Intravenous erythromycin has been shown to improve gastric emptying in diabetic gastroparesis. Oral erythromycin also accelerates gastric emptying, but to a lesser degree. To determine if this is a dose-dependent phenomenon, gastric emptying was measured in 10 insulin-requiring diabetic patients with gastroparesis after administration of either 250 mg or 1000 mg of erythromycin or placebo. The drugs were orally administered in a randomized, double-blind fashion 30 min prior to ingestion of a meal containing [99mTc]-sulfur colloid-labeled beef stew and [111In]DTPA-labeled orange juice. Anterior and posterior gastric images were recorded for 3 hr at 15-min intervals using an externally positioned gamma camera. The results demonstrated that both doses of oral erythromycin significantly improved solid-phase gastric emptying. The mean half-emptying time of solids was decreased from 151 +/- 40 min with placebo to 58 +/- 10 min and 40 +/- 9 min with 250 mg and 1000 mg of erythromycin, respectively. However, a dose-dependent relationship was not demonstrated with the two doses of erythromycin employed. These results suggest that for most patients with diabetic gastroparesis, a single 250-mg dose of erythromycin will significantly improve gastric emptying. It is possible that a dose-dependent relationship will be demonstrated with doses of erythromycin less than 250 mg.