Gastric and esophageal emptying were measured using scintigraphic techniques in 16 patients with dystrophia myotonica and in 22 normal volunteers. Gastric emptying of a solid meal was slower than the normal range (defined as the mean +/- two standard deviations obtained in the normal volunteers) in 15 of the 16 patients, and gastric emptying of the liquid meal was slower than the normal range in 10 of the patients. Esophageal emptying was also markedly delayed in patients, with 15 of 16 patients having an emptying time longer than the normal range. There was no relationship between gastrointestinal symptoms, or the severity of the peripheral (skeletal) muscle weakness, and either gastric or esophageal emptying. Oral administration of metoclopramide resulted in a significant improvement in gastric emptying of the solid meal and a nonsignificant trend toward more rapid liquid emptying, but no change in esophageal emptying. These results indicate that there is a very high prevalence of gastric and esophageal smooth muscle dysfunction in dystrophia myotonica and that gastroparesis is likely to be a treatable cause of morbidity in this disease.