ASSIGNMENT AGREEMENT


         THIS ASSIGNMENT AGREEMENT ("Assignment") is made and entered into as of
the  10th  day of  January,  1996,  by and  between  EDITEK,  INC.,  a  Delaware
corporation  ("Purchaser"),  MEDTOX LABORATORIES,  INC., a Minnesota corporation
("Seller"), and PSYCHIATRIC DIAGNOSTIC LABORATORIES OF AMERICA, INC., a Delaware
corporation ("Assignee").

         WHEREAS,  Seller  and  Purchaser  are  parties  to that  certain  Asset
Purchase  Agreement  dated  as of July  1,  1995,  and  that  certain  Amendment
Agreement  dated as of January 2, 1996,  pursuant to which  Purchaser  agreed to
purchase  and Seller  agreed to sell  substantially  all of the assets of Seller
(collectively, the "Purchase Agreement"); and

         WHEREAS,  Purchaser desires to assign to Assignee,  Assignee has agreed
to assume and Seller desires to consent to the assignment of, Purchaser's rights
under the Purchase  Agreement  under the terms and  conditions set forth herein;
and

         WHEREAS,  Assignee  is an  Affiliate  of  Purchaser  (as  such  term is
contemplated in the Purchase Agreement) of Purchaser; and

         WHEREAS, the assignment effected hereby is permitted under Section 13.3
of the Purchase Agreement.

         NOW, THEREFORE,  in consideration of the foregoing premises,  and other
good and  valuable  consideration,  the receipt and adequacy of which are hereby
acknowledged, the parties hereto agree as follows:

         1.  Assignment.  Purchaser  hereby  assigns and  transfers to Assignee,
Purchaser's  rights to purchase  assets  pursuant  to the terms of the  Purchase
Agreement.

         2.  Acceptance of Assignment.  Assignee hereby accepts the rights being
assigned hereby and assumes all responsibilities and obligations of Purchaser as
set forth in the Purchase  Agreement.  Assignee  hereby  covenants and agrees to
perform all terms and conditions contained in the Purchase Agreement.

         3.  Non-Release  of  Purchaser.  In accordance  with the  provisions of
Section 13.3 of the Purchase Agreement,  Purchaser agrees that the assignment to
Assignee of its rights under the Purchase Agreement shall not operate to release
Purchaser  from any  liability  to Seller  under  the  Purchase  Agreement,  and
Purchaser  shall remain  obligated to perform all terms and conditions and shall
remain  liable for all  indemnification  obligations  contained  in the Purchase
Agreement required to be performed by Purchaser.







         4. Seller's Consent. Seller hereby consents to the foregoing assignment
on the terms and  conditions  set forth  herein,  and in  connection  therewith,
agrees to treat  Assignee  for all  purposes  as  Purchaser  under the  Purchase
Agreement  and to take  whatever  action may be necessary  to transfer  Seller's
assets to  Assignee,  including  without  limitation,  executing  or causing the
execution of deeds,  assignments,  consents and other  similar  documents in the
name of Assignee.

         5. Additional  Party. By execution of this  Assignment,  Assignee shall
become a party to the  Purchase  Agreement  and shall  hereafter be bound by the
terms and conditions thereof.

         6.  Warranties  of  Purchaser.  Purchaser  warrants and  represents  to
Assignee as follows: (a) the Purchase Agreement is in full force and effect; (b)
neither  the  Purchase  Agreement  nor  any  of  the  obligations,   duties  and
responsibilities  of the  Purchaser  or Seller  thereunder  have  been  amended,
modified  or altered in any manner  other  than as  reflected  in the  Amendment
Agreement;  and (c) there  exists no  circumstance,  condition or act of default
which would entitle or permit  Seller to terminate the Purchase  Agreement or to
abridge any rights of Purchaser thereunder or exercise any remedies for default.

         7. Binding Effect. This Assignment shall be binding upon successors and
assigns of the parties.  The parties  shall execute and deliver such further and
additional  instruments,  agreements and other  documents as may be necessary to
evidence or carry out the provisions of this Assignment.

         8.  Counterparts.  This  Assignment  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.

         9. Governing Law; Interpretation. The execution and performance of this
Assignment  shall be governed by the substantive laws of the State of Minnesota,
without  giving effect to the provisions  thereof  relating to conflicts of law.
Unless otherwise defined herein, capitalized terms shall have the meanings given
to them under the Purchase Agreement.

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         IN WITNESS  WHEREOF,  the parties hereto have executed this  Assignment
effective as of the day and year first above written.

                               PURCHASER:

                              EDITEK, INC.


ATTEST:                                 By: _______________________________
                                        Title: ____________________________
[SEAL]


- ----------------------
  Secretary

                                 SELLER:

                                        MEDTOX LABORATORIES, INC.


ATTEST:                                 By: _______________________________
                                        Title: ____________________________
[SEAL]


- ----------------------
  Secretary

                                ASSIGNEE:

                                        PSYCHIATRIC DIAGNOSTIC LABORATORIES OF
                                          AMERICA, INC.


ATTEST:                                 By: _______________________________
                                        Title: ____________________________
[SEAL]


- ---------------------
  Secretary