PURPOSE:The purpose of this study is to assess the pulmonary airway reactivity in asthmatic patients directly and noninvasively by using high-resolution CT(HRCT). MATERIALS AND METHODS: 130 bronchial luminal areas were measured by HRCT in 16 asthmatic patients before and after inhalation of bronchodilator (Salbutamol sulfate). The change of bronchial luminal area on HRCT was analyzed and correlated with the change of forced expiratory volume in 1 second(FEV1) on pulmonary function test in each patient. RESULTS: The mean percentage of increase in luminal areas of the 130 bronchi after bronchodilator inhalation was 95.4 +/- 103.3%. The group with the smallest luminal areas (lesser than 1.35mm2) was more sensitively increased in area than the group with the largest areas (equal or larger than 3.72 mm2) ;183.5% versus 63.5%. The mean percentage of increase in FEV1 was 21.7% and there was no statistically significant correlation between the increased degrees of luminal areas and that of FEV1(r=-0.04). CONCLUSION:We can measure the bronchial luminal area directly and noninvasively with HRCT and can also estimate the degree of airway reactivity in asthmatic patient by measuring of the changes of bronchial luminal areas after administration of bronchodilator.