Since the mid-seventies, it is possible to treat peptic ulcers and reflux oesophagitis with acid secretion inhibitors. The most important medicaments are H2-receptor antagonists (cimetidine was registered in 1977) and proton pump inhibitors (1988: omeprazole). Surgical treatment of these conditions is almost a thing of the past. Many Dutch researchers played an important part in clinical research of acid secretion inhibitors; the first studies of effect and safety were done in patients with severe overproduction of gastric acid (Zollinger-Ellison syndrome) and in those with severe reflux oesophagitis. At present the most important syndromes in which acid secretion inhibitors are used are gastroesophageal reflux disease, gastric or duodenal ulcers and acid-related dyspepsia.