Growth factors regulate mucosal growth and adaptation to mucosal injury and intestinal resection. A number of peptide growth factors have been identified, including epidermal growth factor, transforming growth factor-α, insulinlike growth factor-l, and fibroblast growth factors. A series of articles are reviewed which emphasize that a number of peptide growth factors promote epithelial cell proliferation in response to injury. These studies provide some initial insights into mechanisms involved in ulcer healing. Understanding of physiologic events in the gastric and intestinal phases of gastric acid secretion have been aided by specific peptide receptor antagonists and monoclonal antibodies capable of neutralizing circulating peptide hormones. Application of these techniques has revealed that gastrin is a principal mediator of meal-stimulated acid secretion. Furthermore, somatostatin and cholecystokinin have been shown to inhibit gastric acid secretion when acid and fat, respectively, are introduced into the intestine. The concept of nonadrenergic noncholinergic inhibitory neural mechanisms has been reconfigured with the demonstration that nitric oxide is capable of inhibiting gastrointestinal smooth muscle and acting as a mediator of vasodilatation. It is clear that nitric oxide is an important inhibitory neurotransmitter and cell-derived mediator within the gastrointestinal tract.