1 EXHIBIT 5.1 [VENTURE LAW GROUP LOGO] June 4, 1996 ISOCOR 3420 Ocean Park Boulevard Santa Monica, CA 90405 REGISTRATION STATEMENT ON FORM S-8 Ladies and Gentlemen: We have examined the Registration Statement on Form S-8 to be filed by you with the Securities and Exchange Commission on or about June 4, 1996 (the "Registration Statement") in connection with the registration under the Securities Act of 1933, as amended, of a total of 2,088,928 shares of your Common Stock (the "Shares") reserved for issuance under the 1996 Employee Stock Purchase Plan, the 1992 Stock Option Plan and the 1996 Directors' Stock Option Plan (collectively, the "Plans"). As your legal counsel, we have examined the proceedings taken and are familiar with the proceedings proposed to be taken by you in connection with the sale and issuance of the Shares under the Plans. It is our opinion that, when issued and sold in the manner referred to in the Plans and pursuant to the respective agreement which accompanies each grant under the Plans, the Shares will be legally and validly issued, fully paid and nonassessable. We consent to the use of this opinion as an exhibit to the Registration Statement and further consent to the use of our name wherever it appears in the Registration Statement and any amendments to it. Sincerely, VENTURE LAW GROUP /s/ Venture Law Group --------------------- EJB 2800 Sand Hill Road Menlo Park, CA 94025 Phone 415-854-4488 FAX 415-854-1121