On the basis of the Osterbro investigation (Copenhagen City Heart Study) which includes several thousand smokers and non-smokers, the authors have analysed the risk of developing chronic mucus hypersecretion and decrease in forced expiration volume in the first second of expiration (FEV1) in the course of a five-year period in the following groups: non-smokers, smokers of cigarettes without filters, smokers of filter cigarettes, smokers of cigarillos/cigars and pipe smokers. All of the types of tobacco investigated led to increased loss of pulmonary function and to increased risk of development of mucus hypersecretion as compared with non-smokers. The differences between the injurious effects of the types of tobacco were limited and were probably due to different inhalation habits in the various groups of smokers. It is concluded that there is no evidence that change from one type of tobacco (eg cigarettes) to another type (eg pipe or cigar tobacco) will reduce the risk of developing chronic obstructive pulmonary disease unless the change is accompanied by considerable reduction of the tobacco consumption.