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                                                                   EXHIBIT 10.13


                                 PREFERRED STOCK
                               PURCHASE AGREEMENT

                                     between


                              INTRACEL CORPORATION


                                       and


                        NORTHSTAR HIGH TOTAL RETURN FUND






                           Dated as of March 12, 1997



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                                                                                           Page
                                                                                      
               ARTICLE I THE SERIES A-2 PREFERRED.............................................1

SECTION 1.1.   Issuance, Sale and Delivery of the Series A-2 Preferred........................1

SECTION 1.2.   Closing Date...................................................................1


               ARTICLE II REPRESENTATIONS AND WARRANTIES OF THE COMPANY.......................1

SECTION 2.1.   Organization, Qualifications and Corporate Power...............................2

SECTION 2.2.   Authorization of Agreements, etc...............................................2

SECTION 2.3.   Validity.......................................................................3

SECTION 2.4.   Authorized Capital Stock.......................................................3

SECTION 2.5.   Financial Statements...........................................................4

SECTION 2.5A.  Absence of Undisclosed Liabilities and Changes.................................5

SECTION 2.6.   Events Subsequent to the Date of the Balance Sheet.............................5

SECTION 2.7.   Litigation; Compliance with Law................................................5

SECTION 2.8.   Title to Properties............................................................6

SECTION 2.9.   Leasehold Interests............................................................6

SECTION 2.10.  Insurance......................................................................6

SECTION 2.11.  Taxes..........................................................................7

SECTION 2.12.  Other Agreements...............................................................7

SECTION 2.13.  Patents, Trademarks, etc.......................................................8

SECTION 2.14.  Loans and Advances.............................................................9

SECTION 2.15.  Assumptions, Guaranties, etc. of Indebtedness of Other Persons.................9

SECTION 2.16.  Significant Customers and Suppliers............................................9

SECTION 2.17.  Governmental Approvals.........................................................9

SECTION 2.18.  Accuracy of Statements........................................................10


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SECTION 2.19. Employment Relations..........................................................10

SECTION 2.20. Compensation of Key Employees.................................................10

SECTION 2.21. Environmental Compliance......................................................10

              ARTICLE III REPRESENTATIONS AND WARRANTIES OF THE PURCHASER...................10

SECTION 3.1.  Purchase of Series A-I Preferred..............................................10

SECTION 3.2.  Authority.....................................................................11

SECTION 3.3.  Projections...................................................................11


              ARTICLE IV CONDITIONS TO THE OBLIGATIONS OF THE PURCHASER.....................11

SECTION 4.1.  Opinion of Company's Counsel..................................................12

SECTION 4.2.  Representations and Warranties to be True and Correct.........................12

SECTION 4.3.  Performance...................................................................12

SECTION 4.4.  All Proceedings to be Satisfactory............................................12

SECTION 4.5.  Supporting Documents..........................................................12

SECTION 4.6.  Legal Fees....................................................................13

SECTION 4.7.  Certificate of Designation....................................................13

SECTION 4.8.  Consents......................................................................13


              ARTICLE V COVENANTS OF THE COMPANY............................................13

SECTION 5.1.  Financial Statements, Reports, etc............................................13

SECTION 5.2.  Corporate Existence...........................................................15

SECTION 5.3.  Properties, Business, Insurance...............................................15

SECTION 5.4.  Inspection, Consultation and Advice...........................................15

SECTION 5.5.  Restrictive Agreements Prohibited.............................................15

SECTION 5.6.  Board of Directors Meetings...................................................16

SECTION 5.7.  Compliance with Laws..........................................................16

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SECTION 5.8.  Keeping of Records and Books of Account.......................................16

SECTION 5.9.  Maintaining Nature of Business................................................16

SECTION 5.10. Obligations and Taxes.........................................................16

SECTION 5.11. Further Issuances of Series A-I Preferred.....................................16

SECTION 5.12.  Notices......................................................................16

SECTION 5.13. Environmental Matters.........................................................17

SECTION 5.14. The Exchange Notes; Security Interest; Guaranty...............................18

SECTION 5.15. Waivers.......................................................................18

SECTION 5.17. Further Assurances............................................................19


              ARTICLE VI MISCELLANEOUS......................................................19

SECTION 6.1.  Expenses......................................................................19

SECTION 6.2.  Survival of Agreements........................................................19

SECTION 6.3.  Brokerage.....................................................................19

SECTION 6.4.  Parties in Interest...........................................................20

SECTION 6.5.  Notices; Payment of Dividends.................................................20

SECTION 6.6.  Replacement of Certificates...................................................20

SECTION 6.7.  Governing Law.................................................................21

SECTION 6.8.  Entire Agreement..............................................................21

SECTION 6.9.  Submission to Jurisdiction; Waivers...........................................21

SECTION 6.10. Counterparts..................................................................21

SECTION 6.11. Amendments....................................................................22

SECTION 6.12. Severability..................................................................22

SECTION 6.13. Titles and Subtitles..........................................................22


              SCHEDULE I....................................................................24

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PREFERRED STOCK PURCHASE AGREEMENT, dated as of March 12, 1997 between Intracel
Corporation, a Massachusetts corporation (the "Company") and Northstar High
Total Return Fund (the "Purchaser").

        WHEREAS, the Company wishes to issue and sell to the Purchaser an
aggregate of 40,000 shares (the "Shares") of the Company's Series A-2 Preferred
Stock, no par value (the "Series A-2 Preferred"), of which 155,000 shares are
authorized, for an aggregate purchase price of $4,000,000, which shares shall be
issued to the Purchaser in the amount and for the consideration set forth across
from the Purchaser's name as set forth on Schedule I hereto; and

        WHEREAS, the Purchaser wishes to purchase the Series A-2 Preferred on
the terms and subject to the conditions set forth in this Agreement.

        NOW, THEREFORE, in consideration of the premises and the mutual
covenants contained in this Agreement, the parties hereto agree as follows:


                                    ARTICLE I

                            THE SERIES A-2 PREFERRED

        SECTION 1.1. Issuance, Sale and Delivery of the Series A-2 Preferred.
The Company agrees to issue and sell to the Purchaser, and the Purchaser hereby
agrees to purchase from the Company, the Shares.

        SECTION 1.2. Closing Date. The closing of the sale and purchase of the
Shares (the "Closing"), will take place at the offices of Morrison & Foerster
LLP, 1290 Avenue of the Americas, New York, NY 10104, at 10:00 a.m., New York
time, as of the date hereof, or at such other place, time and date as may be
otherwise mutually agreed in writing by the parties hereto. The date on which
the Closing occurs is referred to herein as the "Closing Date". At the Closing,
the Company shall issue and deliver to the Purchaser a stock certificate or
certificates in definitive form, registered in the name of the Purchaser,
representing the Series A-2 Preferred being purchased by it at the Closing, as
indicated on Schedule I hereto. The parties hereto agree that the Shares as are
to be purchased by the Purchaser shall be delivered to the Purchaser's
designated custodian for delivery to the Purchaser's funding agent which shall,
upon receipt of such certificate, release for delivery the Notes (as hereinafter
defined) to be delivered by Purchaser pursuant to Schedule I hereto and wire
transfer immediately available funds in the amount of the cash consideration to
be paid by the Purchaser in accordance with Schedule I for such Shares to the
account of the Company previously designated by it.


