Gastric biopsies from 1477 participants in a chemoprevention trial for precancerous lesions of the stomach in Venezuela were evaluated for the prevalence of precancerous lesions and Helicobacter pylori infection. These study subjects were selected from participants in an early detection program for gastric cancer using double-contrast X-ray. Overall, 94% had some type of chronic gastritis (CG) and were positive for H. pylori using Giemsa stain, 49% had atrophic gastritis, 34% had intestinal metaplasia (IM), and 6.5% had dysplasia. There were only three subjects (0.2%) with normal gastric mucosa, and 4% had only superficial gastritis. The prevalence of all of these precancerous lesions increased with age, but there was no clear difference by gender. The prevalence of the various lesions was higher in the antral mucosa than in the fundic mucosa. H. pylori infection was strikingly frequent in our study population, with prevalence rates ranging from 73% in subjects with superficial gastritis to 95% in those with atrophic gastritis and IM and 98% in those with CG. The prevalence of H. pylori was equally high in males and females, and it was significantly positively associated with the degree of infiltration of poly- and mononuclear cells and with that of active regeneration; it was inversely correlated with the degree of atrophy, IM, and dysplasia. Our findings support the precancerous nature of the various gastric lesions and the etiological role of H. pylori infection in CG.