Canines with vagally innervated fundic pouches and chronic esophageal fistulas were subjected to sham feeding experiments during which pouch acid output and peripheral serum gastrin levels were measured. These dogs then underwent construction of vagally innervated antral pouches. The sham feeding experiments were repeated after recovery. Preoperatively sham feeding provoked a substantial increase in acid output accompanied by a small serum gastrin increase which did not achieve statistical significance. After creation of the innervated antral pouches, sham feeding evoked an acid secretory response similar to control values. Serum gastrins, however, increased nearly 500 percent in response to sham feeding. Our data support the concept that direct vagal stimulation of the parietal cell mass is the major mechanism by which sham feeding increased acid secretion.