The fact that histamine H2-receptor antagonists strongly inhibit basal and nocturnal gastric secretion and acid secretion stimulated by histamine, pentagastrin, caffeine, insulin, sham feeding and food indicate that histamine plays a physiological role in gastric acid secretion. Histamine is thus regarded as the final common chemical mediator at the oxyntic cell. Also it has been proposed that there are at least three stimulatory receptors in the parietal cell wall (histamine, acetylcholine and gastrin). Each stimulant acts on its own receptor. Interactions consisting of potentiation occur between histamine and gastrin, histamine and acetylcholine and between histamine, gastrin and acetylcholine, but not between gastrin and acetylcholine because all potentiating interactions require histamine.