The data of the Third National Cancer Survey show for many cancer types, large differences in cancer incidence between Euro-Americans and Afro-Americans.(1) As in other racial studies, it is difficult to separate environmental and genetic factors. For the cancers which are more frequent among Afro-Americans, environmental factors seem to be primarily responsible. However, among the cancers less frequent in Afro-Americans, there are some for which the racial differences have a genetic basis. This is clearly the case for skin and lip cancers caused by the ultraviolet B of the sun. Genetic factors are probably also responsible for the racial differences in the incidence of malignant melanomas, testis cancers, astrocytomas, and Ewing's sarcomas. Perhaps there is also a genetic basis for some of the racial differences in the incidence of malignant lymphomas and leukemias. For all these cancers, Afro-Americans are less susceptible. The only cancer to which Afro-Americans appear more susceptible on the basis of genetic makeup, is fibrosarcoma. This is in accord with the high frequency of keloids, a benign counterpart of fibrosarcoma in Afro-Americans.