Severe asthmatics remain poorly controlled despite high doses of standard asthma therapy or even daily doses of systemic corticosteroids or their equivalent. They account for a large proportion of the morbidity and mortality associated with asthma. Features that seem to characterize many patients with this disorder include persistent inflammation, symptoms, and airway hyperresponsiveness in the face of corticosteroid therapy. Mast cells are powerful, long-lived tissue dwelling effector cells that are resistant to corticosteroid effects and have been implicated in the pathobiology of asthma. Mast cells in the airway smooth muscle have been found to be the major distinguishing difference between asthmatic and non-asthmatic eosinophil airway disease; and putative circulating mast cell progenitors are increased 5 fold in asthma. Stem cell factor (SCF) is critical to mast cell homeostasis and upregulation and has pleiotropic effects on mast cells and eosinophils . SCF levels are elevated in relation to asthma severity and SCF antibodies block hyperresponsiveness and inflammation and remodeling in murine asthma models. Imatinib, a specific tyrosine kinase inhibitor, inhibits cKit (Kit), the receptor for SCF on mast cells. Imatinib at doses equivalent to, or below, doses safely used in humans, also mimics or exceeds anti-SCF effects in the murine asthma model. Therefore we would like to know Does imatinib, an inhibitor of Kit, ameliorate severe asthma, in association with effects on lung mast cell phenotype and/or function?