Prostaglandins both stimulate and inhibit intestinal motility, inhibit gastric acid secretion, and influence glucose and glycogen metabolism in the liver. Their mechanisms of action have not been clearly defined, although it appears certain that their effects are closely involved with the adenylate cyclase-cyclic adenosine monophosphate system. Neither has it been determined whether these compounds play a role in gastrointestinal physiology. There are studies, however, to indirectly support this hypothesis. Similarities exist between the effects of cholera toxin, other bacterial toxins, and prostaglandin on water and electrolyte movement in the small intestine. Prostaglandins may play a role in the pathogenesis of the diarrhea and shock associated with bacterial infections. Prostaglandin analogues that promise to provide an effective means of decreasing gastric acid secretion in man are now being tested.