                                   ARTICLE II

                  REPRESENTATIONS AND WARRANTIES OF THE COMPANY

        The Company represents and warrants to the Purchaser as of the Closing
Date that:
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        SECTION 2.1. Organization, Qualifications and Corporate Power. The
Company is a corporation duly organized (originally under the name of Boston
Biological Technologies, Inc.), validly existing and in good standing under the
laws of the Commonwealth of Massachusetts; Bartels, Inc. (the Company's wholly
owned subsidiary)("Bartels") is a corporation duly organized, validly existing
and in good standing under the laws of the State of Delaware; and each of the
Company and Bartels is duly licensed or qualified to transact business as a
foreign corporation and is in good standing in each jurisdiction in which the
nature of the business transacted by it or the character of the properties owned
or leased by it requires such licensing or qualification, except where the
failure so to qualify will not have a material adverse effect on the business,
operations, property or financial condition of the Company or Bartels,
respectively. Each of the Company and Bartels has the power and authority to own
and hold its properties and to carry on its business as now conducted and as
proposed to be conducted, to execute, deliver and perform this Agreement, and to
issue, sell and deliver the Series A-2 Preferred. The Company has no direct or
indirect subsidiaries, other than Bartels and the Company's ownership of
forty-five percent of the membership interests of the German-American Institute
for AIDS Research GmbH, a limited liability company formed under the laws of
Germany.

        SECTION 2.2. Authorization of Agreements, etc. (a) The execution and
delivery by the Company of this Agreement, the performance by the Company of its
obligations hereunder and the issuance, sale and delivery of the Series A-2
Preferred have been duly authorized by all requisite corporate action and will
not violate any provision of law, any order of any court or other agency of
government, the Articles of Organization of the Company, as amended (the
"Charter") or the By-laws of the Company, as amended, or any provision of any
indenture, agreement or other instrument to which either the Company or Bartels
is a party or by which either the Company or Bartels or any of its properties or
assets is bound, or conflict with, result in a breach of or constitute (whether
with or without notice or lapse of time or both) a default under any such
indenture, agreement or other instrument, or result in the creation or
imposition of any lien, charge, restriction, claim or encumbrance of any nature
whatsoever upon any of the properties or assets of the Company or Bartels other
than the Company's loan agreement with the Massachusetts Business Development
Corporation ("MBDC"), consent from which the Purchaser hereby expressly waives;
provided, however, that the Company shall either obtain the consent of MBDC to
the transactions contemplated by this Agreement by the date which is 60 days
after the Closing Date or, in the event the Company fails to obtain such consent
by such date, pay all amounts due under such loan agreement.

               (b) The Series A-2 Preferred has been duly authorized and, when
        issued in accordance with this Agreement, will be validly issued, fully
        paid and nonassessable with no personal liability attaching to the
        ownership thereof and will be free and clear of all liens, charges,
        restrictions, claims and encumbrances imposed by or through the Company.
        The issuance, sale or delivery of the Series A-2 Preferred is not
        subject to any preemptive right of stockholders of the Company or to any
        right of first refusal or other right in favor of any person.

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               (c) Except as set forth in Schedule 2.2(c), there is no party
        without whose consent the Company could not pay dividends in cash to the
        Purchaser as provided under the terms of the Series A-2 Preferred.

        SECTION 2.3. Validity. This Agreement has been duly executed and
delivered by the Company and constitutes the legal, valid and binding obligation
of the Company, enforceable in accordance with its terms, subject to (i)
applicable bankruptcy, insolvency, reorganization, fraudulent conveyance and
moratorium laws and other similar laws of general application affecting
enforcement of creditors' rights generally and (ii) the availability of
equitable remedies, including specific performance, which may be limited by
equitable principles of general applicability (regardless of whether enforcement
is sought in a proceeding in equity or at law).

        SECTION 2.4. Authorized Capital Stock. The authorized capital stock of
(a) the Company consists of (i) 3,000,000 shares of Preferred Stock, no par
value per share (the "Preferred Stock"), of which 730,000 shares have been
designated Series A Preferred and 850,000 shares which have been designated
Series A-1 Preferred and 155,000 shares will have been designated Series A-2
Preferred in connection with this Closing and (ii) 5,000,000 shares of common
stock, no par value per share (the "Common Stock") and (b) Bartels consists of
1,000 shares of common stock, par value $.01 per share. Immediately prior to the
Closing, all of the capital stock of Bartels which is issued and outstanding
will be owned by the Company, 1,983,593 shares of Common Stock will be
outstanding, all of which will be validly issued and outstanding, fully paid and
nonassessable with no personal liability attaching to the ownership thereof,
557,653 shares of Series A Preferred will be outstanding pursuant to the
Convertible Stock Purchase Agreement, dated July 22, 1994, by and among the
Company and the Purchasers set forth on Schedule I thereto (the "1994 Stock
Purchase Agreement") and 601,569 shares of Series A-1 Preferred will be
outstanding pursuant to the Convertible Stock Purchase Agreement, dated as of
September 22, 1995 by and among the Company and the Purchasers set forth on
Schedule I thereto (the "1995 Stock Purchase Agreement") and 136,658 shares of
Series A-1 Preferred will be issued and outstanding pursuant to a Convertible
Preferred Stock Purchase Agreement dated November 16, 1995, between the Company
and Creditanstalt American Corporation and 40,000 shares of Series A-2 Preferred
will be issued on even date herewith pursuant to this Agreement. No other shares
of capital stock of the Company or Bartels have been issued or reserved for
issuance, except 385,000 shares of Common Stock reserved for issuance in the
event options granted pursuant to the 1989 and 1990-1991 Stock Option Plans of
the Company are exercised, 730,000 shares of Common Stock reserved for issuance
in the event of the conversion of the shares of Series A Preferred Stock and
52,000 shares of Common Stock reserved for issuance in the event of the exercise
of the Series A Warrant, both having been granted pursuant to the 1994 Stock
Purchase Agreement, 850,000 shares of Common Stock reserved for issuance in the
event of the conversion of the shares of Series A-I Preferred Stock granted
pursuant to the 1995 Stock Purchase Agreement, 86,462 shares of Common Stock
reserved for issuance in the event of the exercise of warrants granted pursuant
to the Warrant Agreement, dated September 22, 1995, between the Company and
Dublind Investments, L.L.C., 91,177 shares of Common Stock reserved for issuance
in the event of the exercise of the warrants granted pursuant to the Warrant
Agreement, dated November 16, 1995, between the Company and Creditanstalt
Bankverein ("Creditanstalt"), 94,010 shares of Common Stock reserved for


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issuance in the event of exercise of the warrants granted pursuant to the Series
A-II Warrant and Note Purchase Agreement, dated December 27, 1995, between the
Company and Purchaser, 159,073 shares of Common Stock reserved for issuance in
the event of exercise of the warrants granted pursuant to the Note and Series
A-III Warrant Purchase Agreement, dated June 11, 1996 between the Company and
CoreStates Enterprise Fund, a division of CoreStates Bank, N.A. ("CoreStates")
and 79,537 shares of Common Stock reserved for issuance in the event of the
exercise of the Warrant granted pursuant to the Note and Series A-IV Warrant
Purchase Agreement, dated June 21, 1996 between the Company and Purchaser (the
"Note Agreement"). The designations, powers, preferences, rights,
qualifications, limitations and restrictions in respect of the Series A
Preferred Stock, the Series A-1 Preferred Stock and the Series A-2 Preferred
Stock are as set forth in both of the Certificates of Vote of Directors
Establishing a Series of a Class of Stock, and all such designations, powers,
preferences, rights, qualifications, limitations and restrictions are valid,
binding and enforceable and in accordance with all applicable laws. Except as
provided for in the Charter, the Company has no obligation (contingent or other)
to purchase, redeem or otherwise acquire any of its equity securities or any
interest therein or to pay any dividend or make any other distribution in
respect thereof. This Section 2.4 sets forth the aggregate number of outstanding
warrants, options, agreements, convertible securities or other commitments
pursuant to which the Company is or may become obligated to issue any shares of
its capital stock or other securities of the Company. Except as set forth above
in this Section 2.4, there are no preemptive or similar rights to purchase or
otherwise acquire shares of capital stock of the Company pursuant to any
provisions of law, the Charter or By-laws of the Company, in each case as
amended to the date hereof, or any agreement to which the Company is a party or
otherwise. Except as set forth above in this Section 2.4, or as contemplated
herein, immediately upon consummation at the Closing of the transactions
contemplated hereby there will be no agreement, restriction or encumbrance (such
as a right of first refusal, right of first offer, proxy, voting agreement,
voting trust, bring-along or come-along rights) with respect to the sale or
voting of any shares of capital stock of the Company (whether outstanding or
issuable upon conversion or exercise of outstanding securities) of which the
Company has knowledge.

