Among intrinsic factors which may affect the onset of COPD, bronchial non specific hyperresponsiveness seems to play an important, even though, ill-defined role. Attention is drawn to 2 major points: 1) Cigarette smoking habit may increase airway responsiveness? 2) Any possible hyperresponsiveness induced by smoking may be relevant in the development of COPD? At present, only point 1 may be positively answered; point 2 will be clarified by means of perspective and long-term surveys, we have not achieved yet. Our cross-sectional study showed a significant influence of smoking on bronchial responsiveness in absolutely asymptomatic subjects and with airway caliber absolutely in the normal range. This kind of influence resulted to be dose-dependent. Furthermore a noxious role of smoking has been observed, the greater effect the higher amount of cigarettes/day smoked. Moreover this acute role of smoking has been remarked by the trend of bronchial responsiveness of past-smokers, the more similar to non smoker's, the more far was smoking cessation.