Knowledge of short- and longer-term repeatability of lung function in health and disease is essential to determine bronchodilator reversibility thresholds and to recognise if changes in lung function represent disease progression, therapeutic intervention or normal variability. Multiple-breath washout indices (lung clearance index, conductive ventilation inhomogeneity (Scond)) and specific airway resistance (sRaw) were measured in healthy children and stable wheezers. Measurements were performed at baseline and after 20 min without intervention to assess repeatability and determine bronchodilator reversibility thresholds. Bronchodilator reversibility was assessed by repeating baseline measurements 20 min after inhaled salbutamol. 28 healthy controls, mean±sd age 6.1±0.7 years and 62 wheezers 5.4±0.6 years were tested. Baseline variability in multiple-breath washout indices and sRaw was not significantly different between wheezers and healthy controls. Significant bronchodilator reversibility was only observed in wheezers for Scond (16%), but in both wheezers (37%) and healthy controls (20%) for sRaw. Some wheezers and healthy controls demonstrated increases in multiple-breath washout indices post-bronchodilator. Lung clearance index and sRaw demonstrate low baseline variability in healthy and diseased subjects. Neither multiple-breath washout indices nor sRaw are ideal for assessing bronchodilator reversibility in young children with stable wheeze. These findings will help to interpret the effect of therapeutic interventions in children with respiratory diseases.