        SECTION 2.5. Financial Statements. The Company has furnished to the
Purchaser the audited balance sheet of the Company for the six months ended
December 31, 1995 (the "Balance Sheet") and the related audited statements of
income, stockholders' equity and cash flows of the Company for the six months
ended December 31, 1995, and the balance sheet of the Company as of September
30, 1996 and the related statements of income, stockholders' equity and cash
flows of the Company as of September 30, 1996. All such financial statements
have been prepared in accordance with generally accepted accounting principles
consistently applied and fairly present the financial position of the Company as
of December 31, 1995 and September 30, 1996, respectively, and the results of
its operations and cash flows as of December 31, 1995 and September 30, 1996,
respectively. Except as set forth on Schedule 2.12, since the date of the
Balance Sheet, (i) there has been no change in the assets, liabilities or
financial condition of the Company from that reflected in the Balance Sheet
except for changes in the ordinary course of business which in the aggregate
have not been materially adverse and (ii) none of the business, financial
condition, operations or property of the Company have been materially adversely


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affected by any occurrence or development, individually or in the aggregate,
whether or not insured against.

        SECTION 2.5A. Absence of Undisclosed Liabilities and Changes. Except as
set forth on Schedule 2.5A attached hereto, as of the date hereof, (a) the
Company had no liabilities of any nature (matured or unmatured, fixed or
contingent) which were not provided for on the balance sheet of the Company as
of such date, except for (i) liabilities which, individually and in the
aggregate, were not material to the financial condition of the Company or (ii)
liabilities incurred in the ordinary course of the Company's business and not
required to be so provided for under generally accepted accounting principles,
and (b) all reserves established by the Company and set forth on such balance
sheet were adequate in all material respects. There are no loss contingencies
(as such term is used in Statement of Financial Accounting Standards No. 5
("Statement No. 5") issued by the Financial Accounting Standards Board in March
1975) which are not adequately provided for in such balance sheet as required by
Statement No. 5.

        SECTION 2.6. Events Subsequent to the Date of the Balance Sheet. Except
as set forth in the attached Schedule 2.6, since the date of the Balance Sheet,
except as contemplated by this Agreement, neither the Company nor Bartels has
(i) issued any stock, bond or other corporate security, (ii) borrowed any amount
or incurred or become subject to any liability (absolute, accrued or
contingent), except current liabilities incurred and liabilities under contracts
entered into in the ordinary course of business, (iii) discharged or satisfied
any lien or encumbrance or incurred or paid any obligation or liability
(absolute, accrued or contingent) other than current liabilities shown on the
Balance Sheet and current liabilities incurred since the date of the Balance
Sheet in the ordinary course of business, (iv) declared or made any payment or
distribution to stockholders or purchased or redeemed any share of its capital
stock or other security, (v) mortgaged, pledged or subjected to lien any of its
assets, tangible or intangible, other than liens of current real property taxes
not yet due and payable, (vi) sold, assigned or transferred any of its tangible
assets except in the ordinary course of business, or canceled any debt or claim,
(vii) sold, assigned, transferred or granted any exclusive license with respect
to any material patent, trademark, trade name, service mark, copyright, trade
secret or other intangible asset other than in the ordinary course of business,
(viii) suffered any material loss of property or waived any right of substantial
value, (ix) made any change in officer compensation except in the ordinary
course of business and consistent with past practice, (x) made any material
change in the manner of business or operations of the Company or Bartels,
respectively, (xi) entered into any transaction except in the ordinary course of
business or as otherwise contemplated hereby or (xii) entered into any
commitment (contingent or otherwise) to do any of the foregoing.

        SECTION 2.7. Litigation; Compliance with Law. Except as set forth in the
attached Schedule 2.6, there is no material (i) action, suit, claim, proceeding
or investigation pending or, to the knowledge of the Company, threatened against
or affecting the Company or Bartels, respectively, at law or in equity, or
before or by any Federal, state, municipal or other governmental department,
commission, board, bureau, agency or instrumentality, domestic or foreign, (ii)
arbitration proceeding relating to the Company or Bartels, respectively, pending
under a collective bargaining agreement or otherwise or (iii) governmental
inquiry pending or, to 


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the knowledge of the Company, threatened against or affecting the Company or
Bartels, respectively (including, without limitation, any inquiry as to the
qualification of the Company or Bartels, respectively, to hold or receive any
license or permit). The Company has not received any opinion or memorandum or
legal advice from legal counsel to the effect that it is exposed, from a legal
standpoint, to any liability or disadvantage which may be material to its
business, financial condition, operations or property. The Company is not in
default with respect to any order, writ, injunction or decree known to or served
upon the Company of any court or of any Federal, state, municipal or other
governmental department, commission, board, bureau, agency or instrumentality,
domestic or foreign. There is no material action or suit by the Company pending
or threatened against others. Each of the Company and Bartels has complied in
all material respects with all laws, rules, regulations and orders applicable to
its business, operations, properties, assets, products and services, and each of
the Company and Bartels has all necessary permits, licenses and other
authorizations required to conduct its business as conducted and as proposed to
be conducted, except where the failure to own or possess such permits, licenses
or authorizations could not, either singly or in the aggregate, have a material
adverse effect on the business, operations, properties or financial condition of
the Company.

        SECTION 2.8. Title to Properties. Except in instances that, either
singly or in the aggregate, could not have a material adverse effect on the
business, operations, properties or financial condition of the Company, and
except as disclosed in Schedule 2.8 hereof, each of the Company and Bartels has
good and marketable title to its properties and assets reflected on the Balance
Sheet (other than properties and assets disposed of in the ordinary course of
business since the date of the Balance Sheet), and all such properties and
assets are free and clear of mortgages, pledges, security interests, liens,
charges, claims, restrictions and other encumbrances, except for liens for
current taxes not yet due and payable and minor imperfections of title, if any,
not material in nature or amount and not materially detracting from the value or
materially impairing the use of the property subject thereto or impairing the
operations or proposed operations of the Company or Bartels, respectively.

        SECTION 2.9. Leasehold Interests. Each lease or agreement to which the
Company or Bartels, respectively, is a party under which it is a lessee of any
property, real or personal (a list of all leases being attached hereto as
Schedule 2.9), is a valid and subsisting agreement without any material default
of the Company or Bartels, respectively, thereunder and, to the knowledge of the
Company, without any material default thereunder of any other party thereto. No
event has occurred and is continuing which, with due notice or lapse of time or
both, would constitute a default or event of default by the Company or Bartels,
respectively, under any such lease or agreement or, to the knowledge of the
Company, by any other party thereto.

        SECTION 2.10. Insurance. The Company holds valid policies covering all
of the insurance required to be maintained by it under Section 5.3. Schedule
2.10 lists all insurance policies which the Company maintains with respect to
its businesses, properties and employees. Such policies are in full force and
effect and the Company has received no notice of termination from the insurance
carriers. Such policies, with respect to their amounts, deductibles and types of
coverage, are adequate in the reasonable commercial judgment of the Company to
insure against risks to which the Company and its respective businesses are
subject. Since the date of 



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the Balance Sheet, there has been no material adverse change in the Company's
relationship with its insurers or in the premiums payable pursuant to such
policies.

