EXHIBIT 10.25

                           SECOND AMENDMENT AGREEMENT

AGREEMENT (the  "Agreement")  dated as of January 30, 1996 between EDITEK,  Inc.
("EDITEK"),  Psychiatric  Diagnostic  Laboratories  of America,  Inc.  ("PSDLA")
(collectively, "Purchaser") and MedTox Laboratories, Inc. ("Seller").

                                   WITNESSETH:

WHEREAS,  Seller and Purchaser are parties to a certain Asset Purchase Agreement
dated as of July 1, 1995, which has been amended by an Amendment Agreement dated
as of January 2, 1996 between Seller and EDITEK ("Amendment  Agreement"),  which
agreement  was  assigned  by  EDITEK  to  PSDLA  (collectively,   the  "Purchase
Agreement"),  and Seller and Purchaser desire to amend the Purchase Agreement to
define the specific time of Closing of the transactions contemplated therein and
to revise the method for  calculating  the market  price of the Common Stock for
certain purposes therein.

NOW, THEREFORE,  in consideration of the premises and the mutual promises of the
parties set forth below, the parties hereby agree as follows:

1. The Purchase  Agreement is hereby amended so that (i) the Closing Date Market
Price,  as defined in Section  3.2 (b) of the  Amendment  Agreement  and for all
purposes therein, is changed to read as follows:

     (b) "Closing Date Market Price" shall mean $2.838,  which number represents
the average of the daily closing  sales  prices,  as reported in The Wall Street
Journal,  of the Common Stock, for the five Trading Days  immediately  preceding
January 25, 1996.

     and (ii) the Repricing Date Market Price,  as defined in Section 3.2 (j) of
the  Amendment  Agreement  and for all purposes  therein,  is changed to read as
follows:

                  (j)  "Repricing  Date Market  Price" shall mean the average on
the Repricing Date and the four Trading Days preceding the Repricing Date of the
daily  closing  sales  prices,  as reported in The Wall Street  Journal,  of the
Common Stock.

2. The Closing of the transactions  contemplated in the Purchase Agreement shall
be deemed to occur at the close of business on January 30, 1996, notwithstanding
that the actual  Closing  occurred at some other hour of the day on such Closing
Date.

3. The assets and  liabilities  being  transferred  by Seller are the assets and
liabilities  of Seller as of January 30,  1996,  all as required by the Purchase
Agreement.  Notwithstanding  the foregoing,  the parties desire to give economic
effect to the  transaction  as of the close of business on January 26, 1996 and,



accordingly desire to allocate  responsibility  for payroll,  trade payables and
collections by agreeing as follows:

         (a) Purchaser shall pay the amount of any payroll and related  expenses
for employees and  consultants of Seller for the period  commencing  January 20,
1996  through  the close of  business  on January  30,  1996,  but Seller  shall
immediately  reimburse  Purchaser  for such payments for the period from January
20, 1996 through the close of business on January 26, 1996;

     (b) Seller shall pay Purchaser an amount equal to the amounts  collected by
Seller after the close of business on January 26, 1996; and

         (c)  Purchaser  shall assume and have  responsibility  to pay all trade
payables of Seller that were  incurred  consistent  with  Sellers' past practice
disclosed to  Purchaser  and which  remained  unpaid at the close of business on
January 30, 1996,  provided that past practice  disclosed to Purchaser would not
have required payment prior to the close of business on January 26, 1996.

         Notwithstanding  the foregoing,  Purchaser  shall have no liability for
tort or similar  liabilities  of Seller that arise out of acts or omissions that
occurred prior to the close of business on January 30, 1996.

4.     All  representations  and  warranties  made by Seller and  Purchaser  in
Sections  5.2 and 6.2 of the  Purchase  Agreement  are hereby  extended  to this
Agreement and the transactions contemplated hereby.

5.     Except as set forth above, the Purchase Agreement shall remain unchanged
and in full force and effect.
       
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IN WITNESS WHEREOF, the parties have caused this Agreement to be signed by their
respective officers thereto duly authorized as of the date first written above.


                                      MEDTOX LABORATORIES, INC.


                                      By:________________________________
                                      Name: ___________________________
                                      Title:____________________________


                                      EDITEK, INC.
          
                                      By:_________________________________
                                      Name:____________________________
                                      Title:_____________________________


                                      PSYCHIATRIC DIAGNOSTIC
                                      LABORATORIES OF AMERICA, INC.

                                      By:_________________________________
                                      Name:____________________________
                                      Title:_____________________________