The existence of tumor-specific antigens in fibrosar

comas induced by aromatic hydrocarbons has been well established by Foley (2), Klein (8), Old (11), Prehn (12— 14), and others; but data on the antigenicity of spon taneously arising tumors in sparse. Morton (10) re ported briefly that the temporary growth of the first transplant generation of a spontaneous mammary adeno carcinoma in C3HJHEN mice conferred a significant degree of immunity to subsequent transplants of the same tumor. Prior treatment with normal tissue from the tumor donor provided no immunity. In the present study the induction of immunity in C3H/HEN mice to a spontaneously arising adenocar cinoma of the breast has been confirmed but found to be less than that induced by a methylcholanthrene-induced fibrosarcoma. The immunity appeared to be specific for the immunizing tumor, and the degree of immunity was related to the time interval between removal of the immunizing tumor and inoculation of the second tumor transplant.