        SECTION 2.11. Taxes. The Company has filed or will file within the time
prescribed by law (including extensions of time approved by the appropriate
taxing authority) all tax returns, foreign, Federal, state, county and local,
required to be filed by it, and the Company has paid all taxes shown to be due
by such returns and extensions as well as all other taxes, assessments and
governmental charges which have become due or payable, including, without
limitation, all taxes which the Company is obligated to withhold from amounts
owing to employees, creditors and third parties. All such taxes with respect to
which the Company has become obligated have been paid and adequate reserves have
been established for all taxes accrued but not yet payable. No deficiency
assessment with respect to or proposed adjustment of the Company's foreign,
Federal, state, county or local taxes is pending or, to the knowledge of the
Company, threatened. There is no tax lien in favor of any foreign, Federal,
state, county or local authority, outstanding against the assets, properties or
business of the Company. Neither the Company nor any of its stockholders has
ever filed a consent pursuant to Section 341(f) of the internal Revenue Code of
1986, as amended (the "Code"), relating to collapsible corporations.

        SECTION 2.12. Other Agreements. Except as set forth in the attached
Schedule 2.12, neither the Company nor Bartels is a party to or otherwise bound
by any written or oral contract or instrument or other restriction which
individually or in the aggregate could materially adversely affect the business,
financial condition, operations or property of the Company. Except as set forth
in the attached Schedule 2.12, or as a result of the transactions contemplated
in this Agreement, neither the Company nor Bartels is a party to or otherwise
bound by any written or oral:

               (a) distributor, dealer, manufacturer's representative or sales
        agency contract or agreement which is not terminable on less than ninety
        (90) days' notice without cost or other liability to the Company;

               (b) sales contract which entitles any customer to a rebate or
        right of set-off, to return any product to the Company after acceptance
        thereof or to delay the acceptance thereof, or which varies in any
        material respect from the Company's standard form contracts;

               (c) contract with any labor union (and, to the knowledge of the
        Company, no organizational effort is being made with respect to any of
        its employees);

               (d) contract or other commitment with any supplier containing any
        provision permitting any party other than the Company or Bartels to
        renegotiate the price or other terms, or containing any pay-back or
        other similar provision, upon the occurrence of a failure by the Company
        or Bartels to meet its obligations under the contract when due or the
        occurrence of any other event;

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               (e) contract for the future purchase of fixed assets or for the
        future purchase of materials, supplies or equipment in excess of its
        normal operating requirements;

               (f) contract for the employment of any officer, employee or other
        person (whether of a legally binding nature or in the nature of informal
        understandings) on a full-time or consulting basis which is not
        terminable on notice without cost or other liability to the Company,
        except normal severance arrangements and accrued vacation pay;

               (g) agreement or indenture relating to the borrowing of money or
        to the mortgaging or pledging of, or otherwise placing a lien or
        security interest on, any asset of the Company or Bartels;

               (h) guaranty of any obligation for borrowed money or otherwise;

               (i) agreement, or group of related agreements with the same party
        or any group of affiliated parties, under which the Company or Bartels
        has advanced or agreed to advance money or has agreed to lease any
        property as lessee or lessor;

               (j) agreement or obligation (contingent or otherwise) to issue,
        sell or otherwise distribute or to repurchase or otherwise acquire or
        redeem any share of its capital stock or any of its other equity
        securities;

               (k) assignment, license or other agreement with respect to any
        form of intangible property or Intellectual Property or the development
        or use thereof;

               (l) agreement under which it has granted any person any 
        registration rights;

               (m) agreement under which it has limited or restricted its right
        to compete with any person in any respect; or

               (n) other contract or group of related contracts with the same
        party involving more than $50,000 or continuing over a period of more
        than one year from the date or dates thereof (including renewals or
        extensions optional with another party), which contract or group of
        contracts is not terminable by the Company or Bartels without penalty
        upon notice of thirty (30) days or less, but excluding any contract or
        group of contracts with a customer of the Company or Bartels for the
        sale, lease or rental of the Company's or Bartels' products or services
        if such contract or group of contracts was entered into by the Company
        or Bartels in the ordinary course of business.

        SECTION 2.13. Patents, Trademarks, etc. Set forth in Schedule 2.13 is a
list and brief description of all patents, patent rights, patent applications,
trademarks, trademark applications, service marks, service mark applications,
trade names and copyrights, and all applications for such which are in the
process of being prepared, owned by or registered in the name of the Company or
Bartels, or of which the Company or Bartels is a licensor or licensee or in
which the Company or Bartels has any right, and in each case a brief description
of the nature of such right. Except as set forth on Schedule 2.13, each of the
Company and Bartels owns or 




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possesses adequate licenses or other rights to use all patents, patent
applications, trademarks, trademark applications, service marks, service mark
applications, trade names, copyrights, manufacturing processes, formulas, trade
secrets and know-how (collectively, "Intellectual Property") necessary to the
conduct of its business as presently conducted, and no claim is pending or, to
the knowledge of the Company, threatened to the effect that the operations of
the Company or Bartels infringe upon or conflict with the rights of any other
person under any Intellectual Property, and to the knowledge of the Company
there is no basis for any such claim. No claim is pending or to the knowledge of
the Company threatened to the effect that any such Intellectual Property owned
or licensed by the Company or Bartels, or which the Company or Bartels otherwise
has the right to use, is invalid or unenforceable by the Company, and to the
knowledge of the Company there is no basis for any such claim. To the knowledge
of the Company, all technical information developed by and belonging to the
Company or Bartels, as applicable, which has not been patented, has been kept
confidential. The Company has not granted or assigned to any other person or
entity any right to manufacture, have manufactured, assemble or sell any
products or proposed products of the Company and to the knowledge of the Company
no other person or entity has asserted any such right.

        SECTION 2.14. Loans and Advances. Except as set forth on Schedule 2.14,
neither the Company nor Bartels has any outstanding loans or advances to any
person and is not obligated to make any such loans or advances, except, in each
case, for advances to employees of the Company or Bartels in respect of
reimbursable business expenses anticipated to be incurred by them in connection
with their performance of services for the Company or Bartels.

        SECTION 2.15. Assumptions, Guaranties, etc. of Indebtedness of Other
Persons. Neither the Company nor Bartels has assumed, guaranteed, endorsed or
otherwise become directly or contingently liable on any indebtedness of any
other person (including, without limitation, liability by way of agreement,
contingent or otherwise, to purchase, to provide funds for payment, to supply
funds to or otherwise invest in a debtor, or otherwise to assure a creditor
against loss), except for guaranties by endorsement of negotiable instruments
for deposit or collection in the ordinary course of business.

        SECTION 2.16. Significant Customers and Suppliers. No customer which
accounted for 10% or more of the Company's sales or revenues during the periods
covered by the financial statements referred to in Section 2.5 or which has been
significant to the Company thereafter has terminated, materially reduced or
threatened to terminate or materially reduce its purchases from the Company. As
of the date of this Agreement, there is no supplier to the Company which is a
sole-source supplier.

        SECTION 2.17. Governmental Approvals. Subject to the accuracy of the
representations and warranties of the Purchaser set forth in Article III, no
registration or filing with, or consent or approval of or other action by, any
Federal, state or other governmental agency or instrumentality is or will be
necessary for the valid execution, delivery and performance by the Company of
this Agreement and the issuance, sale and delivery of the Series A-2 Preferred,
other than filings pursuant to state securities laws in connection with the sale
of the Series A-2 Preferred.



