The interdigestive gastroduodenal motility was studied by means of a multilumen manometric probe in eight patients with active duodenal ulcer (group DU1) and in seven patients with hypersecretory gastroduodenitis (group GD). Both groups were selected on the basis of the presence of gastric acid hypersecretion. A group of five patients with non-active duodenal ulcer (group DU2) and a group of eight healthy subjects (group C) also were examined. Both of the latter groups were selected on the basis of the presence of normal gastric secretion. After a basal recording period of 200-300 min, in hypersecretory groups DU1 and GD, ranitidine was administered to decrease acid secretion; in normosecretory groups C and D2, impromidine was infused at two scalar doses to increase acid secretion. The basal recording showed in groups DU1 and GD a longer than normal time interval between consecutive activity fronts (AF) of the migrating motor complex (MMC cycle) and a shorter than normal percent of time occupied by AFs. In normal subjects and in DU2, the administration of the lowest dose of impromidine induced a motor pattern similar to that of the basal period of groups DU and GD, whereas the highest dose disrupted the MMC pattern that was replaced by an irregular motor activity. The results of this study indicate that duodenal ulcer with acid hypersecretion shows a marked inhibition of the MMC cycle that is not due to the ulcer itself, but to the increased acid secretion. In fact, the same motor pattern is observed in other hypersecretory states, both spontaneous and drug-induced, whereas DU with normal secretion showed a near normal motility. In active duodenal ulcer, the decreased incidence and duration of activity fronts may play a role in the pathogenesis of peptide ulcer, as it may impair the cyclic duodenal acid clearing, allowing a longer than normal contact of HCl with the duodenal mucosa.