The percentage of attenuation area < -950HU (% LAA) on high resolution computed tomography (HRCT) was compared between 17 smoking and 24 nonsmoking patients with asthma. 1. FEV1/FVC value was lower in smoking patients (56.4%) than in nonsmoking patients (66.0%), however, the difference was not significant. 2. The percentage of LAA of the lung was larger in smoking patients compared with that in nonsmoking patients in all the three anatomic levels: the % LAA was 14.4% in nonsmoking and 20.3% in smoking patients at lower lung level (3cm above the top of the diaphragm). However, this was not significant. The maximal % LAA among the three lung levels on HRCT was 21.6±12.5% in smoking, and 15.7±11.9% in nonsmoking patients. This suggested that the maximal % LAA was larger in smoking patients, however, this was not significant. 3. The mean CT number of the lung on HRCT was smaller in smoking patients (-897.3HU) than in nonsmoking patients (-884.7HU). 4. Three of 4 nonsmoking patients whose % LAA was more than 30% had severe intractable asthma with long-term glucocorticoid therapy. The results suggest the possibility that smoking influences the % LAA of the lung on HRCT in asthma. It could be also speculated that % LAA is influenced by severity of asthma.