Document:

EXHIBIT 10.21

                               SEVERANCE AGREEMENT

     THIS SEVERANCE  AGREEMENT dated as of December 1, 1999, is between Isolyser
Company,  Inc., a Georgia  corporation  (the  "Company"),  and Peter Schmitt,  a
Georgia resident ("Employee").

                                    RECITALS:

     R1. The Company and Employee entered into that certain Employment Agreement
(the  "Employment  Agreement")  bearing an effective  date of March 12, 1998, in
accordance with which the Company employed Employee.

     R2. With due regard to the recent divestitures completed by the Company and
other  factors  considered,  Employee  desires to resign and Company  desires to
accept the  resignation of Employee upon and subject to the terms and conditions
of this Severance Agreement.

     NOW,  THEREFORE,  for good and valuable  consideration  and intending to be
legally bound,  the parties agree as follows:

     1.  Resignation.  Employee  hereby  resigns as an  employee  of the Company
effective  February  1, 2000 (the  "Effective  Date"),  and the  Company  hereby
accepts such  resignation.  Such  resignation is by mutual agreement and not for
"Cause" or "Good Reason" as defined in the Employment Agreement.

     2. Severance. In consideration of Employee's release set forth in Section 4
below,  and the other covenants and undertakings  herein,  the Company agrees to
make a  severance  payment  to  Employee  of  $162,500  promptly  following  the
Effective Date of Employee's  resignation.  Such payment shall be reduced by all
applicable federal and state withholding obligations.  The Company shall pay the
cost of medical and dental COBRA coverages for the continued benefit of Employee
and his dependents for a period  terminating on the earlier of (a) twelve months
after the Effective Date of Employee's  resignation or (b) the commencement date
of  equivalent  benefits  from a new  employer,  provided  Employee's  continued
participation  is possible  under the general terms and provisions of such plan.
Employee shall not be entitled to any consulting fees set forth in Section 12 of
the Employment  Agreement until following the first anniversary of the Effective
Date of  Employee's  resignation.

     3. Stock  Options.  Employee  holds the stock options issued by the Company
identified on Exhibit A attached  hereto and  incorporated  herein by reference.
Provided  Employee's  employment shall not have been terminated for Cause as set
forth in the  Employment  Agreement  prior to the  Effective  Date of Employee's
resignation,  (a) all of  Employee's  stock  options  shall become vested on the
Effective Date of Employee's  resignation,  and (b) the expiration of Employee's
stock options  shall occur on the second  anniversary  of the Effective  Date of
Employee's resignation rather than three months following Employee's termination
of employment with the Company,  such resignation  being deemed a retirement for
purposes of the Company's Stock Option Plan.

<PAGE>

     4. Release.  In  consideration  of the covenants of the Company in favor of
the  Employee  as set  forth  in  this  Severance  Agreement,  the  receipt  and
sufficiency of which is hereby acknowledged, Employee, on behalf of himself, his
heirs,  executors,  administrators,  successors and assigns, hereby releases and
forever  discharges  the Company  and each of its  present and former  officers,
directors,   employees,  agents,  attorneys,  insurers,   affiliates,   parents,
subsidiaries and representatives (collectively, the "Released Parties") from any
and all  claims  (including  but not  limited  to costs and  attorneys  fees) of
whatever  kind or nature,  joint or several,  under any federal,  state or local
statute, ordinance or under the common law, including, but not limited to, Title
VII of the Civil  Rights  Act of 1964,  the Civil  Rights  Act of 1991,  the Age
Discrimination in Employment Act of 1967, the Older Workers' Benefit  Protection
Act, and any other  employment  discrimination  law, as well as any other claims
based on the constitutional,  statutory,  common law or regulatory grounds, that
he has now or may have in the future against the Released Parties, whether known
or unknown,  which are based on acts or omissions  arising or occurring prior to
the  date of this  Severance  Agreement.  Notwithstanding  the  foregoing,  that
certain  Indemnity  Agreement  effective  as of  May  8,  1997  (the  "Indemnity
Agreement"),  between the Company and  Employee  shall  remain in full force and
effect in accordance with its terms.

     5. Ratification. Except as affected hereby, the terms and provisions of the
Employment  Agreement are hereby ratified and confirmed by Employee,  including,
without  limitation,  the  protective  covenants  set forth in  Section 9 of the
Employment Agreement, which shall remain in full force and effect.

