Seventy-four patients with duodenal ulcer were followed up longitudinally for 2 years after initial ulcer healing. Endoscopy including biopsy of the antral mucosa was performed every 3rd month and whenever clinical symptoms of relapse occurred. The presence of Helicobacter pylori in the biopsy specimens was scored as 0 (none), 1 (sporadic occurrence), 2 (clusters), and 3 (numerous bacteria found diffusely in the mucus layer). The incidence rates of ulcer relapse per patient-month, grouped in accordance with these scores, were (with 95% confidence intervals) 0.073 (0.048-0.111), 0.083 (0.052-0.133), 0.123 (0.096-0.157), and 0.069 (0.041-0.116), respectively. No significant differences in incidence rates across H. pylori scores were observed when taking into account the observation period after healing of the first ulcer, number of ulcer recurrence (1st, 2nd, 3rd), sex, age, smoking habits, peak acid output, time of healing of the preceding ulcer, treatment of the present ulcer (cimetidine, antacids, or no treatment), or type and degree of gastritis. Thus, although H. pylori is prevalent in patients with duodenal ulcer disease, the present study indicates that H. pylori does not have a substantial note in the precipitation of active duodenal ulcer.