To investigate the role of motilin in diabetic gastroparesis, we evaluated gastric emptying and plasma concentrations of motilin in diabetic patients. Gastric emptying of radiopaque marker was significantly delayed in the diabetics with autonomic neuropathy (n = 14) compared with the healthy controls (n = 6) (p < 0.01). Mean plasma motilin concentrations were significantly higher in the diabetics with autonomic neuropathy compared with the healthy controls (p < 0.01). A positive correlation was observed between gastric emptying and plasma motilin concentrations in the healthy controls (r = 0.955, p < 0.01), whereas these values were inversely correlated in the diabetics (r = 0.620, p < 0.01). Oral administration of cisapride (15 mg/day.14 day) significantly accelerated gastric emptying without an effect on plasma motilin concentration (p = 0.03). These observations suggest that gastric emptying in the diabetics with autonomic neuropathy is delayed despite elevated levels of motilin, and that cisapride accelerates gastric emptying, independent of the plasma motilin concentration.