Asthma is an increasingly serious cause of morbidity and mortality in the United States. There are approximately 12 million asthmatics, and the disease affects both sexes and impacts all racial and ethnic groups. It is now recognized that asthma is a complex disease of varied etiology, which is triggered by a number of factors (e.g., allergens, drugs, chemicals, exercise, cold air, infections, and emotions), making asthma therapy difficult and sometimes complicated. Multiple drugs, including medications to treat and control symptoms (bronchodilator agents such as beta-adrenergic agonists, theophylline, and anticholinergics) and medications thought to control underlying airway inflammation (e.g., inhaled and systemic corticosteroids, cromolyn sodium, and nedocromil), are often required.