Serological evidence is presented that two chemically-induced (by methylcholanthrene and 3,4-benz(a)pyrene) sarcomas of C3HF mice contain cross-reacting tumor-associated cell-surface antigens. Xenogeneic and syngeneic antitumor antisera against the two sarcomas were studied with an isotopic, complement-dependent, antibody-mediated microcytotoxicity assay and an isotopic antiglobulin test for the detection of antibodies to tumor-associated antigens, in vitro. Absorportions with various tissues were performed which consistently revealed that the specific activity of the antitumor antisera could be removed by absorption with cells from either chemically-induced tumor, while absorption with syngeneic normal adult tissues, normal fetal tissues, or cells from a histogenetically unrelated tumor (spontaneous mammary carcinoma) failed to remove any specific activity. In view of the individual character of carcinogen-induced tumor antigens as detected by tumor transplantation techniques, our results suggest that chemically-induced murine sarcomas (even when induced by different carcinogens) contain both private and common cell-surface antigens, the latter detectable by serological methods. These common tumor-associated antigens may be related to a viral genome involved in the nalignant transformation of carcinogen-induced marine sarcomas.