Helicobacter pylori is known to be responsible for most cases of chronic gastritis, but its role in the outcome of gastric ulcer is unknown. The purpose of this study was to determine the prevalence of H. pylori infection before and after treatment of gastric ulcer, the micro-organism being untreated. The trial involved 26 patients with an acute episode of gastric ulcer, who had undergone endoscopy with biopsy of the antrum, the fundus and the ulcer rim at the initial examination and then 6 weeks and 1 year after the diagnosis. At day 0, 25 acute ulcers were associated with chronic H. pylori gastritis; one patient had neither gastritis nor H. pylori infection. The H. pylori count correlated with the activity of chronic gastritis and with the extension of intestinal metaplasia; it was not modified by the healing of gastric ulcer observed in 24/26 patients on day 360. These results confirm the existence of a close association between H. pylori, chronic gastritis and gastric ulcer. It also suggests that H. pylori is not directly involved in the healing or recurrence of gastric ulcer.