In the course of 750 routine duodenoscopies. 119 patients with duodenal ulcers who also had gastric acid tests, were assessed. A relationship was found between the depth of duodenal ulcers and the height of the gastric acid output. In both Black and Indian patients, maximal acid output was significantly higher in patients with deep duodenal ulcers compared with flat duodenal ulcers. There were more Blacks with deep ulcers, and more Indians with flat ulcers.S. Afr. Med. J., 48, 1405 (1974)