Sarcomas induced by the chemical carcinogen 3-methyl-cholanthrene (MC) in pedigreed BALB/c strain mice were studied for the existence and characteristics of tumor-specific antigens that induce protective immune defenses in syngeneic mice (TATA). It was found that each of the neoplasms expressed a unique immunogenicity that was stable and heritable over a period of 125 transfers in vivo. Common or crossreacting TATA were not observed. When converted to an ascitic form, two of these sarcomas, CII-7 and CII-10, were found to be crossreactive, presumably sharing TATA with each other and with the MC-induced sarcoma Meth A. Two other neoplasms converted to the ascitic form, however, retained their unique TATA. Although the precise nature of unique and crossreacting TATA is not known, it is hoped that recent investigations in the purification of TATA of chemically induced neoplasms will shed light on the mechanisms responsible for the diversity of tumor-specific antigens.