Gastric emptying was studied with a double radioisotopic method in 12 patients with insulin-dependent diabetes mellitus complicated by autonomic neuropathy and in 22 control subjects. In the diabetics, the acute and chronic effects of oral domperidone on gastric emptying, symptoms of gastroparesis, and glycemic control were assessed. Gastric emptying of solid and liquid was slower in diabetics than controls (P less than 0.001). Acute administration of domperidone increased the rate of both solid and liquid emptying (P less than 0.005). Domperidone was most effective in those patients with the greatest delay in gastric emptying. After chronic administration (35-51 days), domperidone had no significant effect on solid emptying (P greater than 0.05), but was still effective in increasing liquid emptying (P less than 0.025). Symptoms of gastroparesis were less after domperidone (P less than 0.001).