Nocturnal asthma can be diagnosed by asking patients whether they awaken at night with asthmatic symptoms and feel the need to use an aerosol bronchodilator. The primary objective in treating nocturnal asthma is to help patients sleep through the night. The bronchoconstriction that underlies nocturnal asthmatic symptoms is a reflection of bronchial hyperresponsiveness, and this hyperresponsiveness is greatly increased by airway inflammation. In patients with allergic asthma, airway inflammation can be reduced by reducing exposure to allergens and, in some cases, by immunotherapy. Nocturnal bronchoconstriction is best controlled by scheduling sustained-release bronchodilators, particularly theophylline, to provide the maximal theophylline blood concentration at the time of maximal obstruction, usually between 4:00 and 6:00 A.M.