BACKGROUND Recommended treatment for moderate to severe asthma is the combination of an inhaled corticosteroid and a long-acting beta(2)-agonist. The present study was designed to compare a new fixed combination of extrafine beclomethasone and formoterol, with the fixed combination fluticasone and salmeterol. METHODS This was a phase III, multinational, multicentre, double-blind, randomized, two-arm parallel groups, controlled study. After a 2-week run-in period, 228 patients with moderate to severe asthma were randomized to a 12-week treatment with either beclomethasone 100 microg plus formoterol 6 microg or fluticasone 125 microg plus salmeterol 25 microg, both delivered two inhalations b.i.d. via a pressurized metered dose inhaler. RESULTS The analysis of noninferiority on the primary outcome, morning peak expiratory flow in the last 2 weeks of treatment, showed no difference between groups (difference -3.32 l/min; 95% CI -17.92 to 11.28). A significant improvement from baseline in lung function, symptom score and rescue medication use was observed in both groups at all time points. Beclomethasone plus formoterol combination showed a significantly faster onset of bronchodilation when compared with fluticasone plus salmeterol with the difference maintained for up to 1 h postdosing. No differences were observed between treatments in the rate of asthma exacerbations, frequency of adverse events and overnight urinary cortisol/creatinine ratio. CONCLUSIONS The new combination of extrafine beclomethasone plus formoterol is not inferior to the marketed combination of fluticasone and salmeterol in terms of efficacy and tolerability, with the advantage of a faster onset of bronchodilation. ( ClinicalTrials.gov number, NCT00394368).