Two doses of epinephrine and norepinephrine were used (5 and 50 ng/kg per min i.v. in 1 h); the low dose of epinephrine and both doses of norepinephrine were considered to be physiologic. The low dose of epinephrine (n = 20) stimulated gastrin release and acid secretion, whereas the high dose (n = 18) stimulated the gastrin release strongly, but did not change acid secretion. Norepinephrine in the low dose (n = 11) caused a very small increase in gastrin release and no change in acid secretion without any change in gastrin concentration. No postoperative change was observed in the release of gastrin by both doses of epinephrine after truncal vagotomy in 6 and 7 patients with duodenal ulcer. Epinephrine and norepinephrine both may be of importance in the physiological regulation of gastrin release and gastric acid secretion.