Background : Eradication therapy is recommended for the patients with Helicobacter pylori associated peptic ulcer, because eradication of H. pylori means cure of peptic ulcer disease. The eradication rate of H. pylori can be reached to 80% with PPI based triple therapy in Korea. Drug sensitivity, gastric pH, and compliance are known to affect the eradication rate of H. pylori. In Korea, drug sensitivity has not been studies because of the difficulty of H. pylori culture. It is required that the specific antimicrobial regimens be chosen in consideration of the resistant strains in Korea. Methods : To evaluate the susceptibility of the four antimicrobial agents (such as amoxicillin, tetracyclin, metronidazole, and clarithromycin) to H. pylori, and to determine the retreatment drugs for the patient who failed to initial eradication therapy, prospectively we evaluated 47 patients (23 duodenal ulcer, 11 gastric ulcer, 13 chronic gastritis). Upper endoscopy was performed in al1 patients, and H. pylori was cultured in blood agar plate included Claxo selective supplement A and drug sensitivity test was performed. Results : The results were as follows: 1) Overall culture rate of H. pylori was achieved in 47 of 80 patients (58.8%). 2) The bactericidal activity of amoxicillin, tetracyclin, metronidazole, and clarithromycin was 91.5%, 76.6%, 53.2%, and 76.6%, respectively. 3) The three strains (6.4%) were showed resistant to all four antibiotics. Conclusion : In Korea, amoxicillin resistant strains were identified for the first time, clarithromycin and metronidazole resistant strains were more frequent than in other developed countries.