African-American children have lower lung volumes than White children. However, the contributions of anthropometric, socioeconomic, nutritional, and environmental factors to this difference are unknown. From participants in the Third National Health and Nutrition Examination Survey (1988-1994), the authors selected 1,462 healthy nonsmoking children (623 White and 839 African-American) aged 8-17 years. The African-American children were taller and heavier but had lower lung function. African Americans were poorer and had lower levels of the antioxidant vitamins A and C and alpha-carotene. The authors performed regression analyses using data on anthropometric, socioeconomic, and nutritional factors and smoke exposure. Adjustment for sitting height explained 42-53% of the racial difference. Socioeconomic factors and antioxidant vitamin levels accounted for an additional 7-10%. Overall, the authors could account for only 50-63% of the racial difference. Exposure to tobacco in the home was weakly associated with forced expiratory volume in 1 second in girls, accounting for 1% of the difference. In children aged 8-12 years (n = 752), birth weight explained 3-5% of the racial difference, whereas in-utero exposure to maternal smoking had no significant effect. The authors conclude that in healthy children, the major explanatory variable for the racial difference in lung function is body habitus; socioeconomic, nutritional, and environmental confounders play a smaller role.