Background Airway hyperresponsiveness (AHR) is one of the most important characteristics of asthma. This study investigated the parameters, by which assess the airway responsiveness under tidal ventilation.Methods Female BALB/c mice were sensitized and challenged with ovalbumin (OVA) (group A), and part of them were treated with budesonide aerosol (group B). All the mice were anaesthetized and mechanically ventilated. The values of tidal volume (Vt), airway pressure (PA), airway flow (F), expiratory lung resistance (RL) and dynamic compliance of the thorax and lung (CT-L) were recorded by the AniRes2003 animal lung function system. In addition, the expiratory volume in the first 0.1 second after the start of expiration (EV0.1) was obtained according to the flow-volume (F-V) curve. The maximal or minimal values of EV0.1, RL and CT-L were documented after each dose of methacholine (MCH) and compared with values from negative control group (group C).Results (1) When the dose of MCH reached 100 ng/g or 200 ng/g, the decrease of Vt in group A was much more significant than group C (P=0.001,