SECOND LOAN MODIFICATION AGREEMENT

         This SECOND LOAN MODIFICATION AGREEMENT is entered into as of August
27, 1997, by and between SILICON VALLEY BANK, a California-chartered bank with
its principal place of business at 3003 Tasman Drive, Santa Clara, CA 95054 and
with a loan production office located at Wellesley Office Park, 40 William
Street, Suite 350, Wellesley, MA 02181, doing business under the name "Silicon
Valley East ("Bank"), and ENDOGEN, INC., a MASSACHUSETTS corporation with its
principal place of business at 30 COMMERCE WAY, WOBURN, MASSACHUSETTS 01801
("Borrower").

                                    RECITALS

         Borrower has borrowed money from Bank pursuant to certain Existing Loan
Documents, as defined below. In consideration of certain financial
accommodations from Bank, and Borrower's continuing obligations under the
Existing Loan Documents, Borrower and Bank agree as follows:

                                    AGREEMENT

         1. DESCRIPTION OF EXISTING INDEBTEDNESS. Among other indebtedness which
may be owing by Borrower to Bank, Borrower is indebted to Bank pursuant to a
Revolving Promissory Note dated August 28, 1996 in the original principal amount
of EIGHT HUNDRED FIFTY THOUSAND AND NO/100THS DOLLARS ($850,000) (the "Revolving
Note") and a Term Promissory Note dated August 28, 1996 in the original
principal amount of FOUR HUNDRED THOUSAND AND NO/100THS DOLLARS ($400,000) (the
"Term Note"). The Revolving Note and the Term Note are governed by the terms of
a Loan and Security Agreement dated August 28, 1996 between Borrower and Bank,
as amended by a Loan Modification Agreement dated as of May 7, 1997 between
Borrower and Bank, and as such Loan and Security Agreement may be further
amended from time to time (the "Loan Agreement").

         Hereinafter, all indebtedness owing by Borrower to Bank under the
Revolving Note, the Term Note and the Loan Agreement shall be referred to as the
"Indebtedness."

         2. DESCRIPTION OF COLLATERAL. Repayment of the Indebtedness is secured
pursuant to the Loan Agreement. Hereinafter, the Loan Agreement, the Revolving
Note and the Term Note, together with all other documents securing payment of
the Indebtedness, shall be referred to as the "Existing Loan Documents."

         3.       DESCRIPTION OF CHANGES IN TERMS.

         3.1      Modifications to Revolving Note.  The Revolving Note is hereby
                  amended as follows:

                  The entire principal amount and all accrued interest shall be
due and payable on AUGUST 26, 1998.

         3.2 Modifications to Definitions. Section 1.1 of the Loan Agreement is
hereby amended by substituting the following definitions for those set forth
therein for the same terms, and in the case of new definitions, by adding those
new definitions to that Section 1.1:

                  "Committed Equipment Line" means a credit extension of up to
                  TWO HUNDRED FIFTY THOUSAND AND NO/100THS Dollars ($250,000)

                  "Credit Extension" means each Advance, Equipment Advance,
                  Letter of Credit, Exchange Contract or any other extension of
                  credit by Bank for the benefit of Borrower hereunder.

                  "Equipment Advance" has the meaning set forth in Section 
                  2.1.4.


                                       1


<PAGE>

                  "Equipment Availability End Date" has the meaning set forth in
                  Section 2.1.4.

                  "Exchange Contract" has the meaning set forth in Section 
                  2.1.3.

                  "Letter of Credit" means a letter of credit or similar
                  undertaking issued by Bank pursuant to Section 2.1.2.

                  "Letter of Credit Reserve" has the meaning set forth in 
                  Section 2.1.2.

                  "Maturity Date" means March 27, 2001.

                  "Revolving Maturity Date" means August 26, 1998.

