BACKGROUND Impulse oscillometry (IOS) is an effort-independent and patient-friendly pulmonary function technique, but limited data are available that correlate the bronchodilator response using spirometry and IOS in adult asthmatic and healthy subjects. OBJECTIVE To compare spirometry and IOS in ongoing bronchodilator response. METHODS The study was a prospective evaluation of patients with asthma and healthy subjects attending screening at a research unit in a university teaching hospital. Reversibility testing was carried out using standardized American Thoracic Society/European Respiratory Society (ATS/ERS) criteria after administering 400 μg salbutamol by AccuhalerTM. Impulse oscillometry measurements (resistance at 5 Hz [R5], resistance at 20 Hz [R20], reactance at 5 Hz [X5]) and spirometry (forced expiratory volume in 1 second [FEV(1)], forced vital capacity [FVC], forced expiratory flow from 25% to 75% of vital capacity [FEF(25-75)]) were recorded pre and postbronchodilator. RESULTS Ninety-five asthmatic and 61 healthy subjects underwent screening. Mean percent (standard error of the mean [SEM]) baseline prebronchodilator FEV(1) was 83.99 (2.23) for patients with asthma, and 99.25 (1.72) for healthy subjects. Baseline percent predicted IOS indices in the group with asthma were 162.22 (7.5) for R5; 154.73 (4.71) for R20; and 441.72 (173.86) for X5. In healthy volunteers, corresponding values were 111.01 (3.96), 127.75 (4.12), and -229.80 (125.75). R5 was the only IOS measure that showed correlation with spirometry (FEV(1)) in both groups. The mean percent (SEM) predicted postbronchodilator change in FEV(1) and R5 in patients with asthma was 6.35 (0.65) and -33.78 (4.43); correspondingly in healthy subjects it was 2.24 (0.32) and -14.91 (2.48). A negative correlation was demonstrated (r = -0.40, P < .001 between the 2 indices in patients with asthma. Linear regression modeling demonstrated that 1 unit change in %FEV(1) corresponds to a 2.5% change in %R5. CONCLUSIONS Low-frequency IOS as R5 and spirometry as FEV(1) correlate in patients with asthma and healthy subjects, with changes that can be predicted by linear regression.