This is a modified blind, randomized, multicenter, single dose two-way crossover study to assess the efficacy and safety of arformoterol 15μg BID versus arformoterol 30μg QD in subjects with COPD. Subject participation will last approximately three weeks and will include a screening visit, two 24-hour visits, and a follow up telephone call. 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.