Interdigestive gastroduodenal motility was studied manometrically in 16 patients with ulcer-like dyspepsia due to hypersecretory gastroduodenitis (group A) and in a control group of 6 healthy subjects (group B). After a basal recording period sufficient to record at least two activity fronts (AF) of the migrating motor complex (MMC) of the gastroduodenal tract, we administered 100 mg of ranitidine intravenously to 8 patients of group A (group A1), and the same dose of ranitidine to the remaining 8 patients of group A (group A2) after pretreatment with cimetidine 200 mg i.v. to block the acid secretion. The interdigestive motility of patients with hypersecretory gastroduodenitis is characterized by a decrease in frequency and duration of the activity fronts of MMC, which may play a role in the pathogenesis of mucosal lesions. Ranitidine induced premature and prolonged activity fronts in all patients without antisecretory pretreatment, and in the majority of patients in whom the acid secretion was previously blocked.