Gonadotropin-releasing hormone (GnRH) has been shown to play a role in the regulation of human chorionic gonadotropin (hCG) secretion by the human placenta. Molecular studies have demonstrated that human placental trophoblast cells synthesize a progonadotropin-releasing hormone (pro-GnRH) identical to its human hypothalamic counterpart. However, far less is known about nonhuman primates. To determine whether pro-GnRH exists in the rhesus placenta, pro-GnRH mRNA was cloned, sequenced, and shown to be 97.6% homologous to its human placental counterpart. A single base difference (base 1167) in the domain encoding GnRH results in the same amino acid, arginine, in position 8, whereas four base differences (bases 1200, 1253, 1268, 1292) in the domain encoding GnRH-associated peptide (GAP) result in four different amino acids in position 19, 37, 42, and 50. The absence of a basic amino acid in position 50 suggests the rhesus sequence may be cleaved to yield GAP peptides different from the human placenta. Thus, these data justify the use of mammalian GnRH in studies of rhesus placental function, but indicate the need to investigate the roles unique GAP peptides may play in placental/uterine function.