     6.  Cancellation of Agreement.  The Company may at its election upon notice
to  the  Employee  terminate  this  Severance  Agreement  in  the  event  of any
termination of Employee's employment for Cause in accordance with the Employment
Agreement prior to the Effective Date of Employee's resignation,  in which event
this Severance  Agreement  shall be of no further force or affect.  The Employee
may in his sole  and  absolute  discretion  elect to  terminate  this  Severance
Agreement  and elect  not to  resign  his  employment  at any time  prior to the
Effective Date of his resignation by notice to the Company,  in which event this
Severance  Agreement  shall be of no further  force or effect.

     7.  Outplacement.  Services.  To the extent requested by Employee,  Company
shall  provide to Employee  through  Wright and  Associates up to four months of
outplacement  services  following the Effective  Date of Employee's  resignation
hereunder.

     8.  Miscellaneous.  This  Severance  Agreement  may be executed in multiple
counterparts,  each of which shall be deemed an original.  All payments made and
benefits provided to Employee under this Severance Agreement shall be net of any
tax required to be withheld by the Company under  applicable law. This Severance
Agreement shall be governed in accordance with the laws of the State of Georgia.
This Severance Agreement and all of the terms,  provisions and conditions hereof
shall  be  binding  upon and  inure  to the  benefit  of be  enforceable  by the
successors,  heirs and  personal  representatives  of Employee  and the Company.
Nothing contained herein shall restrict, alter or amend the Indemnity Agreement.
Any notices  required  or  permitted  by this  Severance  Agreement  shall be in
writing delivered, in the case of the Company, to the attention of the President
of the Company and, in the case of the Employee,  to the  Employee's  last known
residence address as set forth on the books and records of the Company.

                                      2
<PAGE>

     IN WITNESS WHEREOF,  the parties have caused this Severance Agreement to be
executed and delivered as of the date first above written.

                                             ISOLYSER COMPANY, INC.

                                             By:________________________________
                                             Title:_____________________________

                                             ___________________________________
                                             Peter SchmittEXHIBIT 10.52

                               AMENDMENT AGREEMENT

      This is an Agreement dated as of December 23, 1999 (the "Agreement") by
and among DIANON SYSTEMS, INC. ("DIANON"), on the one hand, and A. Bruce Shapiro
("A. Shapiro"), Ralph M. Richart, M.D. ("Richart"), Dana Shapiro ("D. Shapiro"),
Kyto Meridien Diagnostics, L.L.C. ("KMD"), Kyto Diagnostics L.P. ("Kyto") and
Meridien Diagnostics Labs, Inc. ("Meridien"), on the other hand.

                                   WITNESSETH:

      WHEREAS, KMD, Kyto, Meridien, A. Shapiro and Richart (collectively the
"Sellers") entered into an Asset Purchase Agreement dated as of April 7, 1999
(the "Asset Agreement") with DIANON for the purchase of substantially all of the
assets of KMD; and

      WHEREAS, pursuant to the Asset Agreement, A. Shapiro entered into a
Consulting Agreement with DIANON dated as of May 1, 1999 (the "Consulting
Agreement"); and

      WHEREAS, pursuant to the Asset Agreement, Richart entered into an
Employment Agreement with DIANON dated as of May 1, 1999 (the "Employment
Agreement"); and

      WHEREAS, pursuant to the Asset Agreement, D. Shapiro entered into an
Employment Agreement with DIANON dated as of May 1, 1999; and

      WHEREAS, Section 3(a) of the Asset Purchase Agreement requires DIANON to
make certain payments to KMD for Purchased Receivables; and

      WHEREAS, certain disputes have arisen concerning the Employment and
Consulting Agreements.

      NOW, THEREFORE, in consideration of the foregoing premises and the mutual
covenants and agreements contained herein, the parties hereto, intending to be
legally bound, hereby agree as follows:

1.    OFFSETTING PAYMENTS.

      (A) In full and complete satisfaction of its obligation to pay for the
Purchased Receivables under Section 3(a) of the Asset Agreement, DIANON shall
pay to KMD three hundred ninety-nine thousand eight hundred and sixty-two
($399,862) dollars in the manner described in paragraph (C) below.

      (B) In the manner described in paragraph (C) below, A. Shapiro, Richart
and D. Shapiro shall refund the amounts indicated below that were paid to them
under their respective Consulting and Employment Agreements through December 31,
1999:

      A. Shapiro:   One hundred fifty-four thousand five hundred fifty-two
                    ($154,552) dollars;

      Richart:      One hundred thirty-five thousand three hundred twenty-one
                    ($135,321) dollars;

      D. Shapiro:   Forty-three thousand five hundred fifty-seven ($43,557)
                    dollars

      (C) The payments under paragraph (A) and (B) above shall be made by
offsetting the amounts to be paid by A. Shapiro, Richart and D. Shapiro against
the payments to be made by DIANON. The payments required by each of A. Shapiro,
Richart, D. Shapiro and DIANON shall be recognized to

                                      E-1
<PAGE>

have been paid in full upon the payment by DIANON to KMD of the net balance
resulting from the offsetting payments, which net balance is sixty-six thousand
four hundred thirty-two ($66,432) dollars.

