The interdigestive gastroduodenal motor activity and serum motilin levels were studied in 22 dyspeptic patients with markedly delayed gastric emptying not due to diseases known to impair gastroduodenal motility and in 7 control subjects with normal gastric emptying. Motor activity was recorded using a manometric probe positioned in the gastric antrum and in the proximal duodenum, and blood samples for radioimmunoassay of motilin were taken every 15 min during the recording period. The control subjects showed gastroduodenal activity fronts of the migrating motor complex associated with motilin peaks. Almost all patients with delayed gastric emptying showed no activity fronts in the stomach, and only half of them showed activity fronts starting in the duodenum. In these patients a significant reduction in the number of motilin peaks and in the integrated motilin output during the identified peaks was also observed. The results of this study indicate that most dyspeptic patients with idiopathic delay in gastric emptying may also have an alteration in interdigestive gastroduodenal motility, mainly characterized by a lack of gastric activity fronts, associated with an impaired motilin release.