A double-blind, randomized, placebo- and active-controlled, multicenter, parallel-group trial of levalbuterol in subjects 12 years of age and older with asthma. Study participation will include one 1-week single-blind placebo run-in and an 8-week, randomized,double-blind, active-treatment period with four treatment groups. 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.