3. Study Design: Phase 2 clinical pharmacokinetic/pharmacodynamic trial in pediatric patients aged 2-18 years old who are receiving intravenous terbutaline for a severe asthma attack. Three groups of 12 children will be examined based on age for a total N of 36. The first group will be 2-6 years, the second group will be 6-12 years old and the third will be adolescents 12-18 years old. Treatment efficacy will be gauged by comparing scores of the modified pulmonary index (MPIS) as well as utilization of the rescue medication protocol (see below). Pharmacokinetics and pharmacodynamics will be determined by serum samples collected in 1-2 ml aliquots prior to infusion and at 20 minutes, 2, 4, 6, 8, 10, and 12 hours post infusion, or until clinical improvement necessitates discontinuation of the infusion if less than 12 hours.