We have isolated the gonadotropin-releasing hormone receptor (GnRH-R) from a rat anterior pituitary cDNA library, determined its sequence and demonstrated receptor function. The 2.2 kb rat GnRH-R clone encodes a protein of 327 amino acids. A 1.3 kb clone encoding the mouse GnRH-R has previously been described (Tsutsumi et al., 1992). Although both the mouse and rat protein share significant homology with molecules belonging to the family of G protein-coupled receptors, they have certain unusual features, an example being the complete absence of a COOH terminal tail. The 3'-untranslated region reported missing in the mouse is present in the rat cDNA, where an extended 1 kb of 3'-untranslated region extending to the poly-A tail is shown. At the amino acid level, the rat GnRH-R shows considerable homology with that of the mouse. Electrophysiological studies with Xenopus oocytes and transfection of the cDNA into COS-1 cells, have shown that the 2.2 kb cDNA clone encodes a functional receptor.