         3.3      Modifications to Section 2.1 of Loan Agreement. Section 2.1 
                  of the Loan Agreement is hereby replaced in its entirety
                  with the following

                  2.1 Credit Extensions. Borrower promises to pay to the order
                  of Bank, in lawful money of the United States of America, the
                  aggregate unpaid principal amount of all Credit Extensions
                  made by Bank to Borrower hereunder. Borrower shall also pay
                  interest on the unpaid principal amount of such Credit
                  Extensions at rates in accordance with the terms hereof.

                  2.1.1    Revolving Advances.

                  (a) Subject to and upon the terms and conditions of this
                  Agreement, Bank agrees to make Revolving Advances to Borrower
                  in an aggregate outstanding amount not to exceed (i) the
                  Committed Revolving Line or the Borrowing Base, whichever is
                  less, (ii) minus, the face amount of all outstanding Letters
                  of Credit (including drawn but unreimbursed Letters of
                  Credit), and (iii) minus the Foreign Exchange Reserve. Subject
                  to the terms and conditions of this Agreement, amounts
                  borrowed pursuant to this Section 2.1.1 may be repaid and
                  reborrowed at any time up to the Revolving Maturity Date.

                  (b) Whenever Borrower desires a Revolving Advance, Borrower
                  will notify Bank by facsimile transmission or telephone no
                  later than 3:00 p.m. Pacific time, on the Business Day that
                  the Revolving Advance is to be made. Each such notification
                  shall be promptly confirmed by a Payment/Advance Form in
                  substantially the form of Exhibit B hereto. Bank is authorized
                  to make Revolving Advances under this Agreement, based upon
                  instructions received from a Responsible Officer or a designee
                  of a Responsible Officer, or without instructions if in Bank's
                  discretion such Revolving Advances are necessary to meet
                  Obligations which have become due and remain unpaid. Bank
                  shall be entitled to rely on any telephonic notice given by a
                  person who Bank reasonably believes to be a Responsible
                  Officer or a designee thereof, and Borrower shall indemnify
                  and hold Bank harmless for any damages or loss suffered by
                  Bank as a result of such reliance. Bank will credit the amount
                  of Revolving Advances made under this Section 2.1 to
                  Borrower's deposit account.

                  (c) The Committed Revolving Line shall terminate on the
                  Revolving Maturity Date, at which time all Revolving Advances
                  under this Section 2.1.1 and other amounts due under this
                  Agreement (except as otherwise expressly specified herein)
                  shall be immediately due and payable.


                                       2

<PAGE>

                  2.1.2    Letters of Credit.

                  (a) Subject to the terms and conditions of this Agreement,
                  Bank agrees to issue or cause to be issued Letters of Credit
                  for the account of Borrower in an aggregate outstanding face
                  amount not to exceed (i) the lesser of the Committed Revolving
                  Line or the Borrowing Base, whichever is less, (ii) minus the
                  then outstanding principal balance of the Advances; provided
                  that the face amount of outstanding Letters of Credit
                  (including drawn but unreimbursed Letters of Credit and any
                  Letter of Credit Reserve) shall not in any case exceed TWO
                  HUNDRED FIFTY THOUSAND AND NO/100THS Dollars ($250,000). Each
                  Letter of Credit shall have an expiry date no later than three
                  hundred sixty (360) days after the Revolving Maturity Date,
                  provided that Borrower's Letter of Credit reimbursement
                  obligation shall be secured by cash on terms acceptable to
                  Bank at any time after the Revolving Maturity Date if the term
                  of this Agreement is not extended by Bank. All Letters of
                  Credit shall be in form and substance acceptable to Bank in
                  its sole discretion and shall be subject to the terms and
                  conditions of Bank's form of standard Application and Letter
                  of Credit Agreement.

                  (b) The obligation of Borrower to immediately reimburse Bank
                  for drawings made under Letters of Credit shall be absolute,
                  unconditional and irrevocable, and shall be performed strictly
                  in accordance with the terms of this Agreement and such
                  Letters of Credit, under all circumstances whatsoever.
                  Borrower shall indemnify, defend, protect and hold Bank
                  harmless from any loss, cost, expense or liability, including,
                  without limitation, reasonable attorneys' fees, arising out of
                  or in connection with any Letters of Credit.

