECUTING THE RELEASE, WHICH IF KNOWN BY HIM MUST HAVE MATERIALLY
AFFECTED HIS SETTLEMENT WITH THE DEBTOR." I hereby expressly waive and
relinquish all rights and benefits under that section and any law of any
jurisdiction of similar effect with respect to any claims I may have against the
Company.

         I acknowledge that, among other rights, I am waiving and releasing any
rights I may have under ADEA, that this RELEASE AND WAIVER is knowing and
voluntary, and that the consideration given for this RELEASE AND WAIVER is in
addition to anything of value to which I was already entitled as an executive of
the COMPANY. I further acknowledge that I have been advised, as required by the
Older Workers Benefit Protection Act, that: (a) the RELEASE AND WAIVER granted
herein does not relate to claims which may arise after this RELEASE AND WAIVER
is executed; (b) I have the right to consult with an attorney prior to executing
this RELEASE AND WAIVER (although I may choose voluntarily not to do so); and if
I am 40 years or older upon execution of this RELEASE AND WAIVER: (c) I have
twenty-one (21) days from the date of termination of my employment with the
COMPANY in which to consider this RELEASE AND WAIVER (although I may choose
voluntarily to execute this RELEASE AND WAIVER earlier); (d) I have seven (7)
days following the execution of this RELEASE AND WAIVER to revoke my consent to
this RELEASE AND WAIVER; and (e) this RELEASE AND WAIVER shall not be effective
until the seven (7) day revocation period has expired (the "Release Effective
Date").

Date:                                      By:    /s/ Stuart J.M. Collinson
      ------------------                       --------------------------------

                                       2.

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