||The aims of this study were to investigate lung function in 2-5-yr-old stable asthmatic children consecutively referred from general practitioners and to analyse the outcome on the basis of their requirement for antiasthmatic treatment and symptoms after 1.6-4.5 yrs. Lung function was measured in 110 children with a mean+/-SD age of 3.8+/-1.0 yrs using the interruptor technique (resistance assessed using the interruptor technique (Rint)), whole body plethysmography (specific airway resistance (sRaw) and respiratory resistance (Rrs,5)and reactance at 5 Hz (Xrs,5) using the impulse oscillation technique. Rint, sRaw, Xrs,5 and Rrs,5 were suggestive of impaired lung function in 44%, 14%, 11% and 7.5% of the children, respectively, with a predominance of children aged 2-3 yrs. Sixty-five per cent were treated with inhaled steroids, and 35% were treated only with beta2-agonists as needed; lung function was not significantly different between these two groups. Outcome after 2.9+/-0.7 yrs was not significantly different between children with Rint measurements above and those children with Rint measurements within the reference range at enrolment. Of these children, 58 and 59% were currently on antiasthmatic treatment, and 40% and 49% had current symptoms, respectively. Impairment of lung function may be a common finding in stable young asthmatic children, but apparently this is not a risk factor for persistence of asthmatic symptoms.