Pharmacokinetic studies can be used to measure lung dose of inhaled drugs. The aim of this study was to compare the lung deposition of budesonide (BUD) inhaled from Turbuhaler (AstraZeneca, Lund, Sweden) and fluticasone propionate (FP) inhaled from Diskus (GlaxoSmithKline, London, UK) and to assess if the study design used for pharmacokinetic studies can be simplified. Plasma levels of BUD and FP were measured for 21 hours on five separate days in 15 patients aged 8 to 14 years: (1) Intravenous infusion of 200 microg BUD, (2) intravenous infusion of 200 microg fluticasone dipropionate, (3) inhalation of 800 microg BUD via Turbuhaler, (4) inhalation of 750 microg FP via Diskus, and (5) inhalation of BUD and FP on the same day. Charcoal was ingested to eliminate drug uptake from the gastrointestinal tract. The mean lung deposition of drug after Turbuhaler and Diskus inhalation was 30.8 and 8.0% when BUD and fluticasone were administered on separate days and 29.5% (BUD) and 7.6% (fluticasone) when the two drugs were inhaled on the same day. Lung deposition is four times higher in children after inhalation from Turbuhaler than after inhalation from Diskus. Pharmacokinetic studies with BUD and FP can be simplified because the two treatments can be administered on the same day.