                  (c) Borrower may request that Bank issue a Letter of Credit
                  payable in a currency other than United States Dollars. If a
                  demand for payment is made under any such Letter of Credit,
                  Bank shall treat such demand as an Advance to Borrower of the
                  equivalent of the amount thereof (plus cable charges) in
                  United States currency at the then prevailing rate of exchange
                  in San Francisco, California, for sales of that other currency
                  for cable transfer to the country of which it is the currency.

                  (d) Upon the issuance of any Letter of Credit payable in a
                  currency other than United States Dollars, Bank shall create a
                  reserve under the Committed Revolving Line for letters of
                  credit against fluctuations in currency exchange rates, in an
                  amount equal to ten percent (10%) of the face amount of such
                  Letter of Credit (the "Letter of Credit Reserve"). The amount
                  of such Letter of Credit Reserve may be amended by Bank from
                  time to time to account for fluctuations in the exchange rate.
                  The availability of funds under the Committed Revolving Line
                  shall be reduced by the amount of such Letter of Credit
                  Reserve for so long as such Letter of Credit remains
                  outstanding.

                  2.1.3    Foreign Exchange Contract; Foreign Exchange 
                           Settlements.

                  (a) Subject to the terms of this Agreement, Borrower may enter
                  into foreign exchange contracts (the "Exchange Contracts") not
                  to exceed an aggregate amount of TWO HUNDRED FIFTY THOUSAND


                                       3

<PAGE>

                  AND NO/100THS Dollars ($250,000) (the "Contract Limit"),
                  pursuant to which Bank shall sell to or purchase from Borrower
                  foreign currency on a spot or future basis. Borrower shall not
                  request any Exchange Contracts at any time it is out of
                  compliance with any of the provisions of this Agreement. All
                  Exchange Contracts must provide for delivery or settlement on
                  or before the Revolving Maturity Date. The amount available
                  under the Committed Revolving Line at any time shall be
                  reduced by the following amounts (the "Foreign Exchange
                  Reserve") on any given day (the "Determination Date"): (i) on
                  all outstanding Exchange Contracts on which delivery is to be
                  effected or settlement allowed more than two business days
                  after the Determination Date, 10% of the gross amount of the
                  Exchange Contracts; plus (ii) on all outstanding Exchange
                  Contracts on which delivery is to be effected or settlement
                  allowed within two business days after the Determination Date,
                  100% of the gross amount of the Exchange Contracts.

                  (b) Bank may, in its discretion, terminate the Exchange
                  Contracts at any time (a) that an Event of Default occurs or
                  (b) that there is no sufficient availability under the
                  Committed Revolving Line and Borrower does not have available
                  funds in its bank account to satisfy the Foreign Exchange
                  Reserve. If Bank terminates the Exchange Contracts, and
                  without limitation of any applicable indemnities, Borrower
                  agrees to reimburse Bank for any and all fees, costs and
                  expenses relating thereto or arising in connection therewith.

                  (c) Borrower shall not permit the total gross amount of all
                  Exchange Contracts on which delivery is to be effected and
                  settlement allowed in any two business day period to be more
                  than $100,000 (the "Settlement Limit") nor shall Borrower
                  permit the total gross amount of all Exchange Contracts to
                  which Borrower is a party, outstanding at any one time, to
                  exceed the Contract Limit. Notwithstanding the above, however,
                  the amount which may be settled in any two (2) business day
                  period may be increased above the Settlement Limit up to, but
                  in no event to exceed, the amount of the Contract Limit under
                  either of the following circumstances:

                  (i) if there is sufficient availability under the Committed
                  Revolving Line in the amount of the Foreign Exchange Reserve
                  as of each Determination Date, provided that Bank in advance
                  shall reserve the full amount of the Foreign Exchange Reserve
                  against the Committed Revolving Line; or

                  (ii) if there is insufficient availability under the Committed
                  Revolving Line, as to settlements within any two (2) business
                  day period, provided that Bank, in its sole discretion, may:
                  (A) verify good funds overseas prior to crediting Borrower's
                  deposit account with Bank (in the case of Borrower's sale of
                  foreign currency); or (B) debit Borrower's deposit account
                  with Bank prior to delivering foreign currency overseas (in
                  the case of Borrower's purchase of foreign currency).

