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                                                                   EXHIBIT 10.25

                    INTELLECTUAL PROPERTY SECURITY AGREEMENT

     This Intellectual Property Security Agreement (the "Security Agreement")
is made and entered into as of this 13th day of August, 1996, by and among
PerImmune Holdings, Inc., whose address is 1330 Piccard Drive, Rockville,
Maryland 20850-4396 ("Holdings"), PerImmune, Inc. ("PerImmune"), Akzo Nobel
Pharma International, B.V., a corporation formed under the laws of the
Netherlands ("Pharma"), Organon Teknika Corporation ("OTC" together with
Pharma, the "Secured Parties") and Pharma, in its capacity as Collateral Agent
hereunder ("Collateral Agent"). 

                                    RECITAL

     WHEREAS, pursuant to that certain Promissory Note (the "Purchase Price
Note") dated as of August 2, 1996, made by Holdings pursuant to Section 2.2 of
the Stock Purchase Agreement, dated as of July 1, 1996 (as amended, modified or
supplemented from time to time) (the "Stock Purchase Agreement"), Holdings has
promised to pay to OTC an amount equal to Nine Million Two Hundred Thirty-four
Thousand Nine Hundred Thirty-five Dollars ($9,234,935).

     WHEREAS, pursuant to a certain credit agreement, dated as of August 2,
1996 (as amended, modified or supplemented from time to time) (the "Credit
Agreement") between PerImmune and OTC, OTC has agreed to make to or for the
account of PerImmune certain loans up to Three Million Six Hundred Thousand
Dollars ($3,600,000) as may be increased by One Million Eight Hundred Thousand
Dollars ($1,800,000) in accordance with such Credit Agreement, to be evidenced
by PerImmune's Secured Promissory Note (the "Secured Note").

     WHEREAS, pursuant to a certain working capital facility, dated as of
August 2, 1996 (as amended, modified or supplemented from time to time) (the
"Working Capital Facility") between PerImmune and OTC, OTC has agreed to make
to or for the account of PerImmune certain loans up to Two Million Eight
Hundred Seventy-one Thousand Five Hundred Thirty-two Dollars ($2,871,532) to be
evidenced by PerImmune's Working Capital Secured Note (the "Working Capital
Note").

     WHEREAS, pursuant to a certain intellectual property agreement by and
between Holdings and Pharma dated as of August 2, 1996 (the "Intellectual
Property Agreement") whereby, in consideration of the transfer to Holdings of
certain patents and patent applications and other intellectual property,
Holdings has agreed to make to Pharma certain future payments.

     WHEREAS, the parties hereto intend that the respective obligations of
Holdings under the Purchase Price Note and under the Intellectual Property
Agreement, and of PerImmune under the Credit Agreement and the Working Capital
Facility shall be secured by a pledge of Holdings' right, title and interest
in the Collateral (as defined herein).


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     WHEREAS, the parties hereto intend that Pharma act as Collateral Agent for
the equal and ratable benefit of the Secured Parties.

                                   AGREEMENT

     Now therefore, in consideration of the above recitals and the agreement
hereinafter set forth, the parties hereto agree as follows:

     1.   Creation of Security Interest. In order to secure the payment and
performances of all Obligations, Holdings hereby grants to the Collateral
Agent, for the equal and ratable benefit of the Secured Parties, a security
interest in all of Holdings' right, title and interest in and to the collateral
described in Section 2 below (the "Collateral") in order to secure the payment
and performance of the respective obligations of PerImmune and Holdings to
Secured Parties described in Section 3 below.

     2.   Collateral.

               (a)  The Collateral under this Security Agreement shall mean (i)
     those certain patents and patent applications set forth in Schedule A
     attached hereto (including, without limitation, all divisions,
     continuations, continuations-in-part, reissues, renewals or extensions
     thereof) (the "Patents") and (ii) those certain trademarks set forth on
     Schedule B attached hereto (including all goodwill of Holdings' business
     connected with the use of, and symbolized by, any and all such trademarks)
     (the "Trademarks").

               (b)  If, before the termination of this Agreement, Holdings shall
     become entitled to the benefit of any patent or patent application for any
     division, continuation, continuation-in-part, reissues, renewal or
     extension of a Patent, the provisions of Section 1 shall automatically
     apply thereto and Holdings shall give to the Collateral Agent prompt notice
     thereof in writing. Holdings authorizes the Collateral Agent to modify this
     Agreement by amending Schedule A to reflect the addition of such patents or
     patent applications.