2.    AMENDMENT TO AGREEMENTS.

      (A) The term specified in Section 3 of the Consulting Agreement is hereby
amended to end on the second anniversary of the Closing Date of the Asset
Agreement.

      (B) The term specified in Section 3 of the Employment Agreement is hereby
amended to end on the second anniversary of the Closing Date of the Asset
Agreement.

      (C) Except as amended herein, the Consulting Agreement and Employment
Agreement shall remain in full force and effect in accordance with their terms
and may not be further amended except in a writing signed by the parties
thereto. In particular, the term and requirements of the restrictive covenants
set forth in Section 5 of the Consulting Agreement and Section 5 of the
Employment Agreement shall remain as set forth in those agreements and are not
altered or diminished in any respect as a consequence of these amendments.

3.    CROSS-RELEASES.

      Simultaneously with the execution of this Agreement, DIANON shall execute
a release in the form of Exhibit A annexed hereto and Sellers shall execute a
release in the form of Exhibit B annexed hereto.

4.    NON ADMISSION.

      Nothing in this Agreement shall be construed as, and none of the Parties
hereto has made, an admission of liability or wrongdoing.

5.    COUNTERPARTS.

      This Agreement and the Releases may be signed in counterparts, each of
which when so executed and delivered shall be deemed an original.

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<PAGE>

6.    NON-DEFAMATION

      No person within the senior management of DIANON shall make any defamatory
or misleading statement that is calculated to have the effect or purpose of
maligning the integrity, management, products or services of the Sellers or
their officers, directors, shareholders or principals, including D. Shapiro,
whether in connection with the Asset Purchase, Employment or Consulting
Agreements or otherwise.

7.    REPRESENTATION AND WARRANTY

      DIANON represents and warrants to the Sellers that, as of the date of this
Agreement, other than issues raised in discussions or correspondence between
DIANON and any of the Sellers or D. Shapiro, including without limitation issues
relating to the Oxford contract, potential professional liability claims, which
matters are released pursuant to this Agreement, and matters disclosed by
Sellers pursuant to the Asset Agreement, DIANON, other than members of DIANON to
whom this representation is being made, has no knowledge of any facts or any
threatened or pending claims by any third party that would form the basis of any
additional claim, cause of action or judgment against the Sellers or D. Shapiro.

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

DIANON SYSTEMS, INC.

                                               /s/ A. Bruce Shapiro
                                               ---------------------------------
                                               A. Bruce Shapiro
/s/ KCJ
-----------------------------------------
By:  Kevin Johnson                             /s/ Ralph Richart
                                               ---------------------------------
                                               Ralph M. Richart, M.D.

KYTO MERIDIEN DIAGNOSTICS, L.L.C.              /s/ Dana Shapiro
                                               ---------------------------------
                                               Dana Shapiro

/s/ Ralph Richart
-----------------------------------------
By:  Bruce Shapiro or Ralph Richart, M.D.

MERIDIEN DIAGNOSTICS LABS, INC.                KYTO DIAGNOSTICS

/s/ Bruce Shapiro                              /s/ Ralph Richart
-----------------------------------------      ---------------------------------
By:  Bruce Shapiro                             By: Ralph Richart, M.D.

