Hyperpepsinogenaemia has long been considered an important factor in the pathophysiology of duodenal ulcer. Moreover, H. pylori infection has been reported in virtually all duodenal ulcers. OBJECTIVE. To demonstrate the influence of H. pylori eradication on basal pepsinogen I levels in patients with duodenal ulcer. METHODS. 86 patients with endoscopically proven duodenal ulcer were prospectively studied. Different therapeutic regimens were used: Amoxycillin/clavulanate plus omeprazole or ranitidine, triple therapy, omeprazole and ranitidine. At diagnostic endoscopy and after therapy, three biopsy samples were taken from different levels and analyzed by microbiological and histological methods; also, basal pepsinogen I levels were measured. RESULTS. H pylori eradication was associated with a significant histological improvement (p < 0.001), both in gastric antrum and corpus. In patients where H. pylori was eradicated pepsinogen I levels decreased from 107.6 +/- 31 ng/ml to 79.7 +/- 32 ng/ml after therapy (p < 0.001); however, when eradication was not achieved differences were not significant. CONCLUSION. H pylori eradication in patients with duodenal ulcer was associated with a significant decrease in basal pepsinogen I levels. The verification of such a decrease could represent a useful non-invasive method to monitor the efficiency of therapy, both in H. pylori eradication and in the resolution of the associated gastritis. This procedure is also associated with early results and a low cost.