     3.   Secured Obligations of Debtor. The Collateral secures and shall
hereafter secure (i) the payment by PerImmune to OTC of all indebtedness now or
hereafter owed to OTC by PerImmune under the Credit Facility, the Secured Note,
the Working Capital Facility, the Working Capital Note and this Security
Agreement together with any interest thereon and extensions, modifications and
renewals thereof, and (ii) the payment of Holdings (a) to OTC of all
indebtedness owed to OTC under the Purchase Price Note, and (b) to Pharma of
all amounts due pursuant to Section 2.2(a)(i) and Section 2.2(b) of the
Intellectual Property Agreement prior to the termination of this Agreement and
(iii) performance by Holdings of all other obligations and the discharge of all
other liabilities to Secured Parties of every kind and character, direct or
indirect, absolute or contingent, due or to become due, now existing or
hereafter arising, joint, several and joint and several, created under this
Security Agreement (together, the "Obligations"). All payments and performance
shall be in



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accordance with the terms under which said indebtedness, obligations and
liabilities were or are hereafter incurred or created.

          4.   The Collateral Agent. Pharma is hereby appointed as the
Collateral Agent to serve in such capacity until a successor is duly appointed.
The Collateral Agent hereby accepts such appointment and acknowledges that it
is acting in such capacity for the benefit of the Secured Parties.

          5.   Restrictions on Future Agreements. Holdings agrees that, except
as set forth in Section 8 hereof, until the Obligations shall have been
satisfied in full and this Agreement shall have been terminated, Holdings will
not, without the Collateral Agent's prior written consent, (a) enter into any
agreement that is inconsistent with Holdings' obligations under this Agreement
or (b) sell, pledge, license or assign its interest in any of the Collateral.

          6.   Defaults and Remedies

          Holdings shall be in default under this Agreement upon the happening
of any of the following events:

               (a)  PerImmune fails to pay or perform any of the obligations
owed to OTC in accordance with the terms upon which such obligations were
incurred or created under the Secured Note or the Working Capital Note and such
failure continues thereafter for a period of thirty (30) days after such sum
becomes due and owing.

               (b)  Holdings fails to pay or perform any of the obligations
owed to OTC under the Purchase Price Note or to Pharma under Section 2.2(a)(i)
and Section 2.2(b) of the Intellectual Property Agreement in accordance with
the respective terms upon which such obligation was incurred or created and
such failure continues thereafter, in the case of the Purchase Price Note, for
a period of thirty (30) days after such sum becomes due and owing, and in the
case of payments under Section 2.2(a)(i) and Section 2.2(b) of the Intellectual
Property Agreement, for a period of thirty (30) days after written notice to
Holdings that such sums are due and owing.

               (c)  All or any portion of the Collateral is seized or levied by
writ of attachment, garnishment, execution or otherwise and such seizure or
levy is not released within fifteen (15) days thereof.

               (d)  PerImmune executes a general assignment for the benefit of
its credits, ceases to conduct its business in the ordinary course as it is now
conducted, convenes any meeting of its creditors, becomes insolvent, admits in
writing its insolvency or inability to pay its debts, or is unable to pay or is
generally not paying its debts as they become due.

               (e)  Holdings executes a general assignment for the benefit of
its creditors, ceases to conduct its business in the ordinary course as it is
now


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     conducted, convenes any meeting of its creditors, becomes insolvent, admits
     in writing its insolvency or inability to pay its debts, or is unable to
     pay or is generally not paying its debts as they become due.

          (f)  A receiver, trustee, custodian or agent is appointed to take
     possession of all or any substantial portion of PerImmune's assets.

          (g)  A receiver, trustee, custodian or agent is appointed to take
     possession of all or any portion of the Collateral or all or any
     substantial portion of Holdings' assets.

          (h)  Any case or proceeding is voluntarily commenced by PerImmune
     under any provision of the Federal Bankruptcy Code or any other federal or
     state law relating to debtor rehabilitation, insolvency, bankruptcy,
     liquidation or reorganization, or any such case or proceeding is
     involuntarily commenced against PerImmune. 

          (i)  Any case or proceeding is voluntarily commenced by Holdings
     under any provision of the Federal Bankruptcy Code or any other federal or
     state law relating to debtor rehabilitation, insolvency, bankruptcy,
     liquidation or reorganization, or any such case or proceeding is
     involuntarily commenced against Holdings.

Upon such default hereunder, Collateral Agent, acting for the benefit of the
Secured Parties, shall have the remedies of a secured party under the
applicable Uniform Commercial Code and as set forth in Section 10, PerImmune or
Holdings, as appropriate, shall reimburse the Collateral Agent for all
reasonable costs and reasonable attorney's fees incurred by Collateral Agent in
pursuing any remedies, which costs and fees are also Obligations secured
hereunder.

