Evaluate the additive role of zileuton 600mg qid to clinically stable asthmatics on Advair 250/50 bid. Since asthma is an endogenous inflammatory disease there usually is increased total exhaled, bronchial and alveolar nitric oxide which are markers of eosinophilic driven pathways of inflammation. The addition of zileuton which is a leukotriene synthesis inhibitor by itself or together with inhaled corticosteroids should reduce nitric oxide gas exchange.