ASSIGNMENT FOR SECURITY
                                    (Patents)


STATE OF GEORGIA           )
                           )  ss.:
COUNTY OF FULTON           )


                  WHEREAS,   EDITEK,   INC.,   a   Delaware   corporation   (the
"Assignor"),  holds  Letters  Patent of the United States and  applications  for
Letters Patent of the United States as set forth on Exhibit A (collectively, the
"Patents"), and

                  WHEREAS,  the Assignor is the sole owner of the entire  right,
title  and  interest  in and to the  Patents  and the  inventions  which are the
subject matter thereof, and

                  WHEREAS,  Assignor  has  entered  into that  certain  Loan and
Security  Agreement,  dated of even date (as amended,  supplemented  or restated
from time to time,  the "Loan  Agreement"),  between  Assignor,  certain  of its
affiliates and HELLER FINANCIAL,  INC., a Delaware corporation  ("Lender"),  and
Lender  has, on the date  hereof,  made  certain  loans to or for the benefit of
Assignor and may make additional loans to or for the benefit of Assignor, and

                  WHEREAS,  pursuant  to the Loan  Agreement  and as a condition
precedent to the extension of the financial accommodations to or for the benefit
of the Assignor under the Loan  Agreement,  the Assignor has agreed to assign to
Lender  and to  grant  to  Lender  a  continuing  security  interest  in,  and a
continuing  lien on, all of the Assignor's  right,  title and interest in and to
the following (collectively the "Patent Collateral"),

                  (a)  the Patents, together with any reissue, continuation,
         continuation-in-part  or extension of any thereof, along  with all 
         rights,  benefits and privileges derived therefrom,

                  (b)  the inventions which are the subject matter thereof, and

                  (c)  all proceeds thereof, including, but not limited to, any
         claims and demands  arising  out of any  infringement  of the  Patents,
         including  the right to settle  disputes  concerning  such  claims  and
         demands.

                  NOW,  THEREFORE,  in order to induce Lender to consummate  the
financial accommodations to the Assignor provided for in the Loan Agreement, and
for other good and valuable consideration,  receipt and sufficiency of which are
hereby  acknowledged,  the  Assignor  does hereby  assign to Lender and grant to
Lender a continuing  security  interest in and a continuing



lien on, the entire right,  title and  interest  of Assignor  in and to the
Patent  Collateral.  The Patent  Collateral shall serve as collateral  security
to Lender for the payment and  performance  of the  Obligations  (as  such  term
is  defined  in the  Loan Agreement)  and  shall  constitute  a part of the
Collateral  (as such  term is defined  in the Loan  Agreement),  and shall be
subject to all of the terms and conditions of the Loan Agreement, which is
incorporated herein by reference.

                  Unless and until said lien and security interest is foreclosed
upon, Assignor (i) shall be deemed and is hereby licensed to remain in exclusive
and undisturbed  possession of the Patents,  (ii) shall  exclusively  retain all
rights to make, use, and sell the inventions claimed in the Patents,  to license
others under the Patents,  but only in a manner consistent with the preservation
of their current  substance,  validity,  registration and the security  interest
granted herein, and (iii) may bring suit for the infringement of the Patents and
to  retain  the  proceeds  of the  foregoing.  Lender  need not be  joined  as a
plaintiff in any such infringement suit; provided,  that should it be necessary,
in Lender's sole judgment,  that Lender be joined as an  indispensable  party or
true party in interest  in any such  infringement  suit,  Lender  shall,  at its
option, either

                  (1) appoint  Assignor  its attorney in fact for the purpose of
         prosecuting  such  infringement  suit  on the  express  condition  that
         Assignor  indemnify and hold Lender harmless for any liability incurred
         by Lender as a result of such appointment, or

                  (2) participate actively in the prosecution of such suit.

