A mouse histamine H2 receptor (H2R) gene was isolated from a mouse ES cell genomic DNA library. The gene encoded a 358-amino-acid protein and displayed a 95% homology with the rat histamine H2 receptor at the amino acid level. It had features characteristic of other G-protein-coupled receptors. Reverse transcriptase-polymerase chain reaction analysis of total RNA prepared from mouse tissues showed that the gene was highly expressed in stomach and moderately in brain and heart. A weak expression was also detected in liver. An interspecific backcross analysis revealed that the mouse H2R gene, designated Hrh2, was located in the central region of chromosome 13.