Urbankowski T, et al. - This study, including adult individuals referred for methacholine challenge testing (MCT) due to asthma-like symptoms and with normal baseline spirometry, was conducted to determine the diagnostic worth of airway resistance measurement by forced oscillation technique (FOT), body plethysmography, and interrupter technique vs the conventionally accepted standard FEV ₁ measurement in assessing the responsiveness to methacholine during MCT. Experts added airway resistance evaluation to FEV ₁ measurement at each step of MCT, and thereby altered routine MCT protocol. A significantly greater % alteration in median FOT resistance at 10 Hz, plethysmographic resistance, and mean ± SD conductance; as well as a significantly greater alteration in mean ± SD FOT reactance at 10 Hz and at 15 Hz was detected in participants with airway hyper-responsiveness vs those with normal airway responsiveness. In this study, the likely utility of measurements of airway resistance was indicated as an alternative tool to spirometry in airway challenge. In FEV ₁ non-responders with methacholine-induced asthma-like symptoms, airway resistance measurement can detect significant alterations in airway mechanics during MCT.