EXHIBIT 10.41
                                                                   -------------

                             SECURED PROMISSORY NOTE


$300,000                                                 April 30, 1997



     FOR VALUE  RECEIVED,  Richard  A.  Sandberg  and his heirs,  executors  and
administrators  ("Borrower")  hereby  promises  to pay to DIANON  Systems,  Inc.
("Lender")  the principal sum of Three Hundred  Thousand  Dollars  ($300,000) on
April 30,  1999,  and to pay interest on the unpaid  principal  balance from the
date  hereof  until paid in full at the rate of 9.5% per annum on April 30, 1998
and April 30, 1999.

     Payments of principal and interest shall be made in lawful  currency of the
United  States at the  offices  of Lender at 200  Watson  Boulevard,  Stratford,
Connecticut or such other place as Lender may designate.

     This Note may be prepaid by Borrower prior to its stated  maturity in whole
or in  part at any  time  or from  time to  time,  without  penalty  or  premium
(together  with  interest  accrued  to the date of  prepayment  on the amount of
principal being prepaid).

     The obligations of Borrower under this Note are secured by a first priority
pledge of and security  interest in (i)  Borrower's  rights under his options to
purchase  Common  Stock of Lender,  (ii) any shares of stock of Lender  issuable
upon  exercise  of such  options  and (iii)  30,000  shares of stock of Milkhaus
Laboratory,  Inc. owned by Borrower,  pursuant to a Security Agreement dated the
date hereof  (the  "Security  Agreement").  Borrower  agrees  that the  Security
Agreement  shall be binding upon the Borrower and that the grant of the security
interest in the  Collateral  (as  defined in the  Security  Agreement)  shall be
irrevocable  and  unconditional,  irrespective  of  the  validity,  legality  or
enforceability   of  the  obligations  of  Borrower   hereunder  and  the  other
Obligations (as defined in the Security Agreement), the absence of any action to
enforce the same, any waiver or consent by the Secured Party with respect to any
provisions  thereof,  or any  action to  enforce  the same or any other  similar
circumstances.

     In the event that (A) Borrower,  pursuant to or within the meaning of Title
11, U.S. Code or any similar foreign, United States federal or state law for the
relief  of  debtors  ("Bankruptcy  Law"),  (i)  commences  a  voluntary  case or
proceeding,  (ii) consents to the entry of an order for relief against  Borrower
in an involuntary  case or proceeding,  (iii)  consents to the  appointment  for
Borrower of a receiver, trustee, assignee,  liquidator,  sequestrator or similar
official  under any  Bankruptcy  Law (a  "Custodian"),  or (iv)  makes a general
assignment  for the benefit of Borrower's  creditors or (B) a court of competent
jurisdiction  enters an order or decree under any Bankruptcy Law that (i) is for
relief against  Borrower in an involuntary  case or proceeding,  (ii) appoints a
Custodian for all or substantially all of Borrower's properties, or (iii) orders
the liquidation of all or  substantially  all of the assets of Borrower,  or (C)
Borrower is in default under the Security Agreement or (D) Borrower fails to pay




interest when due, then in any such case all unpaid principal of and interest on
this Note shall IPSO FACTO become and be immediately due and payable without any
declaration or other act on the part of Lender.

     Borrower  shall pay all of the costs and  expenses of Lender in  connection
with any action  taken by it to collect or enforce  this Note,  to exercise  its
rights under the Security  Agreement  referred to above or to protect its rights
with respect thereto including  reasonable  attorney's fees, whether or not suit
be instituted,  and Lender may, without  limitation,  take judgment for all such
amounts.

     Borrower  hereby submits to the  jurisdiction of the courts of the State of
Connecticut  and  the  Federal  courts  of the  United  States  of  America  for
Connecticut  in respect of any legal action or proceeding  relating to this Note
or the  enforcement  of any  judgment in respect of this Note.  Borrower  hereby
waives, and agrees not to assert as a defense in any action,  suit or proceeding
for the  interpretation  and/or  enforcement  of this Note that  Borrower is not
subject thereto,  that such action,  suit or proceeding may not be brought or is
not  maintainable  in said  courts,  that this Note may not be enforced in or by
said courts, that Borrower's  property is exempt or immune from execution,  that
the suit, action or proceeding is brought in an inconvenient  forum or that that
venue of the suit,  action or  proceeding  is  improper.  Borrower  agrees  that
service of process in any such  action,  suit or  proceeding  shall be deemed in
every  respect  effective  service of process upon him if mailed or delivered to
Richard A. Sandberg, 233 Brushy Ridge, New Canaan, Connecticut 06840.

     This Note shall be governed by and construed in accordance with the laws of
the State of Connecticut  applicable to instruments  made and to be performed in
Connecticut and cannot be changed orally.



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