The present study intended to investigate the effect of antroduodenal acidification on gastric acid secretion and emptying, gastrin and somatostatin release in response to food in healthy subjects as well as in duodenal ulcer patients. Ten duodenal ulcer patients and 9 normal controls were studied twice: the same 400 ml liquid protein meal (proteins: 10 g) was introduced into the stomach; then intragastric pH was either maintained at pH 4.5 or allowed to decrease in response to the meal. Acid secretion was calculated using the intragastric titration method (for which the intragastric pH is fixed at pH 4.5) and using the serial dilution indicator method (which allows antral acidification) respectively. Gastric emptying was estimated according to: a) iterative measurements of intragastric meal residual volume; b) volume passing through the pylorus. These two tests were performed in a random order and during each, plasma gastrin and somatostatin responses to the meal were determined. In healthy subjects, antral acidification following the meal was associated with a significantly lower acid secretion (17.3 +/- 0.9 mmol/h; m +/- SEM) than when the pH was maintained at pH 4.5 (20.2 +/- 1.3; p less than 0.05). Moreover, gastric emptying was slower when the pH was allowed to decrease (t 1/2: 26.2 +/- 1.4 min) than when the pH was constant (t 1/2: 20.5 +/- 2.2 min; p less than 0.05). By contrast, in the duodenal ulcer group, neither acid output nor gastric emptying were significantly different in the two situations.(ABSTRACT TRUNCATED AT 250 WORDS)