The role of inhaled corticosteroids in asthma exacerbation is debated. We compared high doses of nebulized budesonide versus high doses of nebulized flunisolide, in association with a short-acting beta-2-agonist, in the treatment of moderate asthma exacerbation in preschool children. In this randomized, parallel group, simple blind study, 46 children aged between 3 and 5 years affected by an acute moderate asthma attack were treated with nebulized flunisolide (Group 1) 40 microg/kg twice daily for 7 days and then 20 microg/kg twice daily for 14 days, or with nebulized budesonide (Group 2) 0.5 mg twice daily for 7 days then 0.25 mg twice daily for 15 days. Inhaled salbutamol (MDI+ spacer - 200 microg 4 times daily) was administered during the first 3 days of the study and then as needed. At T0, T7 and T21 days, airway resistances were evaluated with the forced oscillation technique before and after inhalation of inhaled salbutamol (200 mcg). Parents recorded symptoms and drug use on a diary card. Forty children completed the study. Airway resistances were significantly reduced at T7 (p< 0.01 flunisolide; p< 0.05 budesonide) and T21 (p< 0.05 flunisolide; p< 0.05 budesonide) versus T0 in both groups, although at T7 the reduction occurred faster in group 1 than in group 2 (p<0.01). During the first 7 days of treatment, symptom scores decreased in both groups; however, the decrease was greater in group 1 (p< 0.05). High doses of inhaled flunisolide and budesonide are both effective in the management of moderate asthma exacerbations in pre-school-age children, but the flunisolide therapeutic effect was faster than budesonide.