We previously reported that the structural gene for epidermal growth factor receptor (EGFR) can be mapped to the p22→qter region of human chromosome 7 (Shimizu et al., 1979, 1980). In the present study, we produced two series of human-mouse cell hybrids by fusing mouse A9 cells that are deficient in EGFR with the human diploid fibroblast lines GM1356, 46, XX, t(l;7)(p34;pl3), and GM2068, 46, XX, t(6;7)(q27;q22), both of which possess EGF receptors. Expression of EGF binding ability in the former series of cell hybrids was correlated with the retention of the human translocation chromosome containing the 7p13→qter region, and in the latter series of cell hybrid it was correlated with the retention of the human translocation chromosome containing the 7pter→q22 region. Therefore, the EGFR gene can be localized in the p13→q22 region of chrom