Nitric oxide is a naturally occurring gas that plays a role in many body functions. Levels of eNO increase with airway inflammation, a symptom of asthma. Researchers have proposed using eNO as a noninvasive measure to guide physicians in the treatment and medical management of asthma in children. However, more information about eNO is needed before this can happen. This study will perform a secondary analysis of the results from its parent study, the CAP study, which evaluated the effectiveness of preventing asthma in children who had been exposed to environmental tobacco smoke.