A survey for the prevalence of chronic bronchitis in an industrial population in North India is reported. The prevalence of chronic bronchitis is 12.5 percent in 473 subjects between the ages of 17 and 64 years. The prevalence rate of chronic bronchitis is comparable to that observed in areas of low community air pollution in Europe and North America. There is no age-related rise in the frequency of respiratory symptoms. The consumption of tobacco in these subjects is low and is comparable to tobacco consumption of light smokers. The prevalence of chronic bronchitis in smokers is five times the prevalence in non-smokers and is similar to the values reported for light smokers in other surveys. These observations suggest that cigarette smoking is associated with the development of chronic bronchitis, and the differences in the prevalence rate of chronic bronchitis between this survey and other surveys conducted in Europe and North America are mainly due to differences in smoking habits. Air pollution has a minor effect only and ethnic differences do not appear to play any part. Forced expired volume in one second shows a negative correlation with age. It is lower in asymptomatic smokers than in non-smokers and is lower in chronic bronchitis than in controls.