To investigate the frequency of use of nonsteroidal anti-inflammatory drugs (NSAID) in duodenal or pyloric ulcer patients who do not have Helicobαcter pylori gastritis, we retrospectively analyzed the use of these drugs among 16 patients who had an endoscopically diagnosed duodenal or pyloric ulcer but had a histologically normal and noninfected stomach, and compared this frequency of use of NSAIDs with that in three control groups. The 16 patients are a consecutive subgroup (2.3%) from 707 patients who were endoscopically diagnosed as having duodenal or pyloric ulcer in Jorvi Hospital during 1985– 1994. In all 16 patients, endoscopical and clinical appearances of the ulcers were seen by the clinician similar to those in ordinary peptic ulcer disease. The ulcers occurred at the same site in the duodenal bulb and pylorus as the ordinary peptic ulcers but tended to bleed more often: endoscopy was done more frequently among the 16 gastritis-negative patients because of ulcer bleeding than among the controls. Thirteen of the 16 patients (81%; CI95: 62-100%) did use NSAIDs. This frequency was higher (p < 0.05) than the corresponding frequency of the use of NSAIDs in any of the three control groups, i.e (a) H pylori-positive duodenal or pyloric ulcer patients [16 of 39 (41 %)], (b) H pylori-negative nonulcer patients [11 of 64 (17%)] or (c) H pylori-positive nonulcer patients [14 of 42 (33%)]. We conclude that the history of use of NSAIDs is more common in duodenal and pyloric ulcer patients who have a normal, noninfected stomach than the history of use of NSAIDs in those in whom the ulcer is associated with H pylori gastritis.