                  (d) In the case of Borrower's purchase of foreign currency,
                  Borrower in advance shall instruct Bank upon settlement either
                  to treat the settlement amount as an advance under the
                  Committed Revolving Line, or to debit Borrower's account for
                  the amount settled.

                  (e) Borrower shall execute all standard form applications and
                  agreements of Bank in connection with the Exchange Contracts


                                       4

<PAGE>

                  and, without limiting any of the terms of such applications
                  and agreements, Borrower will pay all standard fees and
                  charges of Bank in connection with the Exchange Contracts.

                  (f) Without limiting any of the other terms of this Agreement
                  or any such standard form applications and agreement of Bank,
                  Borrower agrees to indemnify Bank and hold it harmless, from
                  and against any and all claims, debts, liabilities, demands,
                  obligations, actions, costs and expenses (including, without
                  limitation, attorneys' fees of counsel of Bank's choice), of
                  every nature and description which it may sustain or incur,
                  based upon, arising out of, or in any way relating to any of
                  the Exchange Contracts or any transactions relating thereto or
                  contemplated thereby.

                  2.1.4    Equipment Advances.

                  (a) Subject to and upon the terms and conditions of this
                  Agreement, at any time from the date hereof through April 8,
                  1998 (the "Equipment Availability End Date"), Bank agrees to
                  make advances (each an "Equipment Advance" and collectively,
                  the "Equipment Advances") to Borrower in an aggregate
                  outstanding amount not to exceed the Committed Equipment Line.
                  To evidence the Equipment Advance or Equipment Advances,
                  Borrower shall deliver to Bank, at the time of each Equipment
                  Advance request, an invoice for the equipment to be purchased
                  or financed The Equipment Advances shall be used only to
                  purchase or finance Equipment purchased on or after June 1,
                  1997 and shall not exceed ONE HUNDRED Percent (100%) of the
                  invoice amount of such equipment approved from time to time by
                  Bank, excluding taxes, shipping, warranty charges, freight
                  discounts and installation expense. Software and tenant
                  improvements may, however, constitute up to TWENTY FIVE
                  percent (25%) and THIRTY FIVE percent (35%), respectively, of
                  aggregate Equipment Advances. (b) Interest shall accrue from
                  the date of each Equipment Advance at a per annum rate equal
                  to ONE AND ONE-QUARTER (1.25) percentage points above the
                  Prime Rate and shall be payable monthly for each month through
                  the month in which the Equipment Availability End Date falls.
                  Any Equipment Advances that are outstanding on the Equipment
                  Availability End Date will be payable in THIRTY SIX (36) equal
                  monthly installments of principal, plus all accrued interest,
                  beginning on the Payment Date of each month following the
                  Equipment Availability End Date and ending on the Maturity
                  Date. Equipment Advances, once repaid, may not be reborrowed.

                  (c) When Borrower desires to obtain an Equipment Advance,
                  Borrower shall notify Bank (which notice shall be irrevocable)
                  by facsimile transmission to be received no later than 3:00
                  p.m. Pacific time one (1) Business Day before the day on which
                  the Equipment Advance is to be made. Such notice shall be
                  substantially in the form of Exhibit B. The notice shall be
                  signed by a Responsible Officer or its designee and include a
                  copy of the invoice(s) for the Equipment to be financed.

