 The study is designed to obtain safety and efficacy data on three dose levels of indacaterol when delivered via an SDDPI in patients with persistent asthma. All patients will receive 1 day of treatment with each of the following: indacaterol 150 μg, indacaterol 300 μg, indacaterol 600 μg, placebo, and formoterol. Each treatment day will be followed by a washout-period of 1 week 