OBJECTIVE:To assess the bronchodilator efficacy, safety and tolerability of indacaterol, a novel, once-daily inhaled beta(2)-agonist bronchodilator, in patients with chronic obstructive pulmonary disease (COPD). METHODS:This crossover, double-blind, double-dummy study was conducted to evaluate the 24-h bronchodilator effect of a range of single doses of indacaterol (150 microg, 300 microg and 600 microg), given in the morning via single-dose dry powder inhaler (SDDPI) in subjects with COPD, compared with placebo and with the daily therapeutic dose of formoterol (two 12 microg doses 12 h apart, via an SDDPI). Tolerability and safety were also assessed. RESULTS:Fifty-one subjects with moderate-to-severe COPD received each of the five treatments on separate study days in randomised sequence. The 24-h trough FEV(1) (primary endpoint; mean [95% CI]) was 1.46 (1.43, 1.49) L with indacaterol 600 microg (p < 0.001 vs. placebo, p < 0.01 vs. formoterol, p < 0.05 vs. indacaterol 150 microg), 1.45 (1.42, 1.48) L with indacaterol 300 microg (p < 0.001 vs. placebo, p < 0.05 vs. formoterol), 1.42 (1.39, 1.45) L with indacaterol 150 microg (p < 0.001 vs. placebo), 1.41 (1.38, 1.43) L with formoterol (p < 0.001 vs. placebo) and 1.28 (1.25, 1.31) L with placebo. All treatments were well tolerated and there was little effect on serum potassium, blood glucose or QTc interval. CONCLUSION:All doses of indacaterol were effective in providing 24-h bronchodilation and were well-tolerated in subjects with COPD. The bronchodilator efficacy of indacaterol (150, 300 and 600 microg) at 24 h post-dose was at least as efficacious as formoterol 12 microg twice daily.