         3.4      Modifications to Overadvances Provisions.  Section 2.3 of the
                  Loan Agreement is hereby replaced in its entirety with the
                  following:


                                       5
<PAGE>

                  2.3 Overadvances. If, at any time or for any reason, the
                  amount of Obligations owed by Borrower to Bank pursuant to
                  Sections 2.1.1, 2.1.2 and 2.1.3 of this Agreement is greater
                  than the Committed Revolving Line or the Borrowing Base,
                  whichever is less, then Borrower shall immediately pay to
                  Bank, in cash, the amount of such excess.

         3.5      Modifications to Interest Rate Provisions.  Sections 2.4(a) 
                  and (b) of the Loan Agreement are hereby replaced in their
                  entirety with the following:

                  (a) Interest Rate. Except as set forth in Section 2.4(b), all
                  Advances shall bear interest on the average Daily Balance at a
                  rate equal to ONE (1.0) percentage point above the Prime Rate;
                  and the Term Loan shall bear interest on the average Daily
                  Balance at a rate equal to ONE AND ONE-QUARTER (1.25)
                  percentage points above the Prime Rate.

                  (b) Default Rate. All Obligations shall bear interest, from
                  and after the occurrence, and during the continuance, of an
                  Event of Default, at a rate equal to five (5) percentage
                  points above the interest rate applicable immediately prior to
                  the occurrence of the Event of Default.

         3.6      Modifications to Term of Agreement.  Section 2.8 of the Loan 
                  Agreement is hereby replaced in its entirety with the 
                  following:

                  2.8 Term. Except as otherwise set forth herein, this Agreement
                  shall become effective on the Closing Date and, subject to
                  Section 12.7, shall continue in full force and effect for a
                  term ending on the Maturity Date. Notwithstanding the
                  foregoing, Bank shall have the right to terminate its
                  obligation to make Credit Extensions under this Agreement
                  immediately and without notice upon the occurrence, and during
                  the continuance, of an Event of Default. Notwithstanding
                  termination, Bank's Lien on the Collateral shall remain in
                  effect for so long as any Obligations are outstanding.

         3.7      Modifications to Financial Reporting Covenants.  Section 6.3 
                  of the Loan Agreement is hereby replaced in its entirety
                  with the following:

                  6.3      Financial Statements, Reports, Certificates.  (i) 
                           Borrower shall deliver to Bank:

                  (a) within five (5) days of filing with the SEC, copies of all
                  statements, reports and notices sent or made available
                  generally by Borrower to its security holders or to any
                  holders of Subordinated Debt and all reports on Form 10-K,
                  10-Q and 8-K filed with the Securities and Exchange
                  Commission;

                  (b) promptly upon receipt of notice thereof, a report of any
                  legal actions pending or threatened against Borrower or any
                  Subsidiary that could result in damages or costs to Borrower
                  or any Subsidiary of One Hundred Thousand Dollars ($100,000)
                  or more; and

                  (c) such budgets, sales projections, operating plans or other
                  financial information as Bank may reasonably request from time
                  to time.

                  (d) Within twenty-five (25) days after the last day of each
                  month, Borrower shall deliver to Bank a Borrowing Base


                                       6
<PAGE>

                  Certificate signed by a Responsible Officer in substantially
                  the form of Exhibit C hereto, together with aged listings of
                  accounts receivable and accounts payable.

                  (e) Within five (5) days filing its Form 10-Q with the SEC,
                  Borrower shall deliver to Bank, with the Form 10-Q, a
                  Compliance Certificate signed by a Responsible Officer in
                  substantially the form of Exhibit D hereto.

                  (ii) Bank shall have a right from time to time hereafter to
                  audit Borrower's Accounts at Borrower's expense, provided that
                  such audits will be conducted no more often than every twelve
                  (12) months unless an Event of Default has occurred and is
                  continuing.

         3.8      Modifications to Quick Ratio Covenant. Section 6.8 of the 
                  Loan Agreement is hereby replaced in its entirety with the
                  following:

                  6.8 Quick Ratio. Borrower shall maintain, as of the last day
                  of each fiscal quarter beginning with the fiscal quarter
                  ending August 31, 1997, a ratio of Quick Assets to Current
                  Liabilities of at least 1.10 to 1.0.

