Bronchial reactivity to cigarette smoke (CBR) in a cross-section of 98 smokers has been investigated. All participants were subjects to skin-prick tests to common allergens, lung function measurements and bronchial challenges with methacholine and cigarette smoke. In 38 participants a rechallenge with cigarettes was performed 1 h after the first cigarette challenge. Lung function indices analysed were: forced expiratory volume in one second (FEV1); maximal expiratory flow at 75% of the forced vital capacity (MEF75%); and forced mid-expiratory flow between 25 and 75% of the forced vital capacity (FEF(25-75%)). All participants were tested for asthma and allergy, and were required to provide information regarding respiratory symptoms, first degree relatives with asthma and allergy and smoking habits. A substantial decrease was seen in all lung function indices after 12 cigarette-smoke inhalations, but only FEV1 was related to other variables. The maximal mean percentage fall in FEV1 was 10%, which was directly related to the number of inhalations (p<0.05). In multiple regression analyses the percentage fall in FEV1 was directly related to: FEV1/vital capacity (VC) (p<0.01); to the asthmatic/bronchitic status (p<0.05); and to the accumulated and standardized cigarette consumption (p<0.05). The percentage fall in FEV1 bore no relationship to methacholine bronchial reactivity, sex or age and had a continuous distribution. The repeat challenge showed a smaller fall in FEV1 compared to the first challenge after 12 cigarette smoke inhalations (p<0.05). The percentage fall in FEV1 correlated after the first and the repeat challenge (p<0.05). Repeatability of the challenge could not be determined in this study because of tachyphylaxis. Bronchial reactivity to cigarette smoke is a tobacco smoke-specific bronchial response. All participants responded and the response showed a continuous distribution. Bronchial reactivity to cigarette smoke may be of importance for symptoms and prognosis in chronic bronchitis and chronic obstructive pulmonary disease and should be studied in relation to the degree of accelerated lung function loss in smokers and other cigarette induced lung abnormalities.