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                                                                   Exhibit 10.21

                            DEBT REPAYMENT AGREEMENT


          THIS DEBT REPAYMENT AGREEMENT (this "Agreement") is entered into as of
the 12th day of April, 1999, by and between DTM Corporation, a Texas corporation
(the "Company"), and DTM Acquisition Company, L.P., a Texas limited partnership
("DTMAC").

                                   RECITALS:

          WHEREAS, DTMAC holds all right, title and interest in and to a
$909,273.63 receivable (the "Debt") owed by the Company;

          WHEREAS, the Company and DTMAC desire to formalize the terms and
conditions pursuant to which the Debt will be repaid to DTMAC by the Company
partially for cash and partially for shares of the Company's Common Stock, par
value $0.0002 per share (the "Common Stock"); and

          WHEREAS, DTM's Board of Directors, including each director not
affiliated with or with any interest in DTMAC or its affiliates, after due
consideration of all factors it deems relevant, has approved the terms of the
transactions hereunder as being fair and in the best interest of the Company's
shareholders.

                                   AGREEMENT:

          NOW, THEREFORE, in consideration of the foregoing, the representations
and warranties, mutual covenants and agreements hereinafter set forth and
certain other good and valuable consideration, the receipt and sufficiency of
which are hereby acknowledged, it is hereby agreed between the Company and DTMAC
as follows:


     1.  Repayment of the Debt.
         ---------------------

     Cash Repayment. Subject to the terms and conditions of this Agreement, the
Company shall deliver to DTMAC at the Closing repayment of $454,273.63 by check,
wire transfer or any combination thereof. Upon receipt of this repayment, DTMAC
agrees to execute the Release, in substantially the form attached hereto as
Exhibit A.
---------

     Issuance of Common Stock.  Subject to the terms and conditions of this
Agreement, DTMAC agrees to purchase at the Closing, and the Company agrees to
sell and issue to DTMAC at the Closing, 352,167 shares of the Common Stock.

     Closing.  The closing of the transactions contemplated hereby shall take
place at the offices of Brobeck, Phleger & Harrison LLP, 301 Congress Avenue,
Suite 1200, Austin, Texas at 10:00 a.m., on June 11, 1999, or at such other time
and place as the Company and DTMAC mutually agree orally or in writing (which
time and place are designated as the "Closing").  At the Closing the Company
shall deliver to DTMAC a certificate representing the Common Stock that DTMAC is
purchasing against payment of the purchase price therefor by cancellation of
indebtedness.  DTMAC shall execute an instrument of cancellation and release, in
substantially the form attached hereto as Exhibit A.
                                          ---------


     2.  Representations and Warranties of the Company. The Company hereby
         ---------------------------------------------
represents and warrants to DTMAC that:
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     Organization, Good Standing and Qualification.  The Company is a
corporation duly organized, validly existing and in good standing under the laws
of the State of Texas. The Company is duly qualified to transact business and is
in good standing in each jurisdiction in which the failure to so qualify would
have a material adverse effect on its business or properties.

     Authorization.  All corporate action on the part of the Company, its
officers, directors and shareholders necessary for the authorization, execution
and delivery of this Agreement and the Registration Rights Agreement, the
performance of all obligations of the Company under such agreements, and the
authorization, issuance (or reservation for issuance), sale and delivery of the
Common Stock being sold hereunder has been taken or will be taken prior to the
Closing, and this Agreement and the Registration Rights Agreement constitute
valid and legally binding obligations of the Company, enforceable in accordance
with their respective terms, except (i) as limited by applicable bankruptcy,
insolvency, reorganization, moratorium and other laws of general application
affecting enforcement of creditors' rights generally and (ii) as limited by laws
relating to the availability of specific performance, injunctive relief or other
equitable remedies.

