We isolated a 40 kDa integral membrane protein (p40) from human erythrocyte ghosts by affinity chromatography, using a C-terminal peptide of stomatin, and obtained partial sequences which enabled us to isolate two full-length cDNAs from human bone marrow and fetal brain cDNA libraries. The cDNA sequences were identical and encoded a novel putative G protein-coupled receptor (399 amino acids). Northern and RNA dot blot analyses demonstrated that the major 4.8 kb-transcript is predominantly expressed in brain. In situ hybridization studies of tissue sections revealed high expression in neurons of the brain and spinal cord, in thymocytes, megakaryocytes, and macrophages.