Gastric atrophy and intestinal metaplasia are considered the earliest phenotypic changes in the cascade of events leading from normal mucosa to intestinal-type gastric cancer, and epidemiological evidence links Helicobacter pylori to gastric epithelial malignancies. To evaluate any causal relationship between bacterial infection and atrophic metaplastic lesions, gastric pathology was histologically and histochemically evaluated in 267 consecutive, nonulcerous, untreated subjects, with attention given the phenotypes of intestinal metaplasia. The prevalence of Helicobacter pylori infection was 61%. Intestinal metaplasia (particularly types II and III) was significantly associated with both Helicobacter pylori detection (chi 2 LR: P < 0.002) and increasing age (chi 2 LR: P < 0.002). Using logistic regression analysis, the development of intestinal metaplasia proved more significantly linked with Helicobacter pylori infection [odds ratio = 4.55 (95% confidence interval: 1.51-13.7)], than with age [odds ratio = 1.03 (95% CI: 1.01-1.06)], with no interaction. In conclusion, Helicobacter pylori can be considered among the major causal agents of mucosal lesions involved in the multistep process of gastric carcinogenesis, justifying any attempt to eradicate this bacterial infection.