Glucagon-Like Peptide I (7-36) (GLP)-1 (7-36)-NH2 is a peptide found in the mucosal endocrine cells of the intestine, and plasma levels of Glucagon-Like Peptide I (7-36)-NH2 immunoreactivity show a rise after the ingestion of a fat or mixed-component meal. The effects of physiological infusion of Glucagon-Like Peptide I (7-36)-NH2 on a submaximal gastric acid secretion in healthy volunteers at a rate known to mimic the observed postprandial rise in plasma concentrations. Some results suggest a novel role for Glucagon-Like Peptide I (7-36)-NH2 as a physiological inhibitor of gastric acid secretion in humans.