Helicobacter pylori and associated duodenal ulcer. Twenty three children with coexistent duodenal ulcer and Helicobacter pylori infection were treated with either two weeks of amoxycillin (25 mg/kg/day) in addition to six weeks of cimetidine, or cimetidine alone. Endoscopy with antral and duodenal biopsies for urease test, microaerophilic culture, and histological studies were performed at entry, six weeks, 12 weeks, and at six months. Children with persistent H pylori infection at six weeks were given a further two weeks' course of amoxycillin. H pylori persisted in all children not receiving amoxycillin treatment but cleared in six of the 13 children (46%) treated with amoxycillin. With failure of H pylori clearance at six months, only two out of six (33%) ulcers had healed and 50% of patients had experienced ulcer recurrence. In contrast, when H pylori remained cleared all ulcers healed and no ulcer recurred. Persistent H pylori infection was associated with persistent gastritis and duodenitis despite endoscopic evidence of ulcer healing. Detection and eradication of H pylori deserves particular attention in the routine management of duodenal ulceration in children. 