         3.9      Modifications to Debt-Net Worth Ratio Covenant.  Section 6.9 
                  of the Loan Agreement is hereby replaced in its entirety with
                  the following:

                  6.9 Debt-Net Worth Ratio. Borrower shall maintain, as of the
                  last day of each fiscal quarter beginning with the fiscal
                  quarter ending August 31, 1997, a ratio of Total Liabilities
                  less Subordinated Debt to Tangible Net Worth plus Subordinated
                  Debt of not more than 0.75 to 1.0.

         3.10     Modifications to Tangible Net Worth Covenant. Section 6.10 of
                  the Loan Agreement is hereby replaced in its entirety with
                  the following:

                  6.10 Tangible Net Worth. Borrower shall maintain, as of the
                  last day of each fiscal quarter beginning with the fiscal
                  quarter ending August 31, 1997, a Tangible Net Worth of not
                  less than FOUR MILLION AND NO/100THS Dollars ($4,000,000).

         3.11     Modifications to Profitability Covenant. Section 6.11 of the
                  Loan Agreement is hereby replaced in its entirety with the
                  following:

                  6.11 Profitability. Borrower shall be profitable for each
                  fiscal quarter beginning with the fiscal quarter ending August
                  31, 1997, except Borrower may suffer a loss no greater than
                  SEVENTY FIVE THOUSAND AND NO/100THS Dollars ($75,000) in any
                  one fiscal quarter in the fiscal year commencing October 1,
                  1997.

         3.10     Modifications to Debt Service Covenant. Section 6.12 of the 
                  Loan Agreement is hereby replaced in its entirety with the
                  following:

                  6.12 Minimum Debt Service. Borrower shall maintain, as of the
                  last day of each fiscal quarter beginning with the fiscal
                  quarter ending August 31, 1997, a Debt Service ratio of at
                  least 1.50 to 1.00.

         3.11     Modifications to Default Provisions. References to "Advances"
                  in Sections 8.2, 8.4, 8.5 and 8.8 of the Loan Agreement are 
                  hereby replaced with "Credit Extensions".

         3.12     Modifications to Bank's Rights and Remedies. Sections 
                  9.1(g)(1) and 9.1(g)(2) are hereby added to the Loan Agreement
                  as follows:


                                       7

<PAGE>

                  (g)(1) Demand that Borrower (i) deposit cash with Bank in an
                  amount equal to the amount of any Letters of Credit remaining
                  undrawn, as collateral security for the repayment of any
                  future drawings under such Letters of Credit, and Borrower
                  shall forthwith deposit and pay such amounts, and (ii) pay in
                  advance all Letters of Credit fees scheduled to be paid or
                  payable over the remaining term of the Letters of Credit;

                  (g)(2) Liquidate any Exchange Contracts not yet settled and
                  demand that Borrower immediately deposit cash with Bank in an
                  amount sufficient to cover any losses incurred by Bank due to
                  liquidation of the Exchange Contracts at the then prevailing
                  market price;

         3.13 Modifications to Exhibits. Exhibits C and D of the Loan Agreement
are hereby replaced in their entirety with Exhibits C and D to this Agreement.

         4. FACILITY FEE. Borrower shall pay to Bank a Facility Fee equal to
FIVE THOUSAND FIVE HUNDRED AND NO/100THS Dollars ($5,500), which fee shall be
due upon delivery of this Second Loan Modification Agreement to Bank and shall
be fully earned and non-refundable. as well as any out-of-pocket expenses
incurred by the Bank through the date hereof, including reasonable attorneys'
fees and expenses, and after the date hereof, all Bank Expenses, including
reasonable attorneys' fees and expenses, as and when they become due.

