The aim of the study was to evaluate whether Helicobacter pylori could be involved in the early stages of the severe corpus atrophy that is characteristic of overt pernicious anaemia and is usually H. pylori-negative. The behaviour of H. pylori infection and chronic gastritis was studied in 159 first-degree relatives of pernicious anaemia (PA) probands and was compared with that in 137 first-degree relatives of duodenal ulcer (DU) probands. DU is as a rule associated with H. pylori infection. PA relatives showed a markedly higher prevalence of severe corpus atrophy and of parietal cell antibodies than DU relatives. However, the prevalences of H. pylori did not show significant differences between the two groups of relatives. The age-specific prevalences of H. pylori infection increased similarly in both series of relatives up to geriatric age, together with an increase in the mean scores of corpus gastritis. However, in older age the prevalence of H. pylori in PA relatives showed a marked decrease, in spite of the increase in the mean gastritis score. The present result suggests the possibility that H. pylori is involved in the early PA stages that lead to severe corpus atrophy. The later progress of gastritis seems to be dependent on factors other than H. pylori, most likely 'autoimmune' mechanisms.