BACKGROUND Indacaterol is a novel, inhaled once-daily ultra-long-acting β(2)-agonist for the treatment of COPD. METHODS This 12-week randomised, parallel-group study compared the efficacy of indacaterol 150 μg once-daily to salmeterol 50 μg twice-daily in patients with moderate-to-severe COPD. Assessments included FEV(1) standardised area under curve (AUC) from 5 min to 11 h 45 min at Week 12 (primary endpoint), 24-h trough FEV(1) (mean of 23 h 10 min and 23 h 45 min post-dose) at Week 12 (key secondary endpoint), FEV(1) and FVC measured over 24-h, transition dyspnoea index (TDI) and rescue medication use. RESULTS Of 1123 patients randomised 92.1% completed. Mean ± SD age was 62.8±8.78 years, post-bronchodilator FEV(1) 51.8±12.32% predicted, FEV(1)/FVC 50.6±9.54%. At Week 12, FEV(1) AUC(5 min-11 h 45 min) for indacaterol was statistically superior (p<0.001) to salmeterol (adjusted mean difference [95% CI] 57 [35, 79] mL), as was 24-h trough FEV(1) (60 [37, 83] mL, p<0.001). Indacaterol also showed statistical superiority over salmeterol in terms of FEV(1) and FVC measured over 24-h at Week 12. For TDI at Week 12, the mean total score was statistically superior for indacaterol versus salmeterol (difference 0.63 [0.30, 0.97], p<0.001), as was the percentage of patients with a clinically relevant (i.e., ≥1 point) change from baseline (69.4% vs 62.7%, p<0.05). For rescue medication, patients on indacaterol used fewer puffs/day (difference -0.18 [-0.36, 0.00] puffs/day, p<0.05) and had a greater percentage of days with no rescue use (difference 4.4 [0.6, 8.2], p<0.05). CONCLUSIONS Once-daily indacaterol provided statistically superior bronchodilation with an improvement in breathlessness and rescue use compared with twice-daily salmeterol. ClinicalTrials.gov NCT00821093.