This study evaluated the effect of mometasone furoate (MF)/formoterol (F) versus its monocomponents, each administered via metered-dose inhaler, on asthma deteriorations and lung function. This 26-week, multicentre, double-blind, placebo-controlled study included subjects aged ≥12 yrs with not well-controlled asthma on low-dose inhaled corticosteroids. After a 2-3-week open-label run-in (MF 100 μg b.i.d.), 746 subjects were randomised to receive placebo, F 10 μg, MF 100 μg or MF/F 100/10 μg b.i.d. Co-primary end-points were time to first asthma deterioration (MF/F versus F to assess effect of MF) and change in forced expiratory volume in 1 s (FEV(1)) area under the curve of serial spirometry measurements over the 12-h period following the morning dose (AUC(0-12h)) (baseline to week 12; MF/F versus MF to assess effect of F). The therapeutic effect of MF in the combination was demonstrated by a reduction in asthma deterioration incidence with MF/F versus F and a delayed time to first asthma deterioration (p