Seventeen lifetime nonsmoking male teachers and 17 smoking male teachers with normal lung function were compared. The smokers showed a significantly greater prevalence of cough (p < 0.01), sputum production (p < 0.05), and wheezing (p < 0.01), but not dyspnea. There was no difference in the prevalence of a history of allergy, or the number of positive reactions to allergy prick skin tests, or in elevated serum IgE. Lung volumes, expiratory flow rates, specific airway conductance (SGaw), and the slope of phase III of the single breath O2 test were not significantly different. The geometric mean provocation concentration of histamine required to reduce the SGaw by 35% (PC35) was significantly lower in the smokers (1.84 mg/ml) than in the nonsmokers (4.83 mg/ml) (p < 0.005). Increased nonspecific bronchial reactivity may be a factor contributing to the development of airway obstruction in smokers.