Alkaline secretion measured under basal conditions in the intact stomach of conscious dogs averaged 47 mumol/30 min and was about twice lower than that recorded in the proximal (approximately 7 cm long) portion of the duodenum. Vagal excitation elicited by sham feeding and insulin resulted in a marked stimulation of alkaline secretion both from the stomach and the duodenum. Atropine significantly reduced gastric and duodenal alkaline secretion under basal state. It abolished gastric and diminished duodenal alkaline response to sham feeding and insulin hypoglycemia, while propranolol was without significant influence. Indomethacin reduced by approximately 75% basal duodenal alkaline secretion but did not prevent the increment in alkaline response to vagal stimulation. We postulate the existence of the cephalic phase of gastroduodenal alkaline secretion, which seems to be cholinergically dependent in the stomach and partly of noncholinergic and nonadrenergic character but prostaglandin dependent in the duodenum.