 The aim of this study was to investigate the effectiveness of montelukast in wheezy very young children with persistent respiratory symptoms. This study was a prospective, double-blind, placebo-controlled study of 6 to 24 months old children, who had at least one physician-diagnosed wheezing episode and persistent asthmatic symptoms. Patients were randomised to placebo or montelukast 4 mg day for 8 weeks period. The clinical response to treatment was determined, the functional residual capacity FRC and specific air-way conductance sGaw was measured using an infant whole-body pletys-mograph, the maximal flow at functional residual capacity V maxFRC was re-corded using the squeeze technique and airway responsiveness was evaluated by performing a dosimetric methacholine challenge test. 