As part of an ongoing study of cardiopulmonary risk factors in the People's Republic of China, we conducted lung function tests and obtained information about smoking habits on 6,765 Chinese men and women 35 to 56 yr of age residing in or around Beijing in the north and in or around Guangzhou in the south. Within each region, separate urban and rural populations were recruited. This study examined the relationship between tobacco consumption (both manufactured cigarettes and leaf tobacco) and lung function in a subset of current smokers and never smokers who had acceptable lung function data. All methods were strictly standardized. Overall, tobacco smoking was associated with a statistically significant mean difference in FEV1 among men (-89 ml) and women (-52 ml) relative to never smokers after adjusting for age, height, and residence. Differences between smokers of cigarettes and smokers of leaf tobacco were not significant. Among the subset of smokers who smoked only cigarettes, this decrement increased with increasing duration of cigarette smoking, but it was small (-4 ml/yr of smoking for FEV1 for both men and women) in comparison with the effects of smoking reported from western countries. Although the smoking effect tended to increase with increasing dose, these differences were small and generally not statistically significant. The relatively small smoking effect in this study may result from differences between developed and developing countries in the cumulative dose of tobacco products. Alternative explanations or contributing factors such as racial differences in susceptibility and differences in the form and delivery of tobacco cannot be discounted.