A case of adult idiopathic hypertropic pyloric stenosis whose radiographic study was repeatedly normal is presented. Only a functional test of gastric emptying disclosed the degree of outlet obstruction present. Vagotomy and pyloroplasty resulted in prolonged relief of obstructive symptoms and a return of the saline load test to normal. The saline load test may be of value when gastroduodenal x-rays or endoscopy do not reveal the cause or extent of gastric outlet obstruction.