Gastroparesis is a relatively uncommon but clinically troublesome disorder that develops in some patients with diabetes mellitus or after gastric operations. Its pathogenesis remains obscure. We used a manometric technique to record pressure changes in fasting patients in the gastric fundus, distal stomach, and adjacent small bowel of patients with severe gastroparesis, asymptomatic diabetic patients, asymptomatic postsurgical patients, and healthy controls. Patients with gastroparesis had normal interdigestive motor cycles (phase III) in the intestine but not in the stomach. Sporadic motor activity in the stomach (phase II) also was markedly reduced. Metoclopramide and bethanecol significantly increased gastric motor activity in these patients, often triggering an intense burst of motor activity in the stomach, similar to phase III. These observations suggest that gastroparesis is a potentially reversible disorder and should encourage further attmpts for pharmacologic control of the syndrome.