BACKGROUND: Measurement of bronchodilator response is necessary to establish reversibility of airflow obstruction that was helpful to estimate the diagnosis, treatment, and prognosis in obstructive airway disease. An useful index should be able to detect the bronchodilator response more sensitively not related with degree of airflow obstruction and also be independent of initial FEV1. METHOD: Sensitivities of bronchodilator response in each group classified by degree of airflow obstruction in FEV1, FVC, FEF25~75%, Isovolume FEF25~75%, sGaw were studied and correlation coefficients were calculated between initial FEV1 and reversibilities expressed as absolute, %initial, %predicted, %possible in FEV1. RESULT: Sensitivities of bronchodilator response were 61.5% in FVC, Isovolume FEF25~75% and sGaw, in severe group, and 56.3% in Isovolume FEF25~75% and sGaw, in moderate group, and 62.5% in FEV1 and sGaw and 50.0% in FVC and Isovolume FEF25~75%, in mild group, and 60.0% in sGaw and 58.0% in Isovolume FEF25~75% in total patients. Correlation coefficients between initial FEV1(L) and absolute, % initial, % predicted, % possible were 0.15, -0.22(p<0.05), 0.02, 0.24(p<0.05) and correlation coefficients between initial FEV1(% predicted) and absolute, % initial, % predicted, %possible were 0.06, -0.28(p<0.05), 0.08, 0.39(p <0.05). CONCLUSION: Volume related parameters were more sensitive index not related with degree of airway obstruction and the change in FEV1 expressed as % predicted was the least dependent on initial FEV1 and reversibilities, expressed as % initial or as % possible(predicted minus initial FEV1)were correlated with initial FEV1.