In this study, we tried to evaluate the usefulness of Superoxide Dismutase (SOD) activity in detecting gastric cancer. SOD was determined according to M. Minami and H. Yoshikawa, a simple and inexpensive assay method. For 11 fibrogastroscopy and pathological proved gastric cancer cases, the average levels of SOD activity was found significantly lower than 30 patients with gastric diseases, 8 patients with atypical hyperplasia and 32 controls.