 Children between the ages of 6 and 17 years inclusive who have a history of asthma are eligible for enrollment if they present to the pediatric emergency department with a moderate to severe acute asthma exacerbation. All eligible children will be enrolled whenever there are study personnel available after obtaining informed written consent. Children less than 6 years of age will not be enrolled as levalbuterol has only been approved in children 6 years of age and greater. Children will also be excluded if their Forced Expiratory Volume in 1 sec FEV 1 is 70 predicted see below; they have a history of a chronic lung disease e.g. cystic fibrosis, noncorrected congenital heart disease, suspected intrathoracic foreign body, need immediate resuscitation or are pregnant. 