Influence of long-term clgarette smoking on the paphophysiological changes of the disease was compared between younger and older patients with asthma. 1. The frequency of positive RAST score against inhalant allergens was significantly higher in ex-smokers than in never-smokers in older patients with astham, but not in younger subjects. 2. Ventilatory parameters such as % FVC and FEV 1.0% were not sig-nificantly different between ex-smokers and never-smokers either in younger or older patients, although a significant difference in these values was observed between younger and older subjects. 3. The % DLco was significantly lower in ex-smokers than in never-smokers both in yonger and older patients. 4. The parameters associated with hyperinflation asuch as % RV and % LAA of the lungs on HRCT were significantly higher in older patients than in younger subjects, and also significantly larger in ex-smokers than in never-smokers in older patients, but % RV was not different between ex-smokers and never-smokers in young subjects. 5. Bronchial hyperresponsiveness (BH) was significantly more increased in ex-smokers than in never-smokers in older patients, but not in younger subjects. There was a significant difference in BH be-tween younger and older patients. 6. LTB4 generation was significantly larger in ex-smokers than in never-smokers in older patients, and LTC4 generation was more in-creased in ex-smokers both in younger and older subjects. The results show that significant differences between ex-smokers and never-smokers were observed in % DLco, LTC4 generation and % LAA both in younger and older subjects, and in IgE an-tibodies production, % RV, BH and LTB4 generation only in older subjects. In contrast, the values of % FVC and FEV1.0% were not different between ex-smokers and never-smok-ers either in younger or older subjects. A significant difference between younger and older subjects was found in all other parameters except % DLco and LTC4 generation.