The gene for the cell surface receptor for HTLV-I, the etiologic agent of adult T-cell leukemia and HTLV-I-associated myelopathy, has been localized to distal human chromosome 17q. A panel of somatic cell hybrids containing fragments of human 17q as the only human genetic component was mapped with a set of 10 chromosome 17 probes and utilized to regionally localize the gene. When compared to the murine fibroblast fusion partner, L-M(TK-), and a hybrid cell line containing human chromosome 20, human 17q-containing hybrid cells bound high levels of both HTLV-I virions and the monoclonal antibody, Mab 34-23, which may be directed against the putative HTLV-I receptor. Additional experiments revealed that the human 17q-containing hybrids could also be more efficiently infected by cell-free HTLV-I virions than could the control cell lines. Western blot analyses of cell lysates showed that recombinant HTLV-I envelope gp46 protein and Mab 34-23 both bound to proteins of approximate MW 30 and 31 kDa which were found only in the hybrid cell lines which contained human chromosome 17q. The data suggest that the gene for the HTLV-I receptor is located on the distal region of human chromosome 17q demarcated by the tk-1 locus (17q23.2-17q25.3).