          7.   Use and Pledge of Pledged Collateral. Unless an event of default
shall have occurred, Collateral Agent, on behalf of Secured Parties, shall from
time to time execute and deliver, upon written request of Holdings, any and all
instruments, certificates or other documents, in the form so requested,
necessary or appropriate in the reasonable judgment of Holdings to enable
PerImmune to continue to exploit, license, use, enjoy and protect the
Collateral throughout the world provided such instrument, certificate or
document does not conflict with nor diminish the rights of the Collateral Agent
or the Secured Parties hereunder and provided that Holdings gives adequate
assurance that the proceeds of the proposed transaction will be applied toward
any payment obligations that will be due and owing to Pharma under the
Intellectual Property Agreement as a result of such transaction. The parties
hereto each acknowledges that this Agreement is intended for the benefit of the
Collateral Agent on behalf of the Secured Parties and to grant a security
interest in and lien upon the Collateral and that, notwithstanding the
provisions of Section 10 hereof, shall not constitute or create a present
assignment of the Collateral.

     8.   Transfer of Collateral. The parties hereto each recognize and
acknowledge the right of Holdings under the Intellectual Property Agreement to
transfer and


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assign to PerImmune all of Holdings' rights, title and interest in the
Collateral, and the Collateral Agent and the Secured Parties agree to promptly
execute and deliver all further documents and instruments, and to take all
further actions that may be necessary or that Holdings or PerImmune may
request, in order to reflect or acknowledge such transfer. Upon consummation of
the transfer of the Collateral, PerImmune shall be bound by all terms of this
Agreement.

     9.   Termination of Agreement. This Security Agreement shall terminate
upon the earlier of (i) full and final payment and performance of all
indebtedness and obligations secured hereunder, and (ii) in the absence of a
default hereunder, two (2) years from the date of this Security Agreement
(provided that such term shall be extended for the length of any cure period if
an event has occurred which would constitute a default if not for the
additional time allowed for the cure period). At such time, Collateral Agent
shall promptly execute and deliver to Holdings all deeds, assignments and other
instruments (including termination statements on Form UCC-3 and documents
suitable for recordation in the United States Patent and Trademark Office, the
United States Copyright Office or similar domestic or foreign authority)
acknowledging the termination of this Agreement and the release of the security
interest in the Collateral created hereunder.

     10.  Conditional Assignment.

          10.1 In order to induce the Secured Parties to provide funds and
credit as set forth above, Holdings has agreed to make the conditional
assignment described in this Section 10 to the Collateral Agent of the Patents
and the Trademarks to secure Holdings' and PerImmune's performance of their
Obligations pursuant to this Agreement.

          10.2 Holdings hereby conditionally grants, assigns and conveys to the
Collateral Agent the entire right, title and interest in and to the Patents and
the Trademarks. The parties hereto acknowledge that the conditional assignment
pursuant to this Section 10.2 shall have no effect, and the Collateral Agent
shall have no ownership interest in the Patents and the Trademarks pursuant to
this Section 10.2, unless and until there shall have occurred an event of
default under Section 6 above. Upon termination of this Agreement pursuant to
Section 9 above, the conditional assignment pursuant to this Section 10.2 shall
be terminated, and thereafter shall not be given any effect. Upon the
occurrence of an event of default hereunder, any and all rights, residual,
inchoate, by license or of any kind, that Holdings may have in the Patents and
the Trademarks shall be deemed assigned to Collateral Agent, which shall then
have the entire right, title and interest in and to the Patents and the
Trademarks, free of any obligation to Holdings, by effect of this conditional
assignment.

          10.3 If, before the Obligations shall have been satisfied in full,
Holdings shall become entitled to the benefit of any patent application or
patent for any reissue, division, continuation, renewal, extension, or
continuation-in-part of any Patent or any improvement on any Patent, the
provisions of Section 10.2 shall automatically apply thereto and Holdings shall
give to Collateral Agent prompt notice thereof in writing. Holdings



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authorizes Collateral Agent to modify this Agreement by amending Schedule A to
include any such future patents and patent applications.

     11.  Miscellaneous Provisions

          11.1 Notices. Notices, requests and other communications hereunder
shall be in writing and may be delivered personally or sent by telegram, telex
or first class mail to the parties addressed as follows:

          To PerImmune:

               PerImmune, Inc.
               1330 Piccard Drive
               Rockville, MD 20850-4396
               Attention: Michael G. Hanna, Jr.

          To Holdings:

               PerImmune Holdings, Inc.
               1330 Piccard Drive
               Rockville, MD 20850-4396
               Attention: Michael G. Hanna, Jr.