     Valid Issuance of Common Stock.  The Common Stock that is being purchased
by DTMAC hereunder, when issued, sold and delivered in accordance with the terms
of this Agreement for the consideration expressed herein, will be validly
issued, fully paid and nonassessable, free of preemptive rights, and will be
free of restrictions on transfer other than restrictions on transfer under this
Agreement and under applicable state and federal securities laws.

     Offering.  Subject in part to the truth and accuracy of DTMAC's
representations set forth in Section 3 of this Agreement, the offer, sale and
issuance of the Common Stock as contemplated by this Agreement are exempt from
the registration requirements of the Act, and neither the Company nor any
authorized agent acting on its behalf will take any action hereafter that would
cause the loss of such exemption.

     Disclosure.  The Company has fully provided DTMAC with all the information
that it has requested for deciding whether to purchase the Common Stock and all
information that the Company believes is reasonably necessary to enable it to
make such decision. To the best of the Company's knowledge, neither this
Agreement nor any other written statements or certificates made or delivered in
connection herewith or therewith contains any untrue statement of a material
fact or omits to state a material fact necessary to make the statements herein
or therein not misleading.


     3.  Representations and Warranties of DTMAC.  DTMAC hereby represents and
         ---------------------------------------
         warrants that:

     Authorization.  DTMAC has full power and authority to enter into this
Agreement, the Release and the Registration Rights Agreement and such Agreements
constitute their respective valid and legally binding obligations of DTMAC,
enforceable in accordance with their respective terms.

     Purchase Entirely for Own Account.  This Agreement is made with DTMAC in
reliance upon its representation to the Company, which by DTMAC's execution of
this Agreement DTMAC hereby confirms, that the Common Stock to be received by
DTMAC will be acquired for investment for DTMAC's own account, not as a nominee
or agent, and not with a view to the resale or distribution of any part thereof,
and that DTMAC has no present intention of selling, granting any participation
in, or otherwise distributing the same. By executing this Agreement, DTMAC
further represents that it does not have any contract, undertaking, agreement or
arrangement with any person to sell, transfer or grant participations to such
person or to any third person, with respect to any of the Common Stock.

     Disclosure of Information.  DTMAC believes it has received all the
information it considers necessary or appropriate for deciding whether to
purchase the Common Stock. DTMAC further represents that it has had an
opportunity to ask questions and receive answers from the Company regarding the
terms and conditions of the offering of the Common Stock and the business,
properties, prospects and financial condition of the Company. The

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foregoing, however, does not limit or modify the representations and warranties
of the Company in Section 2 of this Agreement or the right of DTMAC to rely
thereon.

     Investment Experience.  DTMAC is, or has been, an investor in securities of
companies in the development stage and acknowledges that it is able to fend for
itself, can bear the economic risk of its investment, and has such knowledge and
experience in financial or business matters that it is capable of evaluating the
merits and risks of the investment in the Common Stock.

     Restricted Securities.  DTMAC understands that the shares of Common Stock
it is purchasing are characterized as "restricted securities" under the federal
securities laws inasmuch as they are being acquired from the Company in a
transaction not involving a public offering and that under such laws and
applicable regulations such securities may be resold without registration under
the Act only in certain limited circumstances. In this connection, DTMAC
represents that it is familiar with SEC Rule 144, as presently in effect, and
understands the resale limitations imposed thereby and by the Act.

          DTMAC is aware of the fact the sale of these securities in the State
of Texas may be made in reliance upon exemptions provided under the Securities
Act of Texas.

     Legend.  It is understood that the certificates evidencing the Common Stock
may bear the following legend:

          "THESE SECURITIES HAVE NOT BEEN REGISTERED UNDER THE SECURITIES ACT OF
          1933, AS AMENDED. THEY MAY NOT BE SOLD, OFFERED FOR SALE, PLEDGED OR
          HYPOTHECATED IN THE ABSENCE OF A REGISTRATION STATEMENT IN EFFECT WITH
          RESPECT TO THE SECURITIES UNDER SUCH ACT OR AN OPINION OF COUNSEL
          SATISFACTORY TO THE COMPANY THAT SUCH REGISTRATION IS NOT REQUIRED OR
          UNLESS SOLD PURSUANT TO RULE 144 OF SUCH ACT."

