IN view of the role of gastrin as a potent gastric secretagogue, the established gastric hypersecretion in subjects with duodenal ulcer (DU), and the much increased tendency to gastrointestinal ulceration in patients harboring a gastrin-producing tumor (Zollinger-Ellison syndrome), an appraisal of the status of gastrin secretion in DU patients is clearly of some importance. The recent availability of radioimmunoassays for plasma gastrin now permits such an evaluation. The relation between the rate of secretion of a hormone and the concentration of its target substance in body fluids can usually be depicted in the form of a closed loop in which . . .