BACKGROUND It is unclear whether the extent of duodenal gastric metaplasia is due to Helicobacter pylori and/or acid. OBJECTIVE To investigate the role of Helicobacter pylori eradication in the regression of duodenal gastric metaplasia in patients with duodenal ulcer maintained in acid suppression conditions. METHODS . Duodenal (anterior, superior inferior walls of first part of duodenum) and gastric antrum biopsies were obtained from 44 Helicobacter pylori positive duodenal ulcer patients. Helicobacter pylori infection was diagnosed by rapid urease test, histology and 13C-Urea Breath Test. Patients were treated with 20 mg omeprazole tid associated with 250 mg clarithromycin and 500 mg amoxycillin four times daily for 10 days and maintained with 20 mg omeprazole daily for 18 weeks. Control endoscopies were performed at 6 and 18 weeks after beginning treatment. RESULTS Duodenal gastric metaplasia regression was observed in all (32/32) patients in whom Helicobacter pylori was eradicated, but in only 3 out of 6 patients in whom eradication was not achieved (p<0. 001). CONCLUSIONS . The present results suggest that Helicobacter pylori eradication associated with prolonged acid suppression may represent a good therapeutic strategy to achieve duodenal gastric metaplasia regression and highlight the combined role of acid and Helicobacter pylori in the pathogenesis of duodenal gastric metaplasia.