The pharmacokinetics of the glucocorticoid budesonide was studied in 6 children with asthma after i.v. injection of 0.5 mg and oral inhalation of 1 mg as an aerosol. Budesonide is a 1:1 mixture of the epimers 22 S and 22 R, which were assayed separately by HPLC combined with RIA. All pharmacokinetic parameters of the epimers differed except the half-life of about 1.5 h. It was significantly shorter than that reported in adults. Plasma clearance averaged 103 l · h−1 for epimer 22 R and 74 l · h−1 for epimer 22 S; calculated per kg body weight these values were about 50% higher than in adults. The difference was about 40% when calculated per m2 of body surface area. Since budesonide is a high-clearance drug, the data indicate higher liver blood flow · kg−1 body weight and m2 of body surface area in children. The systemic availability of the aerosol was approximately 30% of nominal dose, i.e. the same as in adults. The high clearance and short half-life of budesonide in children are advantageous in reducing the risk of possible systemic side-effects of prophylactic treatment of asthma in childhood.