Asthma is a chronic inflammatory disease of the lower airways. The inflammatory process is associated with changes in airway hyperresponsiveness (irritability), and airflow limitations caused by bronchoconstriction, edema, and mucous plugging. Mast cells, basophils, eosinophils, activated T-lymphocytes, macrophages, neutrophils, and airway epithelial cells all play a role in this inflammatory process by releasing mediators directly responsible for local inflammation and by releasing mediators that encourage a further influx of inflammatory cells (Expert Panel Report 2, 1997). These cells and their products eventually produce a state of chronic allergic inflammation leading to increased vascular leakage, mucous secretion, smooth muscle hyperresponsiveness, and nerve activation. Clinically, this process is characterized by intermittent shortness of breath, wheezing, coughing, and chest tightness.