Background: Inhaled corticosteroids have a greater antiinflammatory potency and fewer systemic effects than intravenous, intramuscular, or oral corticosteroids. However, their role in acute asthma has not been established. We prospectively investigated the efficacy and safety of inhaled corticosteroids in controlling moderately severe acute asthma attacks in children who were treated in the emergency department. Methods: Children who were treated in the emergency department with moderately severe asthma attacks after receiving treatment with inhaled terbutaline were allocated by double-blind design to receive 1 dose of either 1600 μg budesonide turbohaler or 2 mg/kg prednisolone. The pulmonary index score and peak expiratory flow rate were measured hourly for the first 4 hours. After discharge the children were treated with the same initial doses given 4 times daily, followed by a 25% reduction in dose every second day for 1 week. Parents recorded asthma symptoms and use of β-2 agonists on a daily diary card. Serum cortisol concentration was measured at the end of weeks 1 and 3. Results: Twenty-two children (11 in each group) with similar baseline parameters completed the study. There was a similar improvement in pulmonary index score and peak expiratory flow rate in the 2 groups. Children treated with budesonide showed an earlier clinical response than those given prednisolone, who also showed a decrease in serum cortisol concentration. Conclusion: In children with moderately severe asthma attacks who were treated in the emergency department, a short-term dose schedule of inhaled budesonide turbohaler, starting with a high dose and followed by a decrease over 1 week, is at least as effective as oral prednisolone, without suppressing serum cortisol concentration. (J Allergy Clin Immunol 1998;102:605-9.)