Allergic rhinitis and bronchial asthma frequently coexist in the same patients. Many patients with rhinitis alone demonstrate nonspecific bronchial hyperresponsiveness, and prospective studies suggest that nasal allergy may be a predisposing risk factor for developing asthma. A growing body of literature has documented that the treatment of patients with allergic rhinitis may result in improvement of asthma symptoms, airway caliber, and bronchial hyperresponsiveness to methacholine and exercise. Finally, mechanistic studies of airway physiology have demonstrated that nasal disease may influence pulmonary function via both direct and indirect mechanisms. Nasal disease should be considered as a possible concomitant illness in all patients with asthma and treated appropriately when identified.