Histoautoradiographic procedures were employed to establish the level of cell proliferation in gastric epithelium, using biopsy material from 84 patients suffering from gastritis--59 cases (superficial)--10, glandular lesions other than atrophy--18, mild atrophy--13, moderate atrophy--11, severe atrophy--7), 17 cases of peptic ulcer and 8 patients with adenomatous polyposis. Cell proliferation level in patients with peptic ulcer and polyps was identical to those in cases of non-atrophic gastritis or mild atrophy of mucosa. In cases of gastritis, the rise in cell proliferation is matched by the advancement of atrophic changes and reaches its peak in patients with severe atrophic gastritis. It is suggested that chronic gastritis involving pronounced atrophy of mucosa constitutes the most important factor of risk of cancer among the other precancerous lesions of the stomach.