Asthma is a common respiratory illness characterized by airway hyperresponsiveness and inflammation. It affects over 300 million people globally (1), including 22 million adults in the United States alone. Although asthma mortality in the United States has declined, the morbidity and costs remain substantial. In certain groups of Americans, such as persons of lower socioeconomic status and minority ethnicity, asthma morbidity and mortality are disproportionately high. Such trends are surprising, given the improvement in air quality in the United States and the availability of effective therapies.