The development of obesity in the Pima Indians may in part be determined by the rates of gastric emptying. Furthermore, peptic ulcer disease is known to be low in this population, but increasing. Studies of gastric emptying and gastric acid secretion to a date suggest that rates of liquid gastric emptying are not altered in obesity. Diabetes appear to be associated with decreased acid secretion and hypergastrinemia. The low acid production in the Pima Indians may explain the low incidence of gastroduodenal ulceration.