We report the findings of a cross-sectional study of the relationship between passive smoking and pulmonary function of children in Shanghai, People's Republic of China. The 571 study subjects included 303 males and 268 females, ranging in age from 8 to 16 years, from a primary school and a secondary school at Xu-Hui District. Lung function tests were performed at the schools, and questionnaires were completed by parents. The father's cigarette smoking status during child's lifetime was linearly related to a decrease in the per cent predicted values of FEV1.0, MMEF and FEF 62.5-87.5% in total subjects; in school-girls, father's smoking status accounted for 0.5 per cent, 1.2 per cent, and 1.6 per cent of the total variation, respectively; the trend was less marked in boys. Other environmental factors considered in this study, i.e., educational level of the father, the use of coal or gas for cooking, the presence of patients with chronic respiratory diseases in the family, etc., did not seem to have any important role on the children's pulmonary function.