After a brief history of gastroduodenal ulcer since the 19th century, the authors discuss the question of its uniqueness. Upon clinical, biological and genetic grounds, it seems possible to distinguish two different kinds of ulcers. Ulcers situated above the junction between fundic and antropyloric mucosae could possibly be the consequence of biliary reflux, while ulcers situated below this junction would be associated with hyperchlorhydria. Some properties of gastrin, which is responsible for Zollinger-Ellison syndromes I and II, are cited. Presently, gastrin cannot be considered as the primary cause of duodenal ulcer.