The purpose of this study is to evaluate the Therapeutic Equivalence of Fluticasone Propionate 100mcg and Salmeterol 50mcg Inhalation Powder compared to the already approved marketed version of ADVAIR DISKUS 100/50 in the treatment of subjects with asthma. Both will be compared to a placebo inhalation powder which is not expected to have effect on your asthma symptoms. You will administer one inhalation of the investigational inhaler or placebo inhaler twice daily (approximately 12 hours apart) for 28 days. There's up to 5 visits and one visit requires you to spend 13 hours at our office. Total payment for the study will be $500. If you don't complete the study, you'll be compensated for the visits you complete.