Prostaglandins (PGD2, PGE2, PGF2 alpha, and PGI2) and thromboxane A2 (TXA2) are biologically active molecules derived from the metabolism of arachidonic acid by cyclooxygenases. They produce a wide variety of physiological and pathophysiological effects mediated through specific G protein-coupled cell surface receptors. In this study, we have mapped the chromosomal positions of the human genes that encode the PGE2 receptor subtypes (PTGER1, PTGER2, and PTGER3), the PGF2 alpha receptor (PTGFR), the PGI2 receptor (PTGIR), and the TXA2 receptor (TBXA2R) using in situ hybridization. The PTGER1, TBXA2R, and PTGIR genes mapped to chromosome 19 at positions 19p13.1, 19p13.3, and 19q13.3, respectively. The PTGFR and PTGER3 genes mapped to chromosome 1 at positions 1p31.1 and 1p31.2, respectively, and PTGER2 gene mapped to chromosome band 5p13.1.