Background/Aims: The aim of this study is to determine the incidence of vacuolating cytotoxin-producing Helicobacter pylori(HP) in patients with gastritis, peptic ulcer and gastric cancer. Methods: Gastric mucosa was sampled during gastric resection or gastric endoscopy. The biopsy specimens were ground with glass tissue homogenizer and inoculated on Brain Heart infusion blood agar supplemented with 5% fetal calf serum and selective supplements(Oxoid, England) and to the Christensen urea broth for urease test. Vacuolating cytotoxin assay was done using RK-13 cells as target and vacuolating cytoxin-producing HP TK 1023, TK 1029, KR 2008, KR 2069 (Prof. Kamiya S, Kyorin University School of Medicine, Tokyo, japan) as standard according to the method of Kamiya. Results: Rates of positive culture of HP in gastric mucosa of gastritis cases was 50.5%, peptic ulcers 61.5%, and gastric carcinoma 42.5%. The percentage of vacuolating cytotoxin-production of HP in gastritis group was 81.4%, 75% in peptic ulcers, and 86.7% in gastric carcinoma cases. Conclusions: With the above results we can conclude that there was no difference in the rates of positive culture of HP in cases of gastritis, peptic ulcer and gastric carcinoma. There were no significant differences in the incidences of cytotoxin-producing KP in cases of gastritis, peptic ulcer and gastric carcinoma in this study. (Korean J Gastroenterol 1997; 30:454-461)