From mouse genomic libraries and human brain cDNA, we cloned three novel G-protein-coupled receptors (GPCRs), which have about 55–70% homologies with Xenopus PSP24 (xPSP24). Together with another human cDNA (GPR45) cloned by Marchese et al. (Genomics 56, 12–21, 1999). they comprise a family of mammalian PSP24s. Therefore, we termed these clones mouse PSP24α, β, and human PSP24α, β. The homologies between α and β isoforms were 54% for human and 51% for mouse clones. None of these clones shares sequence similarities with any known mammalian GPCRs, thus forming a unique gene family. Northern blot demonstrated that both of the mouse transcripts were predominantly expressed in the brain. In situ hybridization of brain sections showed that the expression was observed in neuronal cells, such as olfactory mitral cells, cortical neurons, hippocampal pyramidal cells, and Purkinje cells in the cerebellum. We suggest that mammalian PSP24 is a distinct GPCR family and plays a role in the brain function.