A novel gene product, GPR56, with homology to the seven transmembrane-domain receptor superfamily, has been cloned by PCR amplification using degenerate oligonucleotide primers and subsequent screening of a human heart cDNA library. The isolated 2.8-kb cDNA clone encodes a protein of 693 amino acids that shows highest identity (32%) to HE6, a member of a subclass of the class B secretin-like G-protein-coupled receptors. Northern analysis of various human tissues revealed a wide distribution of the transcript with highest levels found in thyroid gland, brain, and heart. In situ hybridization analysis of human thyroid gland as well as rat heart and brain tissue confirms these results and identifies the hippocampus and hypothalamic nuclei as brain areas with particularly high expression of GPR56 mRNA. The high level of mRNA expression, its wide distribution, and the mucin-like extracellular domain of the receptor protein suggest a possible role for this receptor in cell-cell interaction processes. The human gene for GPR56 has been isolated and its exon-intron structure determined. The total length of the human GPR56 gene is approximately 15 kb, and it consists of 13 exons. Fluorescence in situ hybridization, PCR analysis of somatic cell hybrids, and interspecific mouse backcross mapping have localized the genes to human chromosome 16q13 and mouse chromosome 8.