Objectives: Many studies about the role of H. pylori on the gastritis, duodenal ulcer, benign gastric ulcer and stomach cancer have been carried out actively and many test methods of detecting H. Pylori have been developed. However, few studies have been reported about the sensitivity or applicability of these test methods and it can be seen that little consideration was taken into the sensitivity of these methods in some papers. This study was done to evaluate the sensitivity of each test method for identifying H. pylori infection and to evaluate time distribution of positive response in the CLO test. Methods: Four different test methods for identifying H. Pylori infection - Gram stain of touch print, CLO test, culture, H&E stain were taken in the 280 patients with duodenal ulcer. The sensitivity of each test was evaluated for the 264 H. pylari positive cases and positive time in the CLO test was measured. Results: 1) All four tests were positive in 80 cases (30.3%), three tests or more were positive in 197 cases (74.7%), and two tests or more were positive in 241 cases (91.3%). 2) There were 23 cases (8.7%) indicating H. pylori positive according to only one test, of which 15 cases (5.7%) were positive according to Gram stain and 8 cases (3.0%) according to CLO test, Either Gram stain or CLO test was positive in 100% of 264 H. pylori positive cases. 3) The sensitivity of Gram stain of touch print was 94.7%, that of CLO test 90.5% and that of H&E stain 69.3%, which was significantly lower than that of Gram stain or CLO test. The sensitivity of culture was 40.2% and it was significantly lower than that of H4E stain. 4) The positivie rate of Gram stain in the 106 culture positive cases was 100% (106 cases) and that of CLO test and H8rE stain were 93.4% (99 cases) and 77.4% (82 cases), respectively. 5) Of the 239 positive CLO tests, 129 cases (54.0%) indicated H. pylori positive within 20 min, 204 cases (85.4%), 231 cases (96.7%) and 239 cases (100%) within 1 hr, 3 hrs and 24 hrs, respectively. 6) Of the 99 culture and CLO test positive cases, 62 cases (62.6%) indicated H. pylori positive within 20 min in CLO test, and 87 cases (87.9%), 93 cases (93.95%) and 99 cases (100%) within 1 hr, 3 hrs and 24 hrs, respectively. Conclusion: From these results, we can conclude that the most sensitive test in detecting H. pylori is the Gram stain of touch print, and the next is CLO test. Just these two tests enable us to determine H. Pylori infection for almost all patients, this signifies that these two tests, not all of the four tests, are sufficient for H. pylori infection test. In the CLO test, 96.7% of the positive cases were diagnosed to be positive within 3 hrs, so that CLO test is considered to be a very speedy test in the diagnosis of H. pylori infection.