We evaluated the bronchodilatory and the bronchoprotective effect of the long-acting beta(2)-agonist formoterol administered as dry powder from a mechanically actuated dry-powder inhaler (DPI) using spacer in 12 asthmatic children 2 to 5 yr of age. Lung function was measured as the specific airway resistance (sRaw) in a whole body plethysmograph. Hyperventilation of cold, dry air was used as bronchial challenge, and the responsiveness was estimated as change in sRaw. The bronchoprotective effect of formoterol Turbohaler 9 microg was compared with salbutamol 200 microg and placebo at 15 min, 4 and 8 h postdose in a randomized, double-blind, placebo-controlled, crossover study. All treatments were administered from DPI (Turbohaler) actuated mechanically into a spacer. Formoterol and salbutamol caused similar and significant bronchodilation at the first measurement 3 min postdose. Formoterol offered a sustained and stable bronchodilation for at least 8 h. Salbutamol provided significant bronchodilation for less than 4 h. Formoterol caused significant bronchoprotection of 80% for at least 8 h compared with placebo, and from 4 h onward compared with salbutamol. Bronchoprotection from salbutamol lasted less than 4 h. In conclusion, formoterol administered as dry powder in a single dose provided rapid and sustained bronchodilation and clinically significant bronchoprotection for at least 8 h in 2- to 5-yr-old asthmatic children. Furthermore, this study suggests that mechanical actuation of DPI using a spacer is effective for aerosol treatment of young asthmatic children.