EXHIBIT 8.1

                [LETTERHEAD OF ALSTON & BIRD LLP APPEARS HERE]


                               November 7, 1997

National Data Corporation
National Data Corporation Plaza
Atlanta, Georgia 30329-2010

        Re:  Agreement and Plan of Merger by and Between National Data
             Corporation, Universal Acquisition Corp., and Physician Support
             Systems, Inc.
             -------------------------------------------------------------
    
Ladies and Gentlemen:

        We have acted as counsel to National Data Corporation ("NDC"), a
corporation organized and existing under the laws of the State of Delaware, in
connection with the proposed merger of Universal Acquisition Corp., a wholly-
owned subsidiary of NDC ("Sub"), with and into Physician Support Systems, Inc.
("PSS"), a corporation organized and existing under the laws of the State of
Delaware, with PSS as the surviving corporation (the "Merger"). The Merger will
be effected pursuant to the Agreement and Plan of Merger among NDC, Sub, and PSS
dated as of October 14, 1997 (the "Agreement"). In our capacity as counsel to
NDC, our opinion has been requested with respect to the accuracy of the material
under the heading "Certain Federal Income Tax Consequences" in the registration
statement on Form S-4 to be filed by NDC on November 13, 1997, with the
Securities and Exchange Commission under the Securities Act of 1933, as amended,
(the "Registration Statement").

        In rendering this opinion, we have examined (i) the Internal Revenue 
Code of 1986, as amended (the "Code") and Treasury regulations, (ii) the 
legislative history of applicable sections of the Code, and (iii) appropriate 
Internal Revenue Service and court decisional authority. In addition, we have 
examined such documents as we have deemed appropriate, including the Agreement 
and the Registration Statement. In our examination of such documents, we have 
assumed, with your consent, that all documents submitted to us as photocopies 
faithfully reproduce the originals thereof, that such originals are authentic, 
that all such documents have been or will be duly executed to the extent 
required, and that all statements set forth in such documents are accurate.




 
National Data Corporation
November 7,1997
Page 2

        We have participated in the preparation of the material under the
heading "Certain Federal Income Tax Consequences" of the Registration Statement
and, assuming the Merger will be consummated in accordance with the terms of the
Agreement and will be valid under applicable Delaware law, we are of the opinion
that the federal income tax treatment described under such heading of the
Registration Statement is accurate in all material respects.

        The opinion expressed herein is based upon existing statutory,
regulatory, and judicial authority, any of which may be changed at any time with
retroactive effect. In addition, our opinions are based solely on the documents
that we have examined. Our opinion cannot be relied upon if any of the facts
contained in such documents or if such additional information is, or later
becomes, inaccurate, or if any of the statements set out herein is, or later
becomes, inaccurate. Finally, this opinion is furnished only to you, is solely
for your use in connection with the Registration Statement, and is limited to
the specific matters covered hereby.
        
        We hereby consent to the use of this opinion and to the references made
to the firm under the heading "Certain Federal Income Tax Consequences" and
"Legal Matters" in the Proxy Statement/Prospectus constituting part of the
Registration Statement.

                                                 Very truly yours,

                                                 ALSTON & BIRD

                                                 By: /s/ Pinney L. Allen
                                                     -------------------
                                                     Pinney L. Allen  
PLA: mmh