The interrupter technique, forced oscillation and plethysmography have been increasingly used to monitor early childhood respiratory diseases over the past 30 years. The techniques are based on different principles but generally yield concordant information. Data from all three techniques indicate significant airway response to bronchodilators in healthy and asthmatic preschool children. The interrupter technique is useful but yields little more than a single value of respiratory resistance. Forced oscillation and plethysmography may provide additional information relevant to the mechanisms of airway obstruction, provided the methodological artefacts are accounted for and corrected.