                                       9
   14

        SECTION 2.18. Accuracy of Statements. Neither this Agreement nor any
Schedule, Exhibit, statement, list, document, certificate or other information
furnished by or on behalf of the Company to the Purchaser in connection with
this Agreement or any of the transactions contemplated hereby contains any
untrue statement of a material fact or omits to state a material fact necessary
to make the statements contained herein or therein, in light of the
circumstances in which they are made, not misleading.

         SECTION 2.19. Employment Relations. (a) The Company is in material
compliance with applicable federal, state or other applicable laws, domestic or
foreign, respecting employment and employment practices, safety, terms and
conditions of employment and wages and hours.

               (b) The Company does not maintain or contribute to any employee
        benefit plan ("Employee Benefit Plan") within the meaning of Section
        3(3) of the Employee Retirement Income Security Act of 1974, as amended
        ("ERISA"), which is subject to ERISA but which is not in substantial
        compliance with ERISA, or which has incurred any material liability to
        the Pension Benefit Guaranty Company ("PBGC") in connection with any
        Employee Benefit Plan covering any employees of the Company or any of
        its subsidiaries or ceased operations at any facility or withdrawn from
        any such Plan in a manner which could subject it to material liability
        under Section 462(f), 4063 or 4064 of ERISA, and knows of no facts or
        circumstances which might give rise to any material liability of the
        Company to the PBGC under Title IV of ERISA.

        SECTION 2.20. Compensation of Key Employees. Schedule 2.20 sets forth
the aggregate compensation (salaries, wages and bonuses) paid by the Company to
its four most highly compensated employees for the 1996 fiscal year and the
amount of such compensation scheduled to be paid to such employees for the 1997
fiscal year.

        SECTION 2.21. Environmental Compliance. The Company is in compliance
with all applicable laws relating to environmental matters in each jurisdiction
where it is presently engaged in a material manufacturing business, except for
such failures to comply which, in the aggregate, could reasonably be expected
not to have a material adverse effect on the Company. The Company is not subject
to any liability under any such environmental laws, that, in the aggregate for
all such liabilities, could be reasonably expected to have a material adverse
effect on the Company.


                                   ARTICLE III

                       REPRESENTATIONS AND WARRANTIES OF THE PURCHASER

        The Purchaser represents and warrants to the Company as of the Closing
Date that:

         SECTION 3.1. Purchase of Series A-2 Preferred. (a) It is an "accredited
investor" within the meaning of Rule 501 under the Securities Act and was not
organized for the specific purpose of acquiring the Series A-2 Preferred.


                                       10
   15


               (b)    It has sufficient knowledge and experience in investing 
        in companies in a similar stage of development to the Company so as to
        be able to evaluate the risks and merits of its investment in the
        Company and it is able financially to bear the risks thereof.

               (c) It has had an opportunity to discuss the Company's business,
        management and financial condition with the Company's management.

               (d) It is purchasing the Series A-2 Preferred for its own account
        for the purpose of investment and not with a view to or for sale in
        connection with any distribution thereof.

               (e) It understands that (i) the Series A-2 Preferred has not been
        registered under the Securities Act by reason of their issuance in a
        transaction exempt from the registration requirements of the Securities
        Act pursuant to Section 4(2) thereof or Rule 505 or 506 promulgated
        under the Securities Act, (ii) the Series A-2 Preferred must be held
        indefinitely unless a subsequent disposition thereof is registered under
        the Securities Act or is exempt from such registration requirements,
        (iii) the Series A-2 Preferred will bear a legend to such effect and
        (iv) the Company will make a notation on its transfer ledger to such
        effect.

        SECTION 3.2. Authority. It has all requisite power and authority to
execute, deliver and perform this Agreement, and has taken all necessary action
to authorize the execution, delivery and performance of this Agreement and the
consummation of the transactions contemplated hereby. This Agreement on the
Closing Date will constitute, the legal, valid and binding obligation of the
Purchaser, enforceable in accordance with its terms, except (i) to the extent
that enforceability may be limited by bankruptcy, insolvency, moratorium,
fraudulent conveyance, reorganization or other similar laws affecting the
enforcement of creditors' rights generally and (ii) that the availability of
equitable remedies, including specific performance, is subject to the discretion
of the court before which any proceedings therefor may be brought.

        SECTION 3.3. Projections. It understands that any and all financial
projections and other estimates delivered to it were based on the Company's
experience in the industry and on assumptions of fact and opinion which the
Company believes to have been, and to be, reasonable. It understands that the
Company cannot and does not assure or guarantee the attainment of such
projections or other estimates.


                                   ARTICLE IV

                 CONDITIONS TO THE OBLIGATIONS OF THE PURCHASER

        The obligation of the Purchaser to purchase and pay for the Series A-2
Preferred being purchased by it on the Closing Date is, at its option, subject
to the satisfaction of the Purchaser and its counsel, on or before the Closing
Date, of the following conditions:



                                       11
   16

        SECTION 4.1. Opinion of Company's Counsel. The Purchaser shall have
received from Morrison & Foerster LLP, counsel for the Company, an opinion dated
the Closing Date, in the form attached as Exhibit B and otherwise satisfactory
in form and scope to the Purchaser and its counsel as to such other matters as
the Purchaser or its counsel may reasonably request.

        SECTION 4.2. Representations and Warranties to be True and Correct. The
representations and warranties contained in Article II shall be true, complete
and correct on and as of such Closing Date with the same effect as though such
representations and warranties had been made on and as of such date, and the
President of the Company shall have certified to such effect to the Purchaser in
writing.

        SECTION 4.3. Performance. The Company shall have performed and complied
with all agreements contained herein required to be performed or complied with
by it prior to or at the Closing Date, and the President of the Company shall
have certified to the Purchaser in writing to such effect and to the further
effect that all of the conditions set forth in this Article IV have been
satisfied.

        SECTION 4.4. All Proceedings to be Satisfactory. All corporate and other
proceedings to be taken by the Company in connection with the transactions
contemplated hereby and all documents incident thereto shall be satisfactory in
form and substance to the Purchaser and its counsel, and the Purchaser and its
counsel shall have received all such counterpart originals or certified or other
copies of such documents as they may reasonably request.

        SECTION 4.5. Supporting Documents. At the Closing, the Purchaser and
its counsel shall have received copies of the following documents:

               (a) (i) the Charter, certified as of a recent date by the
        Secretary of State of the Commonwealth of Massachusetts and (ii) a
        certificate of said Secretary dated as of a recent date as to the due
        incorporation and subsistence of the Company and listing all documents
        of the Company on file with said Secretary;

               (b) a certificate of the Clerk or an Assistant Clerk of the
        Company dated the Closing Date and certifying: (i) that attached thereto
        is a true and complete copy of the By-laws of the Company as in effect
        on the date of such certification; (ii) that attached thereto is a true
        and complete copy of all resolutions adopted by the Board of Directors
        of the Company authorizing the execution, delivery and performance of
        this Agreement, the issuance, sale and delivery of the Series A-2
        Preferred and that all such resolutions are in full force and effect and
        are all the resolutions adopted in connection with the transactions
        contemplated by this Agreement; (iii) that the Charter has not been
        amended since the date of the last amendment referred to in the
        certificate delivered pursuant to clause (a)(ii) above, except as
        contemplated by Exhibit A; and (iv) to the incumbency and specimen
        signature of each officer of the Company executing this Agreement or any
        of the stock certificates representing the Series A-2 Preferred and any
        certificate or instrument furnished pursuant hereto, and a certification
        by another officer of the Company as to the 



                                       12
   17

        incumbency and signature of the officer signing the certificate referred
        to in this clause (b); and

               (c) such additional supporting documents and other information
        with respect to the operations of the Company as the Purchaser or its
        counsel may reasonably request.

               (d) Legal Fees. At the Closing, the Company shall pay the
        reasonable fees and expenses of Reboul, MacMurray, Hewitt, Maynard &
        Kristol incurred for Northstar in connection with the transactions
        contemplated by this Agreement.

