In order to understand the relation between the prevalence of Campylobacter pylori and the severity of gastritis, we conducted a survey of 166 randomly selected dyspeptic patients. The presence of C. pylori on the antral mucosa was aseptically determined by both urease and bacterial culture tests. Specimens of antral mucosa were obtained for pathologic gradings of inflammation: active gastritis, mononuclear cell infiltration C0 (nil) to C3 (lymphoid follicle); presence or absence of intestinal metaplasia. Pathologically, chronic gastritis was invariably present in almost all patients with dyspepsia: three-fourths of them showed evidence of active gastritis, one-third showed intestinal metaplasia. Half of the dyspeptic individuals had C. pylori colonization. The results suggest that the prevalence of C. pylori was closely related to the different grades of active gastritis; neither the different grades of chronic gastritis nor intestinal metaplasia affected the prevalence of C. pylori on gastric mucosa. We conclude from this study that C. pylori is closely related to active chronic gastritis because of the common presence of chronic gastritis in patients with dyspepsia.