Asthma manifests itself in a two-phase reaction. An early phase, causing bronchial muscle contraction, occurs within minutes after an antigenic stimulus. Within 6 to 18 hours, a late asthmatic response begins. This response is associated with cellular infiltration of the bronchial submucosa by eosinophils, neutrophils, and lymphocytes. The late asthmatic response is most effectively reversed by the use of corticosteroids. Predicting patient outcome solely on the basis of either physical findings, or pulmonary function tests, or historical events is frequently inadequate. Historical events, clinical assessments, and laboratory and pulmonary function measurements are best used in a complementary and integrated fashion to determine appropriate disposition of the acutely asthmatic patient.