Recently a novel subfamily of closely related orphan G protein-coupled receptors (GPCRs) was identified, called GPRC5A, GPRC5B, GPRC5C and GPRC5D. Based on sequence homology, these receptors were classified as family C GPCRs, which include metabotropic GABA(B) receptors, metabotropic glutamate receptors, the calcium sensing receptor and a number of pheromone receptors. GPRC5 receptors share approximately 30-40% sequence homology to each other and 25% homology to the other family C members. It has been shown human GPRC5B mRNA is predominantly expressed in the central nervous system. In order to further characterise this receptor, we investigated both the mRNA and protein expression profiles in rodent tissues. Western blot analysis, using affinity-purified antisera specific to GPRC5B, identified a protein migrating at approximately 68 kDa, close to the predicted molecular weight for GPRC5B. Immunocytochemical analysis of GPRC5B-transfected cells revealed a cell surface localisation. In addition, immunohistochemical analysis of GPRC5B in rat brain and spinal cord demonstrated receptor expression in many areas, with highest levels of immunoreactivity in the neocortex, all subfields of the hippocampus, the granule cell layer of the cerebellum and throughout the spinal cord.