Gastric secretions contain hydrogen ions at a concentration that is more than one million times higher than their intracellular concentration. This phenomenal gradient as well as the demonstrated ability of gastric juice to digest tissues has motivated clinicians and investigators alike to emphasize acid secretion and acid ablation in studying the pathogenesis and therapy of peptic ulcer disease. Conse- quently, over the past 150 years, we have made considerable progress in under- standing the mechanisms and regulation of acid secretion by the stomach. Not surprisingly, therapy for both...