The effect of 2 hours' intravenous infusion (7.5 mg/h) of propantheline bromide (Ercotina, Erco Läkemedel AB) on basal or pentagastrin-stimulated gastric secretion was studied in 7 healthy subjects and in 11 patients with acute duodenal ulcer. A moderate to marked decrease in acid secretion rate and acid output was found both in subjects and patients during the infusion period. The acidity decreased in most of the subjects but did not change much in the patients. Two other dose rates (3.75 and 15 mg/h) were studied in a few subjects and patients. The lowest dose rate gave as good an inhibition of the gastric secretion as the higher ones. No troublesome side effects were noticed. It was concluded that a dose rate of around 5-10 mg/h may be suitable for prolonged i.v. infusion, for example as trial therapy in patients with upper gastro-intestinal bleeding.