After reviewing the more recent acquisitions on the physiology and pathophysiology of gastrin, the authors concentrate on situations of hypergastrinemia, which they divide into a hyperhydrochloric and a hypohydrochloric variety. Among the former, which they subdivide into preoperative and postoperative, the authors discuss problems of differential diagnosis versus peptic ulcers in patients so afflicted. To that end they propose diagnostic policies comprising among other instrumental and laboratory tests the study of gastric secretion, blood gastrin levels in basal conditions and after stimulation by a protein meal, BBS, secretin, and calcium. From analysis of the results of such tests they were able to find a precise nosographic placement for postoperative hypergastrinemia, and from there they arrived at surgical programs aiming to correct postoperative peptic ulcers on the basis of their etiology and pathogenesis.