                                      E-3
<PAGE>

                        EXHIBIT A TO AMENDMENT AGREEMENT

                                     RELEASE

            TO ALL TO WHOM THESE PRESENTS SHALL COME OR MAY CONCERN, KNOW THAT
Dianon Systems, Inc. a corporation organized and existing under the laws of the
State of Delaware, (the "RELEASOR"), in consideration of the sum of $1.00 and
other good and valuable consideration, receipt of which is hereby acknowledged,
except as limited herein, releases, discharges and acquits forever Kyto Meridien
Diagnostics, L.L.C., a New York limited liability company, Meridien Diagnostics
Labs, Inc., a New York corporation, Kyto Diagnostics, L.P. a New York limited
partnership, A. Bruce Shapiro, Ralph M. Richart, M.D., and Dana Shapiro (the
"RELEASEES"), RELEASEES' heirs, executors, administrators, members, partners,
officers, employees, agents, successors and assigns, from all actions, causes of
action, suits, debts, dues, sums of money, accounts, reckonings, bonds, bills,
specialties, covenants, contracts, controversies, agreements, promises,
variances, trespasses, damages, judgments, extents, executions, claims and
demands whatsoever in law, admiralty or equity, which the RELEASOR and the
RELEASOR's heirs, executors, administrators, partners, officers, directors,
shareholders, employees, agents, successors and assigns ever had, now have or
hereafter can, shall or may have, for, upon or by reason of any breach of
representation and warranty by RELEASEES concerning revenues derived from a
contract to service Oxford Health Plans and any financial consequences to the
business of RELEASOR from the beginning of the world to the date of this Release
arising from any matter, cause or thing known by DIANON, other than employees
and consultants of DIANON who are subject to this Release.

1. Nothing in this Release is intended to, nor shall, release or waive any right
or obligation of the parties hereto arising under a certain Amendment Agreement
dated as of December 23, 1999 and executed by the parties in connection with
this Release, or the Employment and Consulting Agreements referred to therein.

2. Nothing in this Release is intended to, nor shall, release or waive any
action, causes of action, suits, debts, dues, sums of money, accounts,
reckonings, bills, specialties, covenants, contracts, controversies, agreements,
promises, damages, judgments, claims or demands whatsoever, in law or in equity,
which RELEASOR had, now has or hereafter can, shall or may have against
RELEASEES, or any RELEASEE, or any of RELEASEES' heirs, executors,
administrators, members, partners, officers, employees, agents, successors or
assigns, with respect to any governmental or third party claim, proceeding,
investigation, suit, controversy, judgment or action, whether s based on known
facts or facts unknown as of the date of this Release.

                                      E-4
<PAGE>

3. The signatory to this Release hereby warrants and represents that he is duly
authorized to enter into this Release on behalf of the persons and entities on
whose behalf he purports to act.

4. This Release shall in all respects be interpreted, enforced and governed
under the laws of the State of New York without regard to New York's conflicts
of laws principles.

5. Whenever text hereof requires, the use of the singular number shall include
the appropriate plural number.

6. This Release may not be changed orally.

            IN WITNESS WHEREOF, this Release has been executed by a duly
authorized representative as of the date set forth below.

                                    DIANON SYSTEMS, INC.

                                     By:     /s/ KCJ
                                             ---------------------------------
                                     Title:  President and CEO
                                             ---------------------------------
                                     Date:   1/26/00
                                             ---------------------------------

                                ACKNOWLEDGMENT

STATE  OF CONNECTICUT   )
                        )  SS.:
COUNTY OF FAIRFIELD     )

            On the 26th day of January, 2000, before me personally came Kevin C.
Johnson, to me known, who by me duly sworn, did depose and say that deponent
resides at Keelers Ridge, Wilton, Ct, that deponent is a duly authorized officer
of Dianon Systems, Inc. the corporation described herein as Releasor and which
executed the foregoing Release, and that deponent signed deponent's name thereto
by authority of the board of directors of said corporation.

                                            Merrilee B. Tooker
                                            ------------------
                                              Notary Public

                                      E-5
<PAGE>

                        EXHIBIT B TO AMENDMENT AGREEMENT

                                     RELEASE

            TO ALL TO WHOM THESE PRESENTS SHALL COME OR MAY CONCERN, KNOW THAT
A. Bruce Shapiro, Ralph M. Richart, M.D., Dana Shapiro, Kyto Meridien
Diagnostics, L.L.C., Kyto Diagnostics, L.P. and Meridien Diagnostics Labs, Inc.
(the "RELEASORS"), in consideration of the sum of $1.00 and other good and
valuable consideration, receipt of which is hereby acknowledged, release,
discharge and acquit forever Dianon Systems, Inc., a Delaware Corporation (the
"RELEASEE"), RELEASEE's heirs, executors, administrators, members, partners,
officers, employees, agents, successors and assigns, from all known actions,
causes of action, suits, debts, dues, sums of money, accounts, reckonings,
bonds, bills, specialties, covenants, contracts, controversies, agreements,
promises, variances, trespasses, damages, judgments, extents, executions, claims
and demands whatsoever, in law, admiralty or equity, which the RELEASORS and the
RELEASORS's heirs, executors, administrators, partners, officers, directors,
shareholders, employees, agents, successors and assigns ever had, now have or
hereafter can, shall or may have, for, upon or by reason of RELEASEE's payment
obligations for Purchased Receivables under Section 3 (A) of the Asset Purchase
Agreement by and among Dianon Systems, Inc., Kyto Meridien Diagnostics, L.L.C.
et alia dated April 7, 1999.