        SECTION 4.6. Certificate of Designation. The Certificate of Vote of
Directors Establishing a Series or a Class of Stock with respect to the Series
A-2 Preferred in substantially the form of Exhibit A (the "Certificate of
Designation") shall have been filed with the Secretary of State of
Massachusetts.

        SECTION 4.7. Consents. Except with respect to the consent of MBDC, the
obtaining of which consent the Purchaser has expressly waived, the written
consent of Creditanstalt Bankverein and any other party without whose consent
the Company could not effect the transactions contemplated hereby or pay cash
dividends to the Purchaser in respect of the Shares as provided for in the
Certificate of Designation shall have been received in form and substance
satisfactory to the Purchaser and its counsel.

                                    ARTICLE V

                            COVENANTS OF THE COMPANY

        The Company covenants and agrees with the Purchaser that so long as the
Purchaser (or an affiliate thereof) owns at least 25 % of the shares of Series
A-2 Preferred purchased by the Purchaser:

          SECTION 5.1. Financial Statements, Reports, etc. The Company shall
furnish to each holder of Series A-2 Preferred:

               (a) as soon as available, but in any event within 90 days after
        the end of each fiscal year of the Company, a copy of the consolidated
        balance sheet of the Company and its subsidiaries with which it is
        consolidated for financial statement purposes ("Subsidiaries") as at the
        end of such year and the related consolidated statements of income,
        stockholders' equity and cash flows for such year, setting forth in each
        case comparisons to the figures for the previous year, reported on
        without a "going concern" or like qualification or exception, or
        qualification arising out of the scope of the audit, by Ernst & Young or
        other independent certified public accountants of nationally recognized
        standing;

               (b) as soon as available, but in any event not later than 30 days
        after the end of each month of each fiscal year of the Company, the
        unaudited consolidated balance sheet 


                                       13
   18
        of the Company and its Subsidiaries as at the end of such month and the
        related unaudited consolidated statements of income, stockholders'
        equity and cash flows of the Company and its Subsidiaries for such month
        and the portion of the fiscal year through the end of such month,
        setting forth in each case comparisons to the figures for the previous
        year certified by an executive officer of the Company (a "Responsible
        Officer") as being fairly stated in all material respects (subject to
        normal year-end audit adjustments);

               (c) all such financial statements shall be complete and correct
        in all material respects and shall be prepared in reasonable detail and
        in accordance with GAAP applied consistently throughout the periods
        reflected therein and with prior periods (except as approved by such
        accountants or officer, as the case may be, and disclosed therein) and
        shall be accompanied by a management discussion and analysis in respect
        of the fiscal periods reported on therein;

               (d) concurrently with the delivery of the financial statements
        referred to in clause (a) above, a certificate of the independent
        certified public accountants reporting on such financial statements
        stating that in making the examination necessary therefor no knowledge
        was obtained of any Default or Event of Default (as such terms are
        defined in the notes (the "Notes") issued pursuant to the Note
        Agreement), except as specified in such certificate;

               (e) concurrently with the delivery of the financial statements
        referred to in clause (a) or clause (b) above, a certificate of a
        Responsible Officer stating that, to the best of such officer's
        knowledge, the Company during such period and as of the date of such
        certificate has observed or performed all of its covenants and other
        agreements, and satisfied every condition, contained in this Agreement
        to be observed, performed or satisfied by it, and that such officer has
        obtained no knowledge of any Default or Event of Default during such
        period or on or prior to the date of such certificate except as
        specified in such certificate;

               (f) not later than 30 days prior to the end of each fiscal year
        of the Company, a copy of the projections by the Company for the
        operating budget and cash flow budget of the Company and its
        Subsidiaries for the succeeding fiscal year, such projections to be
        accompanied by a certificate of a Responsible Officer to the effect that
        such projections have been prepared on the basis of sound financial
        planning practice and that such officer has no reason to believe they
        are incorrect or misleading in any material respect;

               (g) within 5 days after the same are sent, copies of all
        financial statements and reports which the Company sends to its other
        stockholders, and within 5 days after the same are filed, copies of all
        financial statements and reports which the Company may make to, or file
        with, the Securities and Exchange Commission or any successor or
        analogous governmental authority;

               (h) promptly upon receipt thereof, any additional reports,
        management letters or other detailed information concerning significant
        aspects of the Company's operations 



                                       14
   19

        or financial affairs given to the Company by its independent certified
        public accountants (and not otherwise contained in other materials
        provided hereunder);

               (i) during the month of October in each calendar year, a report
        of a reputable insurance broker with respect to the Company's insurance;

               (j) promptly, and in any case within five business days
        thereafter, written notice of the commencement of any action, suit or
        proceeding before any court or governmental department, commission,
        board, bureau, agency or instrumentality, domestic or foreign, affecting
        the Company or any of its Subsidiaries, and of any material adverse
        development in connection with any of the foregoing, in each case
        described in reasonable detail (including a description of the parties,
        the venue and the nature of the claim); and

               (k) promptly, such additional financial and other information as
        the holder of Series A-2 Preferred may from time to time reasonably
        request.

        SECTION 5.2.  Corporate Existence.  The Company shall maintain its
corporate existence, rights and franchises in full force and effect.

        SECTION 5.3. Properties, Business, Insurance. The Company shall maintain
with financially sound and reputable insurers, insurance against such casualties
and contingencies and of such types and in such amounts and with such deductible
as are customary for companies similarly situated, including but not limited to
fire and other risks insured against by extended coverage, product liability
insurance, key person insurance and public liability insurance against claims
for personal injury or death or property damage occurring upon, in, about or in
connection with the use of any properties owned, occupied or controlled by the
Company, which insurance shall be deemed by the Company to be sufficient; and
maintain workers' compensation insurance and such other insurance as may be
required by law. The Company shall keep all property useful and necessary in its
business in good working order and condition in accordance with industry
standards and applicable law.

        SECTION 5.4. Inspection, Consultation and Advice. The Company shall
permit the Purchaser at the expense of the Purchaser (unless occasioned by a
default by the Company of its obligations under this Agreement, or the terms of
the Series A-2 Preferred Stock, and then at the Company's expense), to visit and
inspect any of the properties of the Company, examine its books and take copies
and extracts therefrom, discuss the finances and accounts of the Company with
its officers, employees and public accountants (and the Company hereby
authorizes said accountants to discuss with the Purchaser such finances and
accounts), and consult with and advise the management of the Company and its
independent certified public accountants as to its finances and accounts, all at
reasonable times and upon reasonable notice.

        SECTION 5.5. Restrictive Agreements Prohibited. The Company shall not
become a party to any agreement which by the terms thereof or as a result of the
performance thereof restricts the Company's performance of, or ability to
perform, this Agreement or the Charter.



                                       15
   20

         SECTION 5.6. Board of Directors Meetings. The Company shall use its
best efforts to ensure that meetings of its Board of Directors are held at least
semi-annually.

        SECTION 5.7. Compliance with Laws. The Company shall comply with all
applicable laws, rules, regulations and orders, and each of its Contractual
Obligations (as defined in the Notes), in each case to the extent any such
noncompliance could materially adversely affect its business or condition,
financial or otherwise.

        SECTION 5.8. Keeping of Records and Books of Account. The Company shall
keep adequate records and books of account, in which complete entries will be
made in accordance with generally accepted accounting principles consistently
applied, reflecting all financial transactions of the Company, and in which, for
each fiscal year, all proper reserves for depreciation, depletion, obsolescence,
amortization, taxes, bad debts and other purposes in connection with its
business shall be made.

        SECTION 5.9. Maintaining Nature of Business. The Company will remain in
the business of researching and developing, manufacturing and distributing
biotechnology and healthcare products.

