The effect of the C-terminal octapeptide of human oxyntomodulin (KA-8) on pentagastrin-stimulated gastric acid secretion was studied versus placebo in eight human volunteers after an overnight fast, using a double-blind randomized protocol. KA-8 (7.5 nmol/kg body weight) was bolus-injected at a plateau stimulation obtained with pentagastrin (3 micrograms/kg/h). KA-8 significantly decreased the volume secreted by 36% (p less than 0.025) and the acid output by 32% (p less than 0.025) 20 min after injection. The areas under the curve were significantly reduced for volume and acid output during the 1st h after peptide injection.