            1. Nothing in this Release is intended to, nor shall, release or
waive any right or obligation of the parties hereto arising under a certain
Amendment Agreement dated as of December 23, 1999 and executed by the parties in
connection with this Release, or the Employment and Consulting Agreements
referred to therein.

            2. The signatories to this Release hereby warrant and represent that
he or she is duly authorized to enter into this Release on behalf of the persons
and entities on whose behalf he or she purports to act.

            3. This Release shall in all respects be interpreted, enforced and
governed under the laws of the State of New York without regard to New York's
conflicts of laws principles.

            4. Whenever text hereof requires, the use of the singular number
shall include the appropriate plural number.

            5. This Release may not be changed orally.

                                      E-6
<PAGE>

            IN WITNESS WHEREOF, this Release has been executed by a duly
authorized representative as of the date set forth below.

                                                 /s/ A. Bruce Shapiro
                                               ---------------------------------
KYTO MERIDIEN DIAGNOSTICS, L.L.C.              A. Bruce Shapiro

/s/ Ralph Richart                              /s/ Ralph Richart
                                               ---------------------------------
-----------------------------------------
By:  Bruce Shapiro or Ralph Richart,           Ralph M. Richart, M.D.
M.D.

                                               /s/ Dana Shapiro

                                               ---------------------------------
                                               Dana Shapiro

MERIDIEN DIAGNOSTICS LABS, INC.

                                               KYTO DIAGNOSTICS, L.P.
/s/ A. Bruce Shapiro

-----------------------------------------
By:  Bruce Shapiro                             /s/ Ralph Richart
                                               ---------------------------------
                                               By:  Ralph Richart, M.D.

                                      E-7
<PAGE>

                                ACKNOWLEDGMENT

STATE OF NEW YORK   )
                    ) SS.:
COUNTY OF NEW YORK  )

            On the 27th day of January, 2000, before me personally came Ralph
Richart to me known, who by me duly sworn, did depose and say that deponent
resides at Oakdale, NY, that deponent is a duly authorized officer of Kyto
Meridien Diagnostics, L.L.C.. the corporation described herein as Releasor and
which executed the foregoing Release, and that deponent signed deponent's name
thereto by authority of the board of directors of said corporation.

                                            Catherine McGrath
                                            -----------------
                                              Notary Public

                                 ACKNOWLEDGMENT

STATE OF NEW YORK   )
                    ) SS.:
COUNTY OF NEW YORK  )

            On the 27th day of January, 2000, before me personally came Bruce
Shapiro, to me known, who by me duly sworn, did depose and say that deponent
resides at Woodbury, NY, that deponent is a duly authorized officer of Meridien
Diagnositcs Labs, Inc.. the corporation described herein as Releasor and which
executed the foregoing Release, and that deponent signed deponent's name thereto
by authority of the board of directors of said corporation.

                                          Lindsay Mara Schoen
                                          -------------------
                                          Notary Public

                                      E-8
<PAGE>

                                 ACKNOWLEDGMENT

STATE OF NEW YORK       )
                        ) SS.:
COUNTY OF NASSAU        )

            On the 26th day of January, 2000, before me personally came Dana
Shapiro, to me known, who by me duly sworn, did depose and say that deponent
resides at Woodbury, NY, that deponent described herein as Releasor and which
executed the foregoing Release.

                                               Kathleen Andres
                                               ---------------
                                                Notary Public

                                 ACKNOWLEDGMENT

STATE OF NEW YORK       )
                        ) SS.:
COUNTY OF NASSAU        )

            On the 26th day of January, 2000, before me personally came A. Bruce
Shapiro, to me known, who by me duly sworn, did depose and say that deponent
resides at Woodbury, NY, that deponent is the person described herein as
Releasor and who executed the foregoing Release.

                                              Kathleen Andres
                                              ---------------
                                               Notary Public

                                      E-9
<PAGE>

                                 ACKNOWLEDGMENT

STATE OF NEW YORK       )
                        ) SS.:
COUNTY OF NEW YORK      )

            On the 27th day of January, 2000, before me personally came Ralph M.
Richart, M.D., to me known, who by me duly sworn, did depose and say that
deponent resides at Oakdale, NY, that deponent is the person described herein as
Releasor and who executed the foregoing Release.

                                            Catherine McGrath
                                            -----------------
                                              Notary Public

                                      E-10

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