        SECTION 5.10. Obligations and Taxes. The Company shall pay when due all
of its indebtedness and obligations promptly and in accordance with their terms
and pay and discharge promptly all taxes, assessments and governmental charges
or levies imposed upon it or its income or profits or in respect of its
properly, before the same shall become in default, as well as all lawful claims
for labor and supplies or otherwise which, if unpaid, might become a lien or
charge upon such properties or any part thereof, provided, however, that the
Company shall not be required to pay and discharge or to cause to be paid and
discharged any indebtedness, obligation, tax, assessment, charge, levy or claim
so long as the validity or amount thereof shall be contested in good faith by
appropriate proceedings and the Company shall have set aside on its books such
reserves as may be required by generally accepted accounting principles with
respect to any such tax, assessment, charge, levy or claim so contested.

        SECTION 5.11. Further Issuances of Series A-2 Preferred. The Company
shall not, directly or indirectly, issue, offer to sell, effect any sale or
otherwise dispose of by any means any shares of Series A-2 Preferred or rights
to acquire such shares or securities convertible into or exchangeable for such
shares without the prior written consent of the majority of the holders of the
Series A-2 Preferred.

        SECTION 5.12. Notices. The Company shall promptly give notice to each
holder of Series A-2 Preferred of:

               (a) the occurrence of any Default or Event of Default;

               (b) any (1) default or event of default under any Contractual
        Obligation of the Company or any of its Subsidiaries or (2) litigation,
        investigation or proceeding which may exist at any time between the
        Company or any of its Subsidiaries and any Governmental Authority (as
        such term is defined in the Notes), which in either case, if 



                                       16
   21

        not cured or if adversely determined, as the case may be, could
        reasonably be expected to have a Material Adverse Effect (as such term
        is defined in the Notes);

               (c) any litigation or proceeding affecting the Company or any of
        its Subsidiaries in which the amount involved is $250,000 or more and
        not covered by insurance or in which injunctive or similar relief is
        sought;

               (d) the following events, as soon as possible and in any event
        within 30 days after the Company knows or has reason to know thereof:
        (1) the occurrence or expected occurrence of any Reportable Event (as
        such term is defined in the Notes) with respect to any Plan, a failure
        to make any required contribution to a Plan (as such term is defined in
        the Notes), the creation of any Lien in favor of the PBGC (as such term
        is defined in the Notes) or a Plan or any withdrawal from, or the
        termination, Reorganization or Insolvency (as such terms are defined in
        the Notes) of, any Multiemployer Plan (as such term is defined in the
        Notes) or (2) the institution of proceedings or the taking of any other
        action by the PBGC or the Company or any Commonly Controlled Entity (as
        such term is defined in the Notes) or any Multiemployer Plan with
        respect to the withdrawal from, or the terminating, Reorganization or
        Insolvency of, any Plan;

               (e) any material adverse change in the business, operations,
        property, condition (financial or otherwise) or prospects of the Company
        and its Subsidiaries taken as a whole;

               (f) any application or registration relating to any material
        patent or trademark of the Company or any of its Subsidiaries becoming
        abandoned or dedicated, or of any adverse determination or development
        (including, without limitation, the institution of, or any such
        determination or development in, any proceeding in the United States
        Patent and Trademark Office or any court or tribunal in any country)
        regarding the Company's or Bartels' ownership of any material patent or
        trademark or its right to register the same or to keep and maintain the
        same.

Each notice pursuant to this Section 5.12 shall be accompanied by a statement of
a Responsible Officer setting forth details of the occurrence referred to
therein and stating what action the Company proposes to take with respect
thereto.

        SECTION 5.13. Environmental Matters. (a) The Company shall comply with,
and ensure compliance by all tenants and subtenants, if any, with, all
applicable Environmental Laws (as such term is defined in the Notes) and obtain
and comply with and maintain, and ensure that all tenants and subtenants obtain
and comply with and maintain, any and all licenses, approvals, notifications,
registrations or permits required by applicable Environmental Laws.

               (b)    Conduct and complete all investigations, studies, 
        sampling and testing, and all remedial, removal and other actions
        required under Environmental Laws and promptly comply with all lawful
        orders and directives of all Governmental Authorities regarding
        Environmental Laws.


                                       17
   22

        SECTION 5.14. The Exchange Notes; Security Interest; Guaranty. (a)
Immediately upon the issuance by the Company of one or more notes (the "Exchange
Notes") pursuant to the Certificate of Designation (which Exchange Notes shall
be in substantially the form of Exhibit C hereto), the Company and Bartels agree
to execute such agreements and other documents such that payment of the Exchange
Notes is guaranteed by Bartels and the Exchange Notes are secured by all of the
assets of the Company (including all intellectual property and the assets and
stock of subsidiaries formed after the date of this Agreement), with the
obligation of Bartels under the aforementioned guaranty to be secured by all of
the assets of Bartels (including all intellectual property), all the extent
practicable, to the same extent (limited only to the extent not then currently
possible) as payment of the Notes has been guaranteed and secured pursuant to
the:

                      (i) Junior Subordinated Security Agreement between the
               Company, Bartels and Purchaser dated as of June 21, 1996;

                      (ii) Junior Subordinated Pledge Agreement between the
               Company and Purchaser dated as of June 21, 1996;

                      (iii) Junior Subordinated subsidiary Guaranty by Bartels
               in favor of Purchaser, as Lender, dated as of June 21, 1996;

                      (iv) Agreement (Patent) between the Company, as Grantor,
               and Purchaser, as Lender, dated as of June 21, 1996;

                      (v) Agreement (Trademark) between the Company, as Grantor,
               and Purchaser as Lender, dated as of June 21, 1996;

                      (vi) Agreement (Patent) between Bartels, as Grantor, and
               Purchaser, as Lender, dated as of June 21, 1996;

                      (vii) Agreement (Trademark) between Bartels, as Grantor,
               and Purchaser, as Lender, dated as of June 21, 1996;

               (b) The Company and Bartels further agree to immediately take all
        action necessary to perfect such security interests; provided, however,
        that the preceding undertaking by the Company and Bartels shall not be
        deemed to be a covenant by either of them that such security interests
        shall have the same priority as those that have been heretofore securing
        payment of the Notes.

        SECTION 5.15. Waivers. The Company agrees that it will not enter into a
waiver with respect to a default under an agreement for borrowed money if such
waiver provides that cash dividends may not be paid under the terms of the
Certificate of Designation after the date on which the default has been cured
(other than a deemed cure of such default by reason of the existence of the
waiver).


                                       18
   23

        SECTION 5.16. Payment of Dividends.  The Company agrees to pay all 
dividends due to Northstar High Total Return Fund as follows:

        For cash payments:
        CTC NJ
        ABA No. 031207526
        BNF=TRUST
        OBI=NORTHSTAR HIGH TOTAL RETURN FUND

        For payments in kind:
        Custodial Trust Corp.
        101 Carnegie Center
        Princeton, NJ  08540
        Attn.:  Ms. Ann Pedersen

        SECTION 5.17. Further Assurances. The Company and the Purchaser hereby
agree to take such further action as shall be commercially and reasonably
necessary to provide each party hereto with the benefits intended to be granted
by this Agreement to such party.


                                   ARTICLE VI

                                  MISCELLANEOUS

        SECTION 6.1. Expenses. (a) Except to the extent provided in Section
4.6, each party hereto will pay its own expenses in connection with the
transactions contemplated hereby whether or not such transactions shall be
consummated.

               (b) The Company will also pay, and will save the Purchaser
        harmless from, any and all liabilities with respect to any taxes, and
        interest and penalties thereon (other than taxes which are measured
        solely by the income of the Purchaser), which may be payable in respect
        of the execution and delivery of this Agreement, or the issue of the
        Series A-2 Preferred Stock.

