The Improving Asthma Control Trial (IMPACT) was a double-blind, randomized, parallel group design clinical study to determine the best long-term strategy for treating adults with mild asthma who experienced symptoms more than occasionally. The study tested whether these patients should be taking anti-inflammatory medications on a daily basis and whether a newer class of medications provided the same benefit as older drugs. In the IMPACT study, 225 adults with mild asthma, who had more than occasional symptoms, were enrolled in six clinical research centers. Following an initial evaluation, patients were randomized to receive either a twice daily inhaled corticosteroid, a twice daily anti-leukotriene, or a placebo. All patients received treatment for symptoms if, and when, they occured. The primary outcome was AM PEF. Other outcomes included FEV1 before and after bronchodilator treatment, the frequency of exacerbations, the degree of asthma control, the number of symptom-free days, and the quality of life. Recruitment ended in 2003. Study results were published in the April 14, 2005 issue of the New England Journal of Medicine. In April 2001 NHLBI initiated an ancillary study to IMPACT entitled "Modification of Allergic Immunologic Response by Leukotriene Antagonists" under R01HL67684. The ancillary study has its own site in this database.