The proposed investigations will continue an ungoing study aimed at investigating changes in morphology and secretory capacity of the gastric mucosa induced by topical exposure to intestinal contents. Stomachs chronically exposed to intestinal juices will be examined over prolonged periods of time for acid and pepsin secretory capacities, parietal cell numbers, gastrin cell numbers, and for histologic changes of gastritis. The second broad objective is to study factors controlling the reflux of duodenal contents into the stomach in the dog and in the human. Autonomic, pharmacologic, hormonal, and lumenal influences on duodenal-gastric regurgitation will be evaluated. Human studies will be carried out by radiographic techniques and by quantitation of bile in aspirated gastric contents; animal studies will employ a radioactive marker of duodenal contents. Two basic problems to be explored are: (1) What are the effects of exposing antral and corpus mucosa to intestinal juices? (2) What factors determine passage of duodenal juices into the stomach.