Exhibit 8.2

                    [Fulbright & Jaworski L.L.P. Letterhead]


August 3, 2001

UroCor, Inc.
840 Research Parkway
Oklahoma City, Oklahoma  73104


Ladies and Gentlemen:


                  You have requested our opinion concerning certain United
States federal income tax consequences of the merger (the "Merger") of UroCor
Acquisition Corp. ("Merger Sub"), a Delaware corporation and a direct
wholly-owned subsidiary of Dianon Systems, Inc., a Delaware corporation
("Parent"), with and into UroCor, Inc., a Delaware corporation ("Company"),
pursuant to the Agreement and Plan of Merger, dated as of June 28, 2001 (the
"Merger Agreement"), by and among Parent, Merger Sub, and Company. Unless
otherwise indicated, each capitalized term used herein has the meaning ascribed
to it in the Merger Agreement.

                  In connection with this opinion, we have examined and relied
upon (i) the Merger Agreement, (ii) the Joint Proxy Statement/Prospectus of
Parent and Company (the "Proxy Statement/Prospectus") included as part of the
Registration Statement on Form S-4 filed with the Securities and Exchange
Commission (the "Commission") under the Securities Act of 1933, as amended (the
"Securities Act"), and the Securities Exchange Act of 1934, as amended, (iii)
the representation letters dated the date hereof and delivered by Parent and
Company to us pursuant to Section 5.14 of the Merger Agreement, and (iv) such
other documents as we have deemed necessary or appropriate in order to enable us
to render the opinion below (all documents described in this sentence are
collectively referred to as the "Documents").

                  For purposes of this opinion, we have assumed (i) that the
Merger will be consummated in the manner described in the Merger Agreement and
the Proxy Statement/Prospectus, (ii) that the Documents are complete and
authentic and have been duly authorized, executed and delivered, (iii) that all
of the information, facts, statements, representations and covenants contained
in the Documents (without regard to any qualification stated therein and without
undertaking to verify such information, facts, statements, representations and
covenants by independent investigation) are true and accurate at all relevant
times (including as of the effective time of the Merger), (iv) that the
respective parties to the Documents and all parties referred to therein will act
in all respects and at all relevant times in conformity with the requirements
and provisions of the Documents, and (v) that none of the terms and conditions
contained in the Documents has been or will be waived or modified in any
respect. Any change in the accuracy or completeness of any of the information,
facts,



statements, representations, covenants, Documents or assumptions on which our
opinion is based could affect our conclusions.

                  The opinion expressed herein is based on the applicable
provisions of the Internal Revenue Code of 1986, as amended (the "Code"),
Treasury Department regulations promulgated thereunder, pertinent judicial
authorities, interpretive rulings of the Internal Revenue Service and such other
authorities as we have considered relevant, any of which may be changed at any
time (possibly with retroactive effect). Any change in the authorities on which
our opinion is based could affect our conclusions. We express no opinion other
than as to the United States federal income tax matters set forth below. Our
opinion does not address any non-income tax or any foreign, state or local tax
consequences of the Merger.

                  Based upon and subject to the foregoing, it is our opinion
          that:

                  1.   the Merger will be treated for United States federal
          income tax purposes as a reorganization within the meaning of Section
          368(a) of the Code; and

                  2.   Company, Parent and Merger Sub will each be a party to
          that reorganization within the meaning of Section 368(b) of the Code.

                  Our opinion is expressed as of the date hereof, and we are
under no obligation to supplement or revise our opinion to reflect any change
(including any change that has retroactive effect) (i) in applicable law, or
(ii) that causes any information, fact, statement, representation, covenant,
Document or assumption on which our opinion is based to become untrue or
incorrect.

                  This letter is furnished to you solely for use in connection
with the Merger, as described in the Merger Agreement and the Proxy
Statement/Prospectus, and is not to be used, circulated, quoted, or otherwise
referred to for any other purpose without our express written consent. In
accordance with the requirements of Item 601(b)(23) of Regulation S-K under the
Securities Act, we hereby consent to the discussion of this opinion in the Proxy
Statement/Prospectus, to the filing of this opinion as an exhibit to the Proxy
Statement/Prospectus, and to the reference to our firm under the headings "The
Merger--Material Federal Income Tax Consequences of the Merger" and "Certain
Legal Information--Legal Matters" in the Proxy Statement/Prospectus. In giving
such consent, we do not thereby admit that we are in the category of persons
whose consent is required under Section 7 of the Securities Act or the rules and
regulations of the Commission thereunder.

                                Very truly yours,


                                FULBRIGHT & JAWORSKI L.L.P.