The purpose of the present study was to investigate: 1) whether tidal flow patterns can be used to discriminate between children with asthma and those without respiratory illness; and 2) whether reversibility to salbutamol in young children can be detected by tidal breathing analysis? Lung function was measured by tidal flow-volume loops (SensorMedics 2600) in 26 awake young children (13 males) with asthma (aged 7-85 months; mean age 33 months), and 26 (13 males) (aged 3-72 months; mean age 34 months) without respiratory illness, before and 15 min after inhalation of nebulized salbutamol, 0.05 mg.kg-1. The ratios of the time and volume until peak expiratory flow to the total expiratory time and volume, respectively, (TPEF/TE and VPEF/VE), and the ratio of tidal expiratory flow at 25% remaining expiration to peak expiratory flow, TEF25/PEF, were significantly lower in asthmatic children than in controls, and increased significantly after salbutamol inhalation in the former. Conversely, TPEF/TE and VPEF/VE, but not TEF25/PEF decreased significantly in the controls after salbutamol inhalation. Respiratory rate and expiratory volume.kg-1 body weight did not differ significantly between the two groups before and after salbutamol inhalation. We conclude that tidal breathing analysis can discriminate young children with asthma from children without respiratory illness, both regarding baseline lung function and reversibility to salbutamol.