 Spirometry will be performed at baseline and after each hour of bronchodilator treatment until the child is discharged home or is admitted to an in-patient unit. Patient disposition from the ED depends on their response to treatment. The ultimate decision to admit or discharge will be at the attendings discretion. However, if the child is able to perform good loops on spirometry then FEV1 may be used to guide the decision. An FEV 1 70 predicted will likely mean discharge to home with appropriate instructions. Children will be observed for 60 minutes after their last bronchodilator treatment to ensure that they maintain their response. Children will be admitted to the PICU if their FEV 1 50 or if they require inhaled bronchodilators more than hourly. If the childs FEV 1 is 50 but 70 or if they are still experiencing moderate symptoms they are likely to be admitted to the floor but further treatment in the ED may allow sufficient improvement for discharge. If after a further treatment period of one hour their FEV1 is 70 they will be discharged home. If it is 70 they will be admitted. Once disposition has been decided the study is concluded for that patient except for telephone follow-up if the child was discharged home. 