Pharmacokinetic studies can be used to measure lung dose of inhaled drugs. Aim: To compare the lung deposition of budesonide inhaled from Turbuhaler and fluticasone inhaled from Diskus and to assess if the study design used for pharmacokinetic studies can be simplified. Method: Plasma levels of Budesonide and Fluticasone were measured for 21 hours on 5 separate days in 15 patients aged 8 to 14 years: 1) Intravenous infusion of 200 [mu]g Budesonide, 2) Intravenous infusion of 200 [mu]g Fluticasone 3) Inhalation of 800 µg Budesonide via Turbuhaler 4) Inhalation of 750[mu]g Fluticasone via Diskus 5) Inhalation of Budesonide and Fluticasone on the same day. Charcoal was ingested to eliminate drug uptake from the gastrointestinal tract. Results: Mean lung deposition of drug after Turbuhaler and Diskus inhalation was 30,8% (Budesonide) and 8.0% (Fluticasone) when the drugs were administered on separate days and 29.5% (Budesonide) and 7.6% (Fluticasone) when they were inhaled on the same day. Conclusion: Lung deposition is four times higher in children after inhalation from Turbuhaler than after inhalation from Diskus. Pharmacokinetic studies with budesonide and fluticasone can be simplified since the two treatments can be administered on the same day.