          To Pharma:

               Akzo Nobel Pharma International, B.V.
               P.O. Box 20 5345 BH
               Oss, The Netherlands
               Attn: General Counsel

          To OTC:

               Organon Teknika Corporation
               100 Akzo Avenue
               Durham, N.C. 27712
               Attn: President

Such notices, requests and other communications sent as provided above shall be
effective when received by the addressee thereof, but if sent by registered or
certified mail, postage prepaid, shall be effective three (3) business days
after being deposited in the United States mail. The parties hereto may change
their addresses by giving notice thereof to the other parties hereto in
conformity with this section.

          11.2 Headings. All headings have been inserted for convenience only
and shall not affect the meaning or interpretation of this Security Agreement
or any provision hereof.



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          11.3  Governing Law. This Security Agreement shall be construed in
accordance with and all disputes hereunder shall be governed by the laws of the
State of Maryland.

          11.4  Binding Agreement. All rights of Secured Parties hereunder
shall inure to the benefit of each of its successors and assigns. PerImmune
shall not assign any of its interest under this Security Agreement without the
prior written consent of Secured Parties.

          11.5  Definitions. All terms not defined herein shall have the
meaning set forth in the applicable Uniform Commercial Code, except where the
context otherwise requires.

          11.6  Entire Agreement. This Security Agreement, the Credit
Agreement, the Working Capital Agreement, the Purchase Price Note, the Secured
Note and the Working Capital Note executed in connection herewith, are intended
by the parties as a final expression of their agreement and are intended as a
complete and exclusive statement of the terms and conditions thereof.

          11.7  Severability. If any provision of this Security Agreement
should be found to be invalid or unenforceable, all of the other provisions
shall nonetheless remain in full force and effect to the maximum extent
permitted by law.

          11.8  Jurisdiction.  Pharma (including in its capacity as Collateral
Agent) hereby irrevocably submits for the benefit of PerImmune and Holdings to
the jurisdiction of the federal district courts located in the State of
Maryland in connection with any controversy, suit, action or proceeding which
may arise out of or in connection with this Security Agreement and the
transactions contemplated hereby. Pharma (including in its capacity as
Collateral Agent) hereby irrevocably waives any objection which it might now or
hereafter have to the courts referred to in the preceding sentence being
nominated as the forum to hear and determine any controversy, suit, action or
proceeding which may arise out of or in connection with this Security Agreement
and the transactions contemplated hereby, on the basis of improper venue,
inconvenient forum or otherwise, and agrees not to claim that any such court is
not a convenient or appropriate forum.

          11.9  Agent for Service of Process.

                (a) In connection with this Security Agreement and the
     transactions contemplated hereby, Pharma (including in its capacity as
     Collateral Agent) hereby agrees that the process by which any suit, action
     or proceeding is begun in the federal district courts located in the State
     of Maryland may be served on it by being delivered to Organon Teknika
     Corporation, 100 Akzo Avenue, Durham, N.C. 27712, Attn: President, and
     hereby irrevocably appoints such person as its agent for the service of
     process in connection therewith. If the appointment of the person
     mentioned in this Section 11.9 ceases to be effective, Pharma shall
     immediately appoint a further person to accept service of process on its
     behalf in Maryland and, failing such 



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     appointment within five (5) days after notice thereof to Pharma, Holdings
     or PerImmune shall be entitled to appoint such a person by notice to
     Pharma. Pharma (including in its capacity as Collateral Agent) further
     irrevocably consents to the service of process out of the aforementioned
     courts in any such action or proceeding by the mailing of copies thereof
     by registered or certified mail, postage prepaid, to Pharma, at the
     address identified for it in Section 11.1, such service to become
     effective ten (10) days after such mailing. Nothing contained herein shall
     affect the right to serve process in any other manner permitted by law.

                (b) The submission to the jurisdiction of the courts referred
     to above shall not (and shall not be construed so as to) limit the right
     of Holdings or PerImmune hereby to take proceedings against Pharma
     (including in its capacity as Collateral Agent) with respect to this
     Security Agreement and the transactions contemplated hereby in any other
     court of competent jurisdiction nor shall the taking of proceedings in any
     one or more jurisdictions preclude the taking of proceedings in any other
     jurisdiction (whether concurrently or not) if and to the extent permitted
     by applicable law.

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



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       IN WITNESS WHEREOF, the parties hereto have caused this Security
Agreement to be duly executed as of the day and year first above written.


                                   PerImmune, Inc.


                                   By    [SIG]
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                                   Title
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                                   PerImmune Holdings, Inc.


                                   By    [SIG]
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                                   Title
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                                   Akzo Nobel Pharma International, B.V.


                                   By    [SIG]
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                                   Title
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                                   Organon Teknika Corporation


                                   By    [SIG]
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                                   Title
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                                   Akzo Nobel Pharma International, B.V.
                                   as Collateral Agent


                                         By    [SIG]
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                                         Title
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