Aims: We have compared the ability of plethysmography (sGaw), impulse oscillometry (IOS) and spirometry (FEV1, MMEF) to detect bronchodilation in response to an anticholinergic. Methods: IOS (R5, R20, X5, RF), sGaw and spirometry were measured in 12 healthy subjects and 12 asthmatics. Variability was assessed by performing two measurements, 30 min apart and the effect of increasing the number of readings for each sGaw measurement was also studied. Ipratropium bromide (IB) 10, 20, 100 and 200 μg was administered and the sensitivity of the methods compared by determining the lowest dose that caused changes greater than variability. Results: In healthy subjects significant changes (P ≤ 0.05) occurred at 10 μg for FEV1 (mean [95% CI]; 1.3% [0.3-2.3]), R5 (mean [95% CI]; -7.9%, [-13.2-2.6]) and R20 (mean [95% CI], -6.4%, [-11.4-1.4]). No significant change was detected when the mean of 3 sGaw readings was used, but with 10 readings significant change was observed at 20 μg; (mean increase [95% CI] 15.2% [8.3-22.1]). In asthmatics significant changes (P ≤ 0.05) occurred with IB 10 μg for sGaw (mean [95% CI] 25.6% [11.1-40.1]), R5 (mean [95% CI] -11.3%, [-15.5-7.2]), RF (mean [95% CI] 11.7% [6.1-16.3]), FEV1 (mean [95% CI] 5.1% [2.6-7.7]) and MMEF (mean [95% CI] 12.3% [2.3-22.2]). Conclusion: IOS and spirometry are more sensitive than sGaw in healthy subjects, but the sensitivity of sGaw improved when the number of readings was increased. The most sensitive method for assessing bronchodilation in asthmatics was sGaw.