Allergic asthma and rhinitis are manifestations of the atopic syndrome and often coexist. It has been demonstrated that allergic rhinitis is a strong risk factor for the onset of asthma in adults. Genetic and environmental factors are recognized as contributing factors to the development of the allergic airway syndrome. Insight in the risk factors responsible for allergic airways disease and the interaction between the involved organs results in a better understanding and treatment of the syndrome. Several mechanisms have been proposed for the interaction between upper and lower airways in allergic rhinitis and asthma. It has been clearly shown in many studies that impaired nasal function affects the lower airways of patients with asthma. The evidence for aspiration of nasal contents or neural reflexes as an explanation for nasobronchial cross-talk is lacking. To date, most human and animal data point toward a systemic pathway linking the upper and lower airways, involving both bloodstream and bone marrow. Serum IL-5 and blood eosinophils are increased as well as adhesion molecule expression after local allergen challenge. Moreover, mucosal inflammation was not restricted to the challenged organ only, but extended throughout the whole airway in subjects with allergic rhinitis. Nasobronchial interaction in allergic airway disease has profound impact on daily clinic. Nasal therapy in allergic rhinitis patients with asthma has a beneficial effect on asthma symptoms, bronchial hyperresponsiveness, and airway inflammation. Furthermore, it reduces the risk of asthma exacerbations. It stresses the importance of an integrated therapeutic approach involving both ends of the respiratory tract.