Airway hyperreactivity is a consistent finding in most children with asthma and is responsible for many of the clinical manifestations of asthma. Bronchial hyperreactivity (BHR) in children has been elicited by bronchial challenge with methacholine and histamine, by cold air (isocapnic hyperventilation), and by exercise. Pharmacologic agents employed in therapy of childhood asthma that may modulate both the late asthmatic reaction and bronchial hyperreactivity include cromolyn sodium, glucocorticoids, and possibly ketotifen. β-Adrenergic agonists, though effective in blocking the early asthmatic response, had no effect on the late response and did not alter bronchial hyperreactivity. Theophylline in both children and adults, and enprophylline (not yet studied in children) may modify both the early and late response but do not appear to have an effect on bronchial hyperreactivity. New drugs which may have potential value in reducing bronchial hyperreactivity include calcium channel blockers and platelet-ac...