Ninety-eight children aged 1-15 years entered a randomized double-blind study investigating an appropriate dose of oral prednisolone in children admitted to hospital with an acute exacerbation of asthma. None of the children had recently been treated with oral prednisolone. Following admission, the children were randomized to receive prednisolone 0.5 mg kg-1, 1.0 mg kg-1 or 2.0 mg kg-1 in a single daily dose in addition to nebulized bronchodilators. Clinical asthma scores, oxygen saturations, pulse rate, duration of admission and number of nebulizers given were compared in the three treatment groups. Thirty-five children received 0.5 mg kg-1, 33 received 1.0 mg kg-1 and 30 received 2.0 mg kg-1. There were no significant differences in the pattern of recovery between the three treatment groups. There were no advantages in using higher doses of prednisolone. We recommend 0.5 mg kg-1 day-1 of prednisolone as an appropriate dose for treating an acute exacerbation of asthma.