To study the prevalence and course of chronic gastritis (CG), 142 adult subjects collected at random from an Estonian urban area were endoscopically and bioptically examined at a six-year interval. The histology of the antral and corpus mucosae was evaluated by grading gastritis without ("superficial gastritis"; SG) and with atrophy ("atrophic gastritis"; AG) into mild, moderate and severe categories. A total of 135 (95%) and 139 (98%) subjects showed CG in the 1st and 2nd examinations, respectively. The CG healed in one subjects (0.7%), and in 5 out of 7 subjects with normal stomach in the 1st examination the CG started during the follow-up. No change in the severity of CG was seen in 24% of subjects with gastritis in the 1st examination. The main trend of CG was a slow, "one-step progression" in severity of inflammation and appearance of atrophy and intestinal metaplasia. Inflammation progressed significantly, especially in the young age groups and in the antrum in particular. The prevalence of AG increased linearly with age in corpus (mean annual risk 1.25%). Parietal cell antibodies (PCA) were found in 2 subjects in the 1st examination, and a further 2 subjects developed these antibodies later. Three of four PCA-positive subjects belonged to a subgroup of 8 elderly subjects who had corpus AG at both examinations and who also showed normal or normalizing mucosa in the antrum. It is concluded that CG is a slowly progressive disease advancing with time and, once started, rarely healing spontaneously.