Over the last 20 years, the prevalence of asthma has nearly doubled and now affects 8-10% of the population in the United States. Asthma also remains a major illness in terms of morbidity and suffering, and is the leading cause of hospitalizations in children under 15 years of age. Because asthma poses a lifelong burden to patients and society, efforts to increase the understanding of its pathogenesis are a key factor leading to its control and cure. Consequently, the National Heart, Lung, and Blood Institute (NHLBI) convened a Working Group of extramural experts, entitled "Future Research Directions in Asthma," on April 9-10, 2003, to identify research areas of greatest promise and opportunity in the field of asthma. The priority areas identified for research in asthma include: (1) innate immunity, adaptive immunity, and tolerance; (2) mechanisms and consequences of persistent asthma and asthma exacerbations; (3) airway remodeling: clinical consequences and reversibility (clinical relevance and resolution); (4) genetics/gene-environment interactions, pharmacogenetics; (5) intervention/prevention/therapeutics; and (6) vascular basis of asthma.