Sydney system in the classfication of histologic gastritis recommends the grading of Helicobacter(H.) pylori density, activity and chronic inflammation. CLO test is a rapid urease test to diagnose H. pylori infection. The relation between the grading of gastritis and the positivity of the CLO test has not been well studied. Accordingly, this study was performed to investigate the positive rate of the CLO test according to the grade of gastritis.

One hundred consecutive endoscopy patients had two antral biopsies for CLO test and histopathologic examination. H. pylori density, activity and inflammation were each graded into 0, 1, 2, and 3.

1) CLO test was positive in 52 among 100 cases(52%) and among the CLO test positive cases, forty five(86.5%) became positive within 1 hour.

2) The positive rate of the CLO test increased according to the grade of H. pylori density, mucosal activity and chronic inflammation.

3) The group(n=45) who turned positive within 1 hour showed higher grade of H. pylori density than the group(n=7) who turned positive from 1 to 24 hour.

It was thought that the grade of histologic gastritis reflected the positive rate of the CLO test and reaction time to a positive CLO test is related to H. pylori density.