The histamine H2 receptor is a widely distributed G-protein coupled receptor, which is important in regulating a host of physiologic actions extending from gastric acid secretion to gastrointestinal motility. Histamine mediated activation of its receptor leads to signaling through both adenylate cyclase and phosphoinositide/protein kinase C second messenger systems. Antagonists for this receptor have proven to be effective therapy for acid peptic disorders of the GI tract. Certain antagonists are used in the treatment of neuropsychiatric and neurological diseases e.g. schizophrenia, Alzheimer"s disease and Parkinson"s disease.