Avian erythroblastosis virus (AEV) induces acute erythroleukemia and sarcomas in vivo and it transforms erythroblasts and fibroblasts in vitro. The virus has two host cell-derived genes, v-erbA and v-erbB. The latter encodes the oncogenic capacity of the virus, whereas v-erbA enhances the erythroblast transforming effects of v-erbB while being unable to induce neoplasms independently. Recently, human cellular homologues of these viral erb genes have been isolated. The chromosomal locations of two of these genes have been determined using EcoRI-digested DNA prepared from human-mouse somatic cell hybrids. The human c-erbA1 gene has been assigned to chromosome 17 and is located between 17p11 and 17q21. The human c-erbB sequence has been assigned to chromosome 7 and is located between 7pter and 7q22. Thus, in the human genome these genes are on two separate chromosomes. No evidence for the involvement of the human c-erb genes in neoplasia has been found.