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                                                                     EXHIBIT 8.1

                                       October 29, 1997

F.N.B. Corporation
Hermitage Square
Hermitage, Pennsylvania  16148

West Coast Bank
3700 South Tamiami Trail
Sarasota, Florida 34239

         Re:   Agreement and Plan of Merger under which West Coast Bank
               will merge with and into Southwest Interim Bank No. 3, to be a
               wholly-owned subsidiary of F.N.B. Corporation

Ladies/Gentlemen:

         We have acted as special counsel to F.N.B. Corporation ("FNB") in
         connection with the proposed merger (the "Merger") of West Coast Bank
         ("West Coast") with and into Southwest Interim Bank No. 3 ("Interim"),
         which will be a wholly-owned subsidiary of FNB, pursuant to the terms
         of and as described in that certain Agreement and Plan of Merger (the
         "Merger Agreement") dated as of August 13, 1997 and amended as of
         October 16, 1997, by and among FNB, Interim, Southwest Banks, Inc.
         ("Southwest") and West Coast, described in the FNB Registration
         Statement on Form S-4, to be filed with the Securities and Exchange
         Commission on or about October 20, 1997 (the "Registration Statement").
         At your request, in connection with the filing by FNB of the
         Registration Statement and the Proxy Statement-Prospectus of West Coast
         and FNB (the "Proxy Statement-Prospectus") included as part of the
         Registration Statement, we are rendering our opinion concerning certain
         federal income tax consequences of the Merger. Unless otherwise
         indicated, all capitalized terms used in this opinion have the same
         meaning as used in the Proxy Statement-Prospectus.

         For purposes of rendering our opinion herein, we have conducted an
         examination of the Internal Revenue Code of 1986, as amended (the
         "Code"), and such other applicable laws, regulations, rulings,
         decisions, documents and records as we have deemed necessary. With
         respect to factual matters, we have relied upon the Merger Agreement,
         including, without limitation, the representations of the parties set
         forth therein, and upon certain statements and representations made to
         us in certificates by officers of FNB and West Coast, in each 

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         case without independent verification thereof. With the consent of FNB
         and West Coast, we have relied on the accuracy and completeness of the
         statements and representations contained in such certificates and have
         assumed that such certificates will be complete and accurate as of the
         Effective Time. We have also relied on the accuracy and completeness of
         the Proxy Statement-Prospectus. In addition, for purposes of this
         opinion, we have assumed that at least fifty percent of the outstanding
         shares of West Coast Common Stock will be exchanged for FNB Common
         Stock in the Merger, and that the shares of West Coast Common Stock
         constitute capital assets in the hands of each holder thereof.

         Based on the foregoing, and subject to the qualifications set forth
         below, we are of the opinion that under the Code:

         (1) The Merger will constitute a reorganization under Code ss.ss.
         368(a)(1)(A) and 368(a)(2)(D), and FNB, Interim and West Coast will
         each be a party to the reorganization within the meaning of Code
         ss.368(b).

         (2) Holders of shares of West Coast Common Stock who exchange such
         shares solely for shares of FNB Common Stock will not recognize gain or
         loss on the exchange.

         (3) The federal income tax basis of shares of FNB Common Stock received
         in exchange for shares of West Coast Common Stock will be equal to the
         holder's basis of the shares of West Coast Common Stock surrendered in
         exchange therefor, and the holding period of such FNB Common Stock will
         include the holding period of the West Coast Common Stock surrendered
         in exchange therefor.

         (4) The receipt of cash in lieu of fractional shares will be treated as
         if the fractional shares were distributed as part of the exchange and
         then redeemed by FNB, and capital gain or loss will be recognized in an
         amount equal to the difference between the cash received and the basis
         of the fractional share of FNB Common Stock surrendered.

         (5) A holder of West Coast Common Stock who exercises appraisal rights
         will recognize capital gain or loss equal to the difference between the
         cash received and such holder's tax basis in the West Coast Common
         Stock exchanged.

         The opinions expressed herein are based upon our interpretation of
         existing legal authorities, and no assurance can be given that such
         interpretations would be followed if the exchange of shares
         contemplated by the Merger became the subject of administrative or
         judicial proceedings. Statements of opinion herein are opinions only
         and should not be interpreted as guarantees of the current status of
         the law, nor should they be accepted as a guarantee that a court of law
         or administrative agency will concur in such statement.

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         No opinion is expressed with respect to any of the following:

         (i) The appropriate method to determine the fair market value of any
         stock or other consideration received in any sale or exchange;

         (ii) The state, local or foreign tax consequences of any aspect of the
         Merger; or

         (iii) The federal income tax consequences of any aspect of the Merger
         to holders of West Coast Common Stock who are subject to special tax
         treatment for federal income tax purposes, including among others, life
         insurance companies, tax exempt entities and foreign taxpayers, or to
         holders of warrants or options to purchase West Coast Common Stock, if
         any, which are exchanged for or converted into options or warrants to
         acquire FNB Common Stock.

         We expressly consent to the filing of this opinion with the Securities
         and Exchange Commission as an exhibit to the Registration Statement,
         and to the references to this opinion in the Proxy
         Statement-Prospectus. In giving this opinion, we do not hereby admit
         that we are in the category of persons whose consent is required under
         Section 7 of the Securities Act of 1933, as amended.

                                         Very truly yours,

                                         SMITH, GAMBRELL & RUSSELL, LLP

                                         /s/ David W. Santi

                                         David W. Santi


DWS/dkaw