There are numerous parameters for the detection of obstructive airway disease in Maximal Expiratory Flow Volume Loop(Curve). Slope-Ratio(SR) is another new parameter which considered to be useful for the detection of early small airway dysfunction using both MEF 50 and MEF 75• SR was measured in 3 groups of subjects(50 person in each group) and obtained the following results. 1) SR of first group, who have normal limit values of FVC, FEV1.0, MEF 50, MEF75, was 0.86土 0.24. 2) SR of second group, who have less then 70% predicted MEF 75 but all normal FVC, FEV1.0, MEF 50, showed 1.30土0.15 3) SR of third group, who have less than 70% predicted MEF 50, FEV1.0, was 1. 38 土 0.19. 4) Arbitrary value of SR 1.0 appeared to be the marginal value of Small Airway Dysfunction(SAD) in functional aspect. 5) Further SR analysis among the evident obstructive airway disease patients will be needed for the clinically useful parameter.