PCP-GABA, an analogue of the neurotransmitter amino acid, GABA, is as effective a stimulant of vagal centers and acid secretion as sham feeding. Insulin hypoglycemia, a test hitherto widely used for the cephalic phase, is unsafe and nonspecific because it also stimulates catecholamine release which affects gastrin secretion. PCP-GABA, unlike insulin, causes no tachycardia or hypoglycemia; however, the major advantage of PCP-GABA is that it can be used safely intraoperatively to assess completeness of vagotomy. Its muscle relaxant action is an additional advantage in this regard. As an intraoperative test, PCP-GABA is given intravenously shortly after induction of anesthesia to stimulate acid secretion and to reduce gastric mucosal pH, which is measured by an intraluminal combination electrode. The electrode can be moved around through the intact gastric wall to take measurements from multiple sites. When vagotomy is complete, gastric mucosal pH increases to over 6. This test works well in the dog. We hope to assess its clinical use in the near future.