This is an open label, randomized, multiple dose, 3-way crossover, multicenter, inpatient and outpatient study to compare the pharmacokinetic (PK) profile of arformoterol tartrate inhalation solution and Foradil® in male and female subjects with mild to moderate COPD. Up to 36 subjects (with a minimum 40% of each gender) were to be randomized to ensure that at minimum 24 subjects completed the study. The study included 3 dose periods and 3 washout periods. Subjects received 3 different treatments in random order for 13 consecutive days and a single dose on the morning of the 14th day. Subjects will be randomly assigned to 1 of the 6 possible treatment sequences. During each dose period, subjects received medication via nebulization or DPI twice daily for 13 consecutive days and a single dose on the morning of the 14th day. There was be a 10 day washout period between each treatment. Subject participation was be approximately 13 weeks and included a screening visit and 7 study visits. This study was previously posted by Sepracor Inc. In October 2009, Sepracor Inc. was acquired by Dainippon Sumitomo Pharma., and in October 2010, Sepracor Inc's name was changed to Sunovion Pharmaceuticals Inc.