Exhibit 10.39
                                                                   -------------
                             
                             AMENDMENT TO AGREEMENT

     Amendment  dated as of  April  30,  1997 to the  Agreement  made  effective
February 27, 1997 (the "Employment  Agreement") between DIANON Systems,  Inc., a
Connecticut  Corporation (the "Company"),  and Richard A. Sandberg,  residing at
233 Brushy Ridge, New Canaan, Connecticut ("Richard A. Sandberg").

     WHEREAS, the Company and Richard A. Sandberg desire to amend the Employment
Agreement.

     NOW, THEREFORE,  in consideration of the mutual covenants contained in this
Amendment, the Company and Richard A. Sandberg hereby agree as follows:

     1. Section 2 of the Employment  Agreement is hereby amended by deleting the
third  sentence  thereof  so  that as so  amended  Section  2 shall  read in its
entirety as follows:

               "2. STOCK OPTIONS

               All options to buy Company  stock held by Richard A.  Sandberg as
     of February 22, 1997,  ("Options") to the extent not previously vested will
     vest in full effective February 27, 1997, provided that Richard A. Sandberg
     does not revoke this Agreement pursuant to Section 24 of this Agreement.  A
     revocation by Richard A. Sandberg of this Agreement  pursuant to Section 24
     of this Agreement shall not affect (i) any Option (or portion thereof) that
     was not vested  pursuant  to this  Section 2 and (ii) any  Option  that was
     exercised  or  sold  by  Richard  A.  Sandberg  prior  to the  date of such
     revocation.  The options  will  otherwise be  exercisable  according to the
     terms of their initial grant(s)."

     2. The  Employment  Agreement is hereby  amended by adding a new Section 27
entitled "Secured Loan" which shall read in its entirety as follows:

               "27. SECURED LOAN

               Immediately  upon  execution  hereof,  the Company  shall loan to
     Richard A. Sandberg  Three Hundred  Thousand  Dollars  ($300,000.00)  ("the
     Loan") and in exchange  therefore  Richard A.  Sandberg  shall  execute and
     deliver to the Company  the  Secured  Promissory  Note  attached  hereto as
     Exhibit A and the Security  Agreement  attached hereto as Exhibit B. As set
     forth in the Secured  Promissory  Note, the Loan shall be repayable in full
     in two years and shall bear interest at the rate of 9.5% per annum, payable
     annually,  and shall be secured by the Options,  the shares of stock of the
     Company issuable upon exercise of the Options and 30,000 shares of stock of
     Milkhaus Laboratory, Inc. ("Milkhaus") owned by Richard A. Sandberg. As set
     forth in the Security  Agreement,  Richard A. Sandberg shall have the right





     to  exercise  the  Options  and to sell from time to time any or all of the
     shares of the Company or Milkhaus  held as  collateral  under the  Security
     Agreement  provided  that 60% of the gain  realized by Richard A.  Sandberg
     from any such sale is paid to the  Company  in  satisfaction  of Richard A.
     Sandberg's obligations under the Secured Promissory Note."

     3. Except as amended  hereby,  the Employment  Agreement  shall continue in
full force and effect in accordance with its terms.

                                                  DIANON SYSTEMS, INC.

                                                  By /S/  KEVIN JOHNSON
                                                     ------------------
                                                     Kevin Johnson


                                                  /S/  RICHARD A. SANDBERG
                                                  ------------------------
                                                  Richard A. Sandberg