Impulse oscillometry (IOS) is a computer-supported method for the measurement of complex mechanical airway characteristics. The aim of this study was to evaluate the applicability of IOS in the diagnosis of obstructive airway diseases in comparison to the standard methods of spirometry, pneumotachymetry, and bodyplethysmography. 244 patients (age 61.5 +/- 13.6 years; 61 % men) with bronchial asthma (n = 65) and chronic obstructive pulmonary disease (COPD) (n = 179) were retrospectively analysed. By means of body plethysmography (Srtot < 120%pred) an obstruction was diagnosed in 94%, by pneumotachymetry (FEV1 < 80%pred) in 78 %, and by IOS depending on the parameter chosen in 87-94% of patients. Mild and medium obstructions could be identified by means of all IOS parameters except for R20: severe obstructions, however, were better detected by means of the frequency-dependent resistance FDR and reactance at 5 Hz, X5. The parameters R5, X5, and Zrs, however, showed a tendency to underestimate the degree of obstruction. Bronchial obstruction can reliably be diagnosed by IOS when, in cases of severe obstruction, more complex parameters like FDR and X5 are included. The parameters of the standard methods (body plethysmography and pneumotachymetry) show relatively low correlations due to the different measurement methods not only in comparison to IOS but also to one another. In summary, IOS is a convenient method for patients with a low dependency on cooperation for the evaluation of obstructive airway diseases complementary to the established standard methods and, in addition, is useful as a sensitive screening tool for the early detection of bronchial obstruction.