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                                                                     EXHIBIT 5.1



                                    C/255/74

                      Tel Aviv, Tuesday, January 18, 2000

CommTouch Software Ltd.
6 Hazoran Street
Poleg Industrial Park, P.O. Box 8511
Netanya 42504
Israel
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Ladies and Gentlemen:

     We refer to the Registration Statement on Form S-8 (the "Registration
Statement") to be filed by CommTouch Software Ltd. (the "Company") with the
Securities and Exchange Commission on or about January 18, 2000 in connection
with the registration under the Securities Act of 1933, as amended, of an
aggregate of 5,400,000 of the Company's Ordinary Shares (the "Shares") reserved
for issuance under the Company's 1996 CSI Stock Option Plan, the Company's 1999
Section 3(i) Share Option Plan, the Company's 1999 Employee Stock Purchase Plan
and the Company's 1999 Nonemployee Directors Stock Option Plan (collectively,
the "Option Programs").

     As legal counsel to the Company, we have examined such corporate records
and documents and such questions of law as we have considered necessary or
appropriate for the purpose of this opinion. Upon the basis of such
examination, we are of the opinion that the Shares, when issued and sold
pursuant to the applicable provisions of the Option Programs and the agreements
which accompany the Option Programs, and in accordance with the Registration
Statement, will be legally and validly issued, fully paid and non-assessable.

     We consent to the filing of this opinion as an exhibit to the Registration
Statement and further consent to the use of our name wherever appearing in the
Registration Statement, including any prospectus constituting a part thereof,
and any amendments thereto.


                                             Very truly yours,


                                             /s/ Naschitz, Brandes & Co.
                                             ----------------------------
                                                 Naschitz, Brandes & Co.