         5. CONDITIONS PRECEDENT TO FURTHER ADVANCES. The obligation of Bank to
make further advances to Borrower under this line is subject to the condition
precedent that Bank shall have received, in form and substance satisfactory to
Bank, the following:

                  (a)      this Second Loan Modification Agreement and the 
Equipment Line Promissory Note duly executed by Borrower;

                  (b) such other documents, and completion of such other
matters, as Bank may reasonably deem necessary or appropriate.

         6. CONSISTENT CHANGES. The Existing Loan Documents are hereby amended
wherever necessary to reflect the changes described in this Second Loan
Modification Agreement.

         7. NO DEFENSES OF BORROWER. Borrower agrees that as of this date, it
has no defenses against any of the obligations to pay any amounts under the
Indebtedness.

         8. CONTINUING VALIDITY. Borrower understands and agrees that (i) in
modifying the Existing Loan Documents, Bank is relying upon Borrower's
representations, warranties and agreements, as set forth in the Existing Loan
Documents, (ii) except as expressly modified pursuant to this Second Loan
Modification Agreement (including the effects of Section 6 hereof), the Existing
Loan Documents remain unchanged and in full force and effect, (iii) Bank's
agreement to modify the Existing Loan Documents pursuant to this Second Loan
Modification Agreement shall in no way obligate Bank to make any future
modifications to the Existing Loan Documents, (iv) it is the intention of Bank
and Borrower to retain as liable parties all makers and endorsers of the
Existing Loan Documents, unless a party is expressly released by Bank in
writing, (v) no maker, endorser or guarantor will be released by virtue of this
Second Loan Modification Agreement, and (vi) the terms of this Section 8 apply
not only to this Second Loan Modification Agreement but also to all subsequent
loan modification agreements, if any.

         9. EFFECTIVENESS. This Agreement shall become effective only when it
shall have been executed by Borrower and Bank (provided, however, in no event
shall this Agreement become effective until signed by an officer of Bank in
California).


                                       8

<PAGE>

         IN WITNESS WHEREOF, the parties hereto have caused this Agreement to be
executed as a sealed instrument as of the date first set forth above.


"Borrower": ENDOGEN, INC.            "Bank": SILICON VALLEY BANK, doing business
                                      as SILICON VALLEY EAST


By:                                   By: 
    ------------------------------        ------------------------------
    Owen A. Dempsey, President            Phillip S. Ernst, VP



                                      SILICON VALLEY BANK

                                      By: 
                                          -------------------------------

                                      Title: 
                                             ----------------------------
                                      (Signed in Santa Clara County, California)


                            EXHIBITS C AND D FOLLOWS



                                       9

<PAGE>


                                    EXHIBIT C

                           BORROWING BASE CERTIFICATE

<TABLE>
<S>               <C>                                                     <C>             <C>
Borrower:         Endogen, Inc.                                           Lender:         Silicon Valley Bank
                  30 Commerce Way                                                         3003 Tasman Drive
                  Woburn, MA 01801                                                        Santa Clara, CA 95054

Commitment Amount: $850,000

ACCOUNTS RECEIVABLE
         1.       Accounts Receivable Book Value as of ________________                                   $__________
         2.       Additions (please explain on reverse)                                                   $__________
         3.       TOTAL ACCOUNTS RECEIVABLE                                                               $__________

ACCOUNTS RECEIVABLE DEDUCTIONS
         4.       Amounts over 90 days due                                              $_________
         5.       Credit Balances Applied to Over 90-Day Accounts                       $_________
         6.       Balance of 50% over 90 day accounts                                   $_________
         7.       Concentration Limits                                                  $_________
         8.       Ineligible Foreign Accounts                                           $_________
         9.       Governmental Accounts                                                 $_________
         10.      Contra Accounts                                                       $_________
         11.      Promotion or Demo Accounts                                            $_________
         12.      Intercompany/Employee Accounts                                        $_________
         13.      Other (please explain on reverse)                                     $_________
         14.      TOTAL ACCOUNTS RECEIVABLE DEDUCTIONS                                                    $_________
         15.      Eligible Accounts (#3 - #14)                                                            $_________
         16.      LOAN VALUE OF ACCOUNTS (75% of #15)                                                     $_________