                  Assignor  further  agrees  (i)  that  while  a  secured  party
hereunder,  Lender  shall have no  obligation  or  responsibility  to protect or
defend the Patent  Collateral  and  Assignor  shall at its own expense  protect,
defend  and  maintain  the  same  to the  extent  reasonably  advisable  for its
business,  (ii) to use its best efforts to detect any  infringers  of the Patent
Collateral, to forthwith advise Lender in writing of infringements detected, and
protect,  defend and maintain the Patent Collateral  against any  infringements,
(iii) that if Assignor fails to comply with the foregoing  clauses (i) and (ii),
Lender  may do so in  Assignor's  name or in  Lender's  name  but at  Assignor's
expense,  and  Assignor  hereby  agrees to  reimburse  Lender for all  expenses,
including  reasonable   attorneys'  fees,  incurred  by  Lender  in  protecting,
defending and maintaining the Patent  Collateral owned by Assignor,  and (iv) to
use the Patents only in its businesses as they are presently conducted.

                  The  security  interest  in  the  Patent  Collateral   granted
hereunder  shall  remain  in full  force  and  effect  until  the  later  of the
termination  of the Loan Agreement and the payment and  satisfaction  in full of
the Obligations. At any time thereafter, Lender shall, if requested by Assignor,
execute  and  deliver  to  Assignor,   or  to  a  third  party  upon  Assignor's
instructions,  for filing with the United States Patent and Trademark Office and
in each  office  in which  any  financing  statement  relative  to the  security
interest  granted hereby may have been filed,  (i)  documentation  in accordance
with the rules and regulations of said office, (ii) termination statements under
the  Uniform  Commercial  Code and  (iii)  any  other  documentation  reasonably
requested by Assignor,  all as may be necessary to release Lender's  interest in
the Patent Collateral, and all at the cost and expense of Assignor.

                                     -2-



                  IN WITNESS WHEREOF, the Assignor has caused this Assignment to
be duly executed by its authorized officer or agent as of January ___, 1996.


                                                 EDITEK, INC.



                                                 By:

                                                 Title:

                                                 Attest:

                                                 Title:


                                                           [CORPORATE SEAL]



STATE OF GEORGIA  )
                  )  ss.:
COUNTY OF FULTON  )


                  On this ___ day of January,  1996,  before me personally  came
___________________  and  _____________________,  to me known,  who, being by me
duly   sworn,   did   depose   and  say  that   they  are,   respectively,   the
____________________and  _____________________  of EDITEK, INC., the corporation
described herein and which executed the foregoing instrument; that they know the
seal of said  corporation;  that the seal  affixed  to said  instrument  is such
corporate  seal;  that it was so affixed by order of the Board of  Directors  of
said corporation and that they signed thereto by like order.

                                               Sworn  to  and subscribed  before
                                               me this ___ day of January, 1996.


                                               Notary Public

                                                        [NOTARIAL SEAL]

                                               My Commission Expires:

                                       -3-



                                    EXHIBIT A




                                                                     Patent
                      Patent Name                                    Number                     Issue Date
                                                                                           
Rapid Radioimmunoassay Product and Method of Making and             4,399,229                    08/16/83
Using Same

Rotary Fluid Manipulator                                            4,938,927                    07/03/90

Rotary Fluid Manipulator                                            5,141,875                    08/25/92

Test Kit for Determining the Presence of Organic                    4,900,663                    02/13/90
Materials and Method of Utilizing Same

Test Kit for Determining the Presence of Organic                    5,240,844                    08/13/93
Materials and Method of Utilizing Same

Suspension Liquid Separator                                         4,696,797                    09/29/87

Multi-Layered Test Card for the Determination of                    5,202,268                    04/13/93
Substances in Liquids

Device for Analysis for Constituents in Biological Fluids           5,435,970                    07/25/90

Animal Cage and Method                                              4,593,650                    06/10/86
Method for Preserving Plated Media and Products                     4,709,819                    12/01/87



                                 -4-