We investigated the efficacy of antimicrobial drugs, amoxicillin and clarithromycin that have the in vitro activity against H. pylori, and observed a long term course of ulcer after eradication. The eradication rate of combination therapy with PPI and amoxicillin showed best result (13/18: 72%). In eradicated cases, index of PAS positive substance and gastritis score in antral mucosa that is histological examination was improved, and ammonia concentration in gastric secretions decreased. The recurrent rate of ulcer in long term course after eradication was investigated, the recurrent rate of ulcer was significantly lower in H pylori eradicated cases than in H. pylori continuously positive cases. Results suggest that eradication of H. pylori may be controlled recurrence of H. pylori positive peptic ulcer.