        SECTION 6.2. Survival of Agreements. Unless otherwise expressly stated
herein, or in any certificate or instrument delivered to the Purchaser pursuant
thereto, all covenants and agreements, made herein, or any certificate or
instrument delivered to the Purchaser pursuant to or in connection with this
Agreement shall survive the execution and delivery of this Agreement, and the
issuance, sale and delivery of the shares of the Series A-2 Preferred. All
statements contained in any certificate or other instrument delivered by the
Company hereunder or thereunder or in connection herewith or therewith shall be
deemed to constitute representations and warranties made by the Company.

        SECTION 6.3. Brokerage. Each party hereto will indemnify and hold
harmless the other against and in respect of any claim for brokerage or other
commissions relative to this Agreement or to the transactions contemplated
hereby, based in any way on agreements, 



                                       19
   24
arrangements or understandings made or claimed to have been made by such party
with any third party.

        SECTION 6.4. Parties in Interest. All representations, covenants and
agreements contained in this Agreement by or on behalf of any of the parties
hereto shall bind and inure to the benefit of the respective successors and
assigns of the parties hereto whether so expressed or not. Without limiting the
generality of the foregoing, all representations, covenants and agreements
benefiting the Purchaser shall inure to the benefit of any and all subsequent
holders from time to time of shares of Series A-2 Preferred.

        SECTION 6.5. Notices; Payment of Dividends. All notices, requests,
consents and other communications hereunder shall be in writing and shall be
delivered in person or mailed by certified or registered mail, return receipt
requested, or telexed in the case of non U.S. residents, addressed as follows:

               (a)    if to the Company, at Intracel Corporation, 1871 N.W. 
        Gilman Blvd., Issaquah, WA 98027, Attention: Simon R. McKenzie, with a
        copy to Joseph W. Bartlett, Morrison & Foerster LLP, 1290 Avenue of the
        Americas, New York, New York 10104; and

               (b) if to the Purchaser, at the address set forth beneath the
        Purchaser's name; or, in any such case, at such other address or
        addresses as shall have been furnished in writing by such party to the
        others.

        So long as the Purchaser or any affiliate of the Purchaser, or a nominee
of either, shall be the holder of Series A-2 Preferred, and in addition to any
provision contained in the Articles of Organization with respect to the method
of payment of dividends, the Company will pay all dividends on Series A-2
Preferred owned by such person by the method and at the addresses specified for
such purposes on the attached Schedule I, or by such other method or at such
other address as such person shall have specified to the Company in writing for
such purposes. The Company shall accord the benefits of this paragraph to any
institutional purchaser which shall have purchased shares of Series A-2
Preferred directly from the Purchaser or an affiliate of the Purchaser.

        SECTION 6.6. Replacement of Certificates. Upon receipt of evidence
reasonable satisfactory to the Company of the loss, theft, destruction or
mutilation of any certificate evidencing ownership of shares of Series A-2
Preferred by the Purchaser or an affiliate of the Purchaser, or a nominee of
either (a "Certificate" for purposes of this Section 6.6) and, in the case of
loss, theft or destruction of any Certificate upon delivery of an indemnity bond
in such reasonable amount as the Company may determine (but if such holder is an
insurance company, an unsecured indemnity agreement from such holder shall
suffice) or, in the case of mutilation upon surrender of such Certificate for
cancellation to the Company at its principal office, the Company at its expense
will execute and deliver in lieu thereof a new Certificate for the same number
of shares as were evidenced by such lost, stolen, destroyed or mutilated
Certificate which 



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shall be in such form and tenor as not to cause any loss of accrued dividends on
the shares evidenced by the lost, stolen, destroyed or mutilated Certificate.

        SECTION 6.7. Governing Law. This Agreement shall be construed and
enforced in accordance with, and governed by, the laws of the State of New York,
regardless of the jurisdiction of creation or domicile of the Company or its
successors or of the Purchaser (without giving effect to such jurisdiction's
choice of law principles that would result in the application of any law other
than that of the State of New York), except that the filing, perfection, effect
of perfection and enforcement of security interests and liens in other
jurisdictions shall be governed by the laws of the applicable jurisdictions in
accordance with the Uniform Commercial Code as then in effect under the laws of
the respective state of reference.

        SECTION 6.8. Entire Agreement. This Agreement, including the Schedules
and Exhibits hereto, constitutes the sole and entire agreement of the parties
with respect to the subject matter hereof. All Schedules and Exhibits hereto are
hereby incorporated herein by reference.

        SECTION 6.9. Submission to Jurisdiction; Waivers. Each of the Company
and the Purchaser hereby irrevocably and unconditionally:

               (a) submits for itself and its property in any legal action or
        proceeding relating to this Agreement, or for recognition and
        enforcement of any judgment in respect thereof, to the non-exclusive
        general jurisdiction of the Courts of the State of New York, the courts
        of the United States of America for the Southern District of New York,
        and appellate courts from any thereof;

               (b) consents that any such action or proceeding may be brought in
        such courts and waives any objection that it may now or hereafter have
        to the venue of any such action or proceeding in any such court or that
        such action or proceeding was brought in an inconvenient court and
        agrees not to plead or claim the same;

               (c) agrees that service or process in any such action or
        proceeding may be effected by mailing a copy thereof by registered or
        certified mail (or any substantially similar form of mail), postage
        prepaid, to the Company at its address set forth in Section 6.5 or at
        such other address of which the Purchaser shall have been notified
        pursuant thereto;

               (d) agrees that nothing herein shall affect the right to effect
service of process in any other manner permitted by law or shall limit the right
to sue in any other jurisdiction; and

               (e) waives, to the maximum extent not prohibited by law, any
        right it may have to claim or recover in any legal action or proceeding
        referred to in this subsection any special, exemplary, punitive or
        consequential damages.

        SECTION 6.10. Counterparts.  This Agreement may be executed in two or 
more counterparts, each of which shall be deemed an original, but all of which
together shall constitute one and the same instrument.



                                       21
   26

        SECTION 6.11. Amendments. This Agreement may not be amended or modified,
and no provisions hereof may be waived, without the written consent of the
Company and the holders of at least two-thirds of the outstanding shares of the
Series A-2 Preferred.

        SECTION 6.12. Severability. If any provision of this Agreement shall be
declared void or unenforceable by any judicial or administrative authority, the
validity of any other provision and of the entire Agreement shall not be
affected thereby.

        SECTION 6.13. Titles and Subtitles. The titles and subtitles used in
this Agreement are for convenience only and are not to be considered in
construing or interpreting any term or provision of this Agreement.




                                       22
   27

        IN WITNESS WHEREOF, the Company and the Purchaser have executed this
Agreement as of the day and year first above written.



                                         
                                            INTRACEL CORPORATION


[Corporate Seal]                            By:
                                               -------------------------------------------
                                                   Name:    Simon R. McKenzie
                                                   Title:   President and Chief Executive
                                                            Officer


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

- -----------------------------------
Name:      Cheryl Cataldo                   SOLELY FOR PURPOSES OF SECTION 5.14
Title:     Clerk                            BARTELS, INC.


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


                                            PURCHASER:
                                            NORTHSTAR HIGH TOTAL RETURN FUND


                                            By:
                                               -------------------------------------------
                                                Name:     Thomas Ole Dial
                                                Title:    Vice President
                                                Address:  2 Pickwick Plaza, c/o Thomas Ole
                                                          Dial, Greenwich, CT 06803
                                                          Attention:  Michael Graves

                                                copy to:  Karen Wiedemann, Esq,
                                                          Reboul, MacMurray, Hewitt,
                                                          Maynard & Kristol
                                                          45 Rockefeller Plaza
                                                          New York, New York



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