"Anyone who claims to have discovered the ideal procedure in the treatment of gastric ulcer, should be considered immodest." These words by Schnitzler (1914) are in principle still valid. The pathogenesis and operative procedure are not identical. There is still no conclusive proof of the pathogenesis. The disclosure of other pathogenetic factors and facts is gradual. Locally active chemical noxae (e.g., propionitril) are responsible for the development of duodenal ulcer. Gastric ulcer is caused by the reflux of duodenal juice (e.g., lysolecithin, which is capable of corroding the mucosal barrier of the stomach. The current pathogenetic mechanisms of ulcer of the usual locations are specified.