A cDNA representing the high-affinity gonadotropin-releasing hormone (GnRH) receptor has been molecularly cloned from the human pituitary gland, a breast tumor cell line (MCF 7), and an ovarian tumor. The nucleotide sequence of this cDNA was determined, and its expression in various human tumors and tumor cell lines was demonstrated. In this study, we localized the gene encoding the GnRH receptor to human chromosome 4, using polymerase chain reaction (PCR) analysis of genomic DNA from human x hamster somatic cell hybrids. The gene was sublocalized to chromosome band 4q13 using fluorescence in situ hybridization with the GnRH receptor gene (GNRHR).