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     4.  Conditions of DTMAC's Obligations at Closing.  The obligations of DTMAC
under Subsection 1.1 of this Agreement are subject to the fulfillment on or
before the Closing of each of the following conditions:

     Representations and Warranties.  The representations and warranties of the
Company contained in Section 2 shall be true on and as of the Closing with the
same effect as though such representations and warranties had been made on and
as of the date of such Closing.

     Performance.  The Company shall have performed and complied with all
agreements, obligations and conditions contained in this Agreement that are
required to be performed or complied with by it on or before the Closing.

     Qualifications.  All authorizations, approvals, or permits, if any, of any
governmental authority or regulatory body of the United States or of any state
that are required in connection with the lawful issuance and sale of the Common
Stock pursuant to this Agreement shall be duly obtained and effective as of the
Closing.

     Registration Rights Agreement.  The Registration Rights Agreement, in
substantially the form attached hereto as Exhibit B, shall have been executed
                                          ---------
and delivered by the Company and DTMAC, and shall be in full force and effect.

     Working Capital Line of Credit.  The Company shall have obtained from a
bank a working capital line of credit in the amount of at least $2.0 million by
June 11, 1999.

          4.1  Filing of a Notification of Issuance of Additional Shares with
Nasdaq.  The Company shall have provided evidence of its filing of a
Notification of Issuance of Additional Shares with The Nasdaq Stock Market.


     5.  Conditions of the Company's Obligations at Closing.  The obligations of
         --------------------------------------------------
the Company to DTMAC under this Agreement are subject to the fulfillment on or
before the Closing of each of the following conditions:

     Representations and Warranties.  The representations and warranties of
DTMAC contained in section 3 shall be true on and as of the Closing with the
same effect as though such representations and warranties had been made on and
as of the Closing.

     Performance.  DTMAC shall have performed and complied with all agreements,
obligations and conditions contained in this Agreement that are required to be
performed or complied with by it on or before the Closing.

     Qualifications.  All authorizations, approvals, or permits, if any, of any
governmental authority or regulatory body of the United States or of any state
that are required in connection with the lawful issuance and sale of the Common
Stock pursuant to this Agreement shall be duly obtained and effective as of the
Closing.

     Delivery of Release.  DTMAC shall have delivered the Release attached
hereto as Exhibit A.
          ---------

     Registration Rights Agreement.  The Registration Rights Agreement, in
substantially the form attached hereto as Exhibit B, shall have been executed
                                          ---------
and delivered by the Company and DTMAC, and shall be in full force and effect.

     Working Capital Line of Credit.  The Company shall have obtained from a
bank a working capital line of credit in the amount of at least $2.0 million by
June 11, 1999.

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     6.  Miscellaneous.
         -------------

     Survival of Warranties.  The warranties, representations and covenants of
the Company and DTMAC contained in or made pursuant to this Agreement shall
survive the execution and delivery of this Agreement and the Closing for a
period of six months.

     Successors and Assigns.  Except as otherwise provided herein, the terms and
conditions of this Agreement shall inure to the benefit of and be binding upon
the respective successors and assigns of the parties (including transferees of
any Common Stock purchased hereunder). Nothing in this Agreement, express or
implied, is intended to confer upon any party other than the parties hereto or
their respective successors and assigns any rights, remedies, obligations, or
liabilities under or by reason of this Agreement, except as expressly provided
in this Agreement.

     Governing Law.  The construction, validity and interpretation of this
Agreement will be governed by the internal laws of the State of Texas without
giving effect to any choice of law or conflict of law provision or rule (whether
of the State of Texas or any other jurisdiction) that would cause the
application of the laws of any jurisdiction other than the State of Texas.

