Helicobacter pylori infection is commoner in black and Hispanic people compared with age matched white people. H pylori status was evaluated using an enzyme linked immunosorbent assay for anti-H pylori IgG in 150 healthy black and Hispanic people aged between 19 and 49 years. All were employed and had completed high school at least. Socioeconomic status during childhood was estimated from the parents' education and occupation(s) using a modified Hollingshead index and family income. Five social classes were defined (class I = lowest, V = highest). The H pylori prevalence was inversely related to the social class during childhood. It was 85% for class I, 52% for combined classes II and III, and 11% for classes IV and V combined. The inverse correlation remained after adjustments were made for the present social class and age. H pylori infection was also related to crowded living conditions (odds ratio 4.5: 95% confidence interval 3.3, 5.7) for those who had had the most crowded living conditions during childhood). The increased prevalence of H pylori in black and Hispanic people seems to be related to low socioeconomic status in childhood. These data are also consistent with the suggestion that childhood is a period of major risk for H pylori infection.