A significant unmet medical need exists in patients with uncontrolled asthma. The purpose of this study was to evaluate the efficacy and safety of mometasone furoate/formoterol (MF/F) 400/10 microg versus MF 400 microg administered twice-daily (b.i.d.) via metered-dose inhaler in patients with asthma uncontrolled on high-dose inhaled corticosteroids (ICS). In a 12-week, randomized, multicenter, double-blind, parallel-group study, patients (>or=12 years of age) were randomized to MF/F 200/10 microg, MF/F 400/10 microg, or MF 400 microg, b.i.d. after a 2- to 3-week open-label run in with MF 400 microg b.i.d. The primary end point was mean change in area under the curve from 0 to 12 hours in forced expiratory volume in 1 second (FEV(1) AUC(0-12h)) from baseline to week 12 for MF/F 400/10 microg versus MF 400 microg. Effects of MF/F on asthma control and symptoms were evaluated and adverse events recorded. Seven hundred twenty-eight patients were randomized. Significant improvement from baseline to week 12 occurred for mean change in FEV(1) AUC(0-12h) with MF/F 400/10 microg (4.19 L x hour) versus MF 400 microg (2.04 L x hour; p <0.001). Both MF/F doses resulted in rapid (5 minutes) and sustained improvement in lung function throughout 12 weeks. Both MF/F doses were superior to MF in improving asthma control and reducing nocturnal awakenings due to asthma requiring short-acting beta(2)-agonist use. All treatments were well tolerated. Asthma patients who were poorly controlled on high-dose ICS experienced significant improvement in asthma control, lung function, and symptoms when treated with MF/F compared with MF.