     Counterparts.  This Agreement may be executed in one or more counterparts,
each of which shall be deemed an original, but all of which together shall
constitute one and the same document.

     Headings.  The headings of this Agreement are for convenience only and do
not constitute a part of this Agreement.

     Notices.  All notices, requests, consents, and other communications under
this Agreement shall be in writing and shall be delivered personally or by
facsimile transmission or by overnight delivery service or mailed by first class
certified or registered U.S. mail, return receipt requested, postage prepaid:

          If to the Company, at DTM Corporation, 1611 Headway Circle, Building
2, Austin, Texas 78754, Attention:  John S. Murchison, III, President and Chief
Executive Officer (fax (512) 339-0634), or at such other address or addresses as
may have been furnished in writing by the Company to DTMAC, with a copy to
Brobeck, Phleger & Harrison LLP, 301 Congress Avenue, Suite 1200, Austin, Texas
78701, Attention: J. Matthew Lyons, Esq. (fax (512) 477-5813); and

          If to DTMAC, at DTM Acquisition Company, L.P., 221 West 6th Street,
Suite 1520, Austin, Texas 78701, Attention:  Anthony Mariotti (fax (512) 320-
8940), or at such other address or addresses as may have been furnished to the
Company in writing by DTMAC, with a copy to Locke Liddell & Sapp LLP, 100
Congress, Suite 300, Austin, Texas  78701, Attention:  Curtis R. Ashmos, Esq.
(fax (512) 305-4800).

          Notices provided in accordance with this Subsection 6.6 shall be
deemed delivered upon personal delivery or three business days after deposit in
the mail.

     Finder's Fee.  Each party represents that it neither is nor will be
obligated for any finder's fee or commission in connection with this
transaction. DTMAC agrees to indemnify and to hold harmless the Company from any
liability for any commission or compensation in the nature of a finder's fee
(and the costs and expenses of defending against such liability or asserted
liability) for which DTMAC or any of its officers, partners, employees, or
representatives is responsible. The Company agrees to indemnify and hold
harmless DTMAC from any liability for any commission or compensation in the
nature of a finder's fee (and the costs and expenses of defending against such
liability or asserted liability) for which the Company or any of its officers,
employees or representatives is responsible.

     Expenses.  Each of the Company and DTMAC shall bear their own expenses
incurred with respect to this Agreement and the transactions contemplated
hereby.

     Amendments and Waivers.  Any term of this Agreement may be amended and the
observance of any term of this Agreement may be waived (either generally or in a
particular instance and either retroactively or

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prospectively), only with the written consent of the Company and DTMAC. Any
amendment or waiver effected in accordance with this paragraph shall be binding
upon each holder of any securities purchased under this Agreement at the time
outstanding (including securities into which such securities are convertible),
each future holder of all such securities, and the Company.

     Severability.  The invalidity or unenforceability of any provision of this
Agreement shall not affect the validity or enforceability of any other provision
of this Agreement.

     Entire Agreement.  This Agreement and the documents referred to herein
constitute the entire agreement among the parties and no party shall be liable
or bound to any other party in any manner by any warranties, representations, or
covenants except as specifically set forth herein or therein.


                 [Remainder of page intentionally left blank.]

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<PAGE>

          IN WITNESS WHEREOF, the parties have executed this Debt Repayment
Agreement as of the date first above written.


                                             DTM CORPORATION


                                             By: s/s JOHN S. MURCHISON, III
                                                ---------------------------
                                                     John S. Murchison, III
                                                     President and Chief
                                                     Executive Officer



                                             DTM ACQUISITION COMPANY, L.P.

                                             BY:  PROACTIVE-DTM, L.P.

                                             BY:  PROACTIVE FINANCE GROUP, LLC


                                             By: s/s ANTHONY MARIOTTI
                                                ---------------------------
                                                     Anthony Mariotti
                                                     Managing Member

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