This chapter has focused on many of the gut hormones that regulate gastric function. Gastrin remains the principal, and only, gastric hormone controlling gastric acid secretion during the cephalic, gastric and intestinal phases of secretion. Several other hormones, including cholecystokinin, peptide YY and secretin, released from intestinal endocrine cells in response to food substrates, have significant inhibitory effects on gastric acid secretion. Many of these hormones, including enteroglucagon and glucagon-like peptide, may act through paracrine release of somatostatin, which in turn acts as the final mediator of acid inhibition. In addition, several peptides contained in nerves, including gastrin releasing peptide and vasoactive intestinal peptide, have been shown to regulate gastric acid secretion and motor function. With the creation of specific monoclonal antibodies for use in in vivo immunoneutralization studies, and the development of selective chemical antagonists for use in receptor blockade experiments, the specific contributions of the different gut hormones in the regulation of gastric function, can be assessed. © 1994 Baillière Tindall.