Considerable progress has been made in the understanding of the formation of gastric erosions in rats. The role of gastric acid secretion in their pathogenesis has been clarified. Gastric erosions are also associated with slow gastric contractions. With several experimental procedures, the body temperature falls; preventing this decrease averts erosions. A fall in body temperature or exposure to cold is associated with the secretion of thyrotropin-releasing hormone (TRH), and both an increase and decrease in corticotropin-releasing factor (CRF) in discrete regions of rat brains. TRH produces gastric erosions, increases in acid secretion, and slow contractions, while CRF has the opposite effects. One of the major sites of interaction of the two peptides is in the dorsal motor complex of the vagus nerve. TRH increases serotonin (5-HT) secretion into the stomach. 5-HT counter-regulates acid secretion and slow contractions. Many other peptides stimulate or inhibit gastric acid secretion.