Relations of Helicobacter pylori (H. pylori) infection to gastric carcinogenesis and histopathology of cancer lesions were examined in comparison with gastric ulcer. Infection of H. pylori was determined by anti-H. pylori IgG antibody in sera. The antibody was found in 19 (61.3 %) of 31 cancer patients and 20 (74.1 %) of 27 ulcer patients. No significant difference was found between cancer and ulcer patients. Concerning the histopathology, no significant difference between the patients with and without antibody was found in any histopathological findings. Urease activity showing H. pylori infection around the cancer lesions did not also affect any histopathological findings. Thus, we reach no clear evidence as to the relation between H. pylori infection and carcinogenesis. Furthermore, the infection may not reveal any effect on the histopathological findings of cancer lesions.