The efficacy of the modes of inhalation of 2 inhaled steroids (IS) were compared: beclomethasone dipropionate (BDP) delivered by pressurised metered dose inhaler (p MDI) and budesonide delivered by the inspiratory driven powder inhaler Turbuhaler®.146 asthmatic patients (mean age ± SD: 49 ± 13 years) treated for at least 6 months with constant doses of BDP (1000 to 2000μg per day) entered into an open, parallel group trial. After a 4-week run-in period, they were randomised to receive either BDP or budesonide at supposedly equivalent doses (BDP 1 puff 250μg ≡ budesonide 1 dose 200μg) for 12 weeks. Every 4 weeks the daily dose of IS was adjusted for control of disease as assessed by a 4-graded asthma score.Both treatment groups were comparable: puffs/doses (mean ± SD) of IS per day at randomisation were 5.6 ± 1.5 for the budesonide group versus 5.8 ± 1.4 for the BDP group (p = NS). 18 patients (10 in the budesonide group, 8 in the BDP group) did not complete the trial. At the end of the study, symptoms of asthma, morning and evening peak expiratory flow, puffs of &bgr;2-agonists per 24 hours, and short courses of oral steroids were comparable, but puffs/doses of IS per day (primary efficacy variable) were significantly lower in the budesonide than in the BDP group (4.5 ± 2.1vs5.4 ± 2.0; p = 0.009).The results of this trial show that budesonide administered via Turbuhaler®is more effective per μg than BDP delivered by p MDI.