This study will use a randomized, double-blind, controlled trial design in order to assess the safety and efficacy of LEV compared to RAC when delivered continuously in a high-dose regimen for severe exacerbations of asthma. Children treated for asthma exacerbations in the CHOP emergency department (ED) will be eligible for study enrollment. Those that meet enrollment criteria will be randomized to receive either high dose RAC according to the standard asthma care protocol or equivalent dosing of LEV. Approximately 128 patients with 64 in each arm of the study will be enrolled. An interim safety analysis will be conducted after the first 40 patients are enrolled. This study should be completed in six to nine months. The primary outcome will be duration of continuous therapy. Secondary outcomes will include improvement of clinical asthma score and change in forced expiratory volume in one second (FEV1). In addition, (R)-albuterol and (S)-albuterol levels will be measured at study entry and at 6-hour intervals in the first 40 patients enrolled. These values will be used to determine prior RAC exposure and to determine serum levels of (R) and (S) albuterol during continuous therapy.