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).