Extracellular nucleotides mediate a number of physiological responses through either ligand gated P2X or G protein-coupled P2Y receptors. To date, six P2Y receptor subtypes, P2Y1-P2Y6, have been cloned. We mapped the human P2Y6 receptor gene to chromosome 11q13.3-13.5. Oligonucleotide primers complementary to a part of the human P2Y6 receptor cDNA were used to amplify a region from genomic DNA from a panel of mouse/human somatic cell hybrid cell lines, each containing a single human chromosome. A PCR product of the expected size (714 bp) resulted from a single hybrid cell line containing human chromosome 11. The gene was further localized to a region of chromosome 11 using a subchromosomal hybrid panel containing different segments of chromosome 11. Based on the specific PCR product obtained and its Southern hybridization to the P2Y6 receptor cDNA, the human P2Y6 receptor gene was localized to chromosome 11q13.3-13.5. Previously, we have localized the P2Y2 receptor gene to human chromosome 11q13.5-14.1. This is the first report of the clustering of the P2 receptor genes. The clustering of these two P2Y receptor subtypes suggests a relatively recent expansion of the gene family by gene duplication.