Dragstedt believed that basal hypersecretion of gastric acid was the root cause of duodenal ulcer, that the hypersecretion was due to an increased vagal stimulation, and that vagotomy would therefore cure duodenal ulcer. He introduced vagotomy and demonstrated that the operation was successful in curing most patients of their duodenal ulcers. This article reviews how further research in the succeeding half century has demonstrated that it is the effect of vagotomy on stimulated, rather than upon basal secretion that cures duodenal ulcer and that the apparent basal hypersecretion of patients with duodenal ulcer is due to an increased parietal cell mass. The article points out that there is no convincing explanation as yet of the mechanism whereby vagotomy reduces histamine-stimulated gastric secretion.