The influence of long-term cigarette smoking on the pathophysiology of chronic respiratory diseases with obstructive ventilatory dysfunction was discussed in patients with asthma and pulmonary emphysema (PE). 1. In patients with asthma, significant differences in the pathophysiology of the disease were observed between smokers and nonsmokers. A positive RAST score against inhalant allergens, bronchial hyperresponsiveness, and LTB4 generation by leucocytes were significantly more increased in smokers than in nonsmokers. The values of FEV1/FVC and OLco were significantly more decreased, and % RV was significantly more increased in smokers than in nonsmokers. 2. In comparison of asthma with PE, IgE-mediated allergy was significantly more increased in smokers with asthma than in nonsmokers with asthma and in smokers with PE. The values of % FEV1, FEVl %, and % OLco were significantly higher in nonsmokers with asthma than in smokers with PE, however, the % OLco and % RV were not significantly different between smokers with asthma and those with PE. The % LAA of the lungs on HRCT was larger in patients with PE than in smokers and nonsmokers with asthma. The results suggest that cigarette smoking influences the pathophysiology of asthma and PE.