The effect of i.v. pirenzepine infusion both on basal and pentagastrin and insulin-stimulated secretion was studied in 19 healthy and duodenal ulcer subjects. Following an overnight fast, gastric juice was collected for 30 minutes prior to the i.v. administration of pirenzepine (16 mg plus 2 mg/h for 2 hours) and the subsequent stimulation of gastric secretion by means of i.v. pentagastrin infusion (6 microgram/kg/h) or i.v. insulin injection (0.2 U/kg). Mean acid output was reduced--in comparison to placebo--by 22% after pentagastrin stimulation and by 34% after insulin stimulation.