African-Americans have lower lung function than whites. However, the relative contributions of body habitus and socioeconomic factors are unknown. To address this question, we analyzed data from 1242 white (806 women, 436 men) and 1084 African-American (696 women, 388 men) asymptomatic, nonsmoking adult participants of the third National Health and Nutrition Examination Survey (NHANES III). African-Americans were poorer, had larger FEV(1)/FVC and body mass index (BMI), but lower sitting height, FEV(1) and FVC than whites. Cross-sectional regression analyses using spirometric, anthropometric, and socioeconomic data were performed separately by sex to investigate racial differences in lung function. Sitting height accounted for 35-39% of the race difference in both sexes. Poverty index accounted for about 7.5% and 2.5% of the racial difference in women and men, respectively, whereas the effect of education accounted for about 2% in women and 4.7% in men. With further adjustment for BMI, we could account for only about half of the racial difference in FEV(1) and FVC. We conclude that the racial difference in lung function is only partially explained by a shorter upper body segment in African-Americans. Although low socioeconomic indicators are related to lower lung function, they explain only a small proportion of this racial difference.