The effect of antral acidification on the antral and cephalic phases of gastric secretion has been studied. Cross-transfusions were carried out between pairs of dogs in which blood from the portal vein of one dog was administered to another dog with a denervated fundic pouch. Transfusion of blood collected during acidification of the antrum resulted in a diminution of Heidenhain pouch acid secretion in response to food and to topical acetylcholine of 64% and 83%, respectively. The effect of antral acidification on gastric secretion stimulated by insulin hypoglycemia was studied in dogs prepared with Pavlov and isolated antral pouches (innervated and denervated). Irrigation of the antral pouch with .1 n hydrochloric acid resulted in a 92% decrease in Pavlov pouch acid output.