BALANCES
         17.      Maximum Loan Amount                                                                     $ 850,000
         18.      Total Funds Available (Lesser of #17 or #16)                                            $_________
         19.      Present balance owing on Line of Credit                                                 $_________
         20.      Outstanding under Sublimits (L/C - $250,000, FX - $250,000)                             $_________
         21.      RESERVE POSITIVE (#18 - #19 + #20)                                                      $_________

</TABLE>

The undersigned represents and warrants that the foregoing is true, complete and
correct, and that the information reflected in this Borrowing Base Certificate
complies with the representations and warranties set forth in the Loan and 
Security Agreement dated August 28, 1996, as may be amended from time to time,
between the undersigned and Silicon Valley Bank.



COMMENTS:

                                                      BANK USE ONLY

                                                      Rec'd By:
                                                                ----------------
                                                                Auth. Signer

                                                      Date:
                                                            --------------------

ENDOGEN, INC.                                         Verified:
                                                               -----------------
                                                               Auth. Signer

By:                                                   Date:
    --------------------                                    --------------------
       Authorized Signer



                                       10


<PAGE>


                                    EXHIBIT D
                             COMPLIANCE CERTIFICATE

Borrower:         Endogen, Inc.        Lender:         Silicon Valley Bank
                  30 Commerce Way                      3003 Tasman Drive
                  Woburn, MA 01801                     Santa Clara, CA 95054

         The undersigned authorized officer of ENDOGEN, INC. hereby certifies
that in accordance with the terms and conditions of the Loan and Security
Agreement dated AUGUST 28, 1996 between Borrower and Bank, as amended (the "Loan
Agreement"), (i) Borrower is in complete compliance for the period ending
___________ of all required conditions and terms except as noted below and (ii)
all representations and warranties of Borrower stated in the Agreement are true,
accurate and complete in all material respects as of the date hereof. Attached
herewith are the required documents supporting the above certification. The
Officer further certifies that these are prepared in accordance with Generally
Accepted Accounting Principals (GAAP) and are consistent from one period to the
next except as explained in an accompanying letter or footnotes.

  Please indicate compliance status by circling Yes/No under '"Complies" column

<TABLE>
<CAPTION>
                 Reporting Covenant                                   Required                           Complies
                 ------------------                                   --------                           --------
<S>                                                   <C>                                                 <C>         <C>
SEC Form 10Q                                          Within 5 days of SEC filing                         Yes         No
SEC Form 10K                                          Within 5 days of SEC filing                         Yes         No
A/R & A/P Agings                                      Monthly within 25 days                              Yes         No
A/R Audit                                             Annual                                              Yes         No

                Financial Covenants                        Required              Actual                  Complies
                -------------------                        --------              ------                  --------
Maintain on a Quarterly Basis:
------------------------------
Minimum Quick Ratio commencing 8/31/97                     1.10:1.0          __________:1.0              Yes         No
Maximum Debt/TNW                                           0.75:1.0          __________:1.0              Yes         No
Minimum TNW                                               $4,000,000        $__________                  Yes         No
Minimum Profitability *                                       $1            $__________                  Yes         No
Minimum Debt Service                                        1.5:1.0          __________:1.0              Yes         No

</TABLE>

*   Maximum loss of $75,000 allowed in any one quarter during the fiscal year 
    commencing 9/1/97.

Comments Regarding Exceptions:



On behalf of Borrower, the Officer further acknowledges that at any such time as
Borrower is out of compliance with any of the terms set forth in the Agreement,
including, without limitation, any of the financial covenants, Borrower cannot
receive any advances.

Sincerely,
                                                      BANK USE ONLY
--------------------------             Received by: 
Signature                                            ---------------------------
                                        Date: 
--------------------------                    ----------------------------------
TITLE                                   Verified: 
                                                  ------------------------------
--------------------------              Date: 
DATE                                          ----------------------------------

                                        Compliance Status:           Yes      No