From many findings, it has been established that persistent infection of Helicobacter pylori (H. pylori) causes chronic active gastritis and subsequently causes the gastric mucosa of the high risk for gastric cancer development. On the other hand, recent Japanese-study results have shown the possibility of gastric cancer prevention by H. pylor eradication. Moreover the development of gastric cancer in uninfected subjects is very rare; therefore, prevention of gastric cancer by H. pylori eradication becomes a topic in Japan. To get rid of gastric cancer from Japan, the risk of gastric cancer should be determined by presence of H. pylori infection in a young fellow, on the other hand, the risk by the examination that combined serum PG method with serum antibody method in subjects after middle aged. It is now expected that eradication treatment should be performed for these high-risk subjects.