Allergic rhinitis and asthma are two manifestations of the atopic syndrome. Allergic rhinitis often coexists with, and may even precede, allergic asthma. Both diseases are characterized by a similar inflammatory process in which mast cells and eosinophils are major effector cells. To date, however, interaction between the upper and lower airways' inflammatory processes has not been demonstrated. Allergen provocation studies provide a good model to analyse the aspects of naso-bronchial cross-talk. We performed segmental bronchial provocation (SBP) and nasal provocation (NP) in seasonal allergic rhinitis patients without asthma. In allergic rhinitis patients, SBP as well as NP induced allergic inflammation in both nasal and bronchial mucosa. Furthermore, allergen provocation resulted in an increase in circulating inflammatory cells and mediators. Although the clinical response was more severe after SBP, allergic rhinitis patients developed pulmonary symptoms and decreased airway function after NP as well. These studies demonstrate that allergic rhinitis is not a local disease, but that the entire respiratory tract is involved even in the absence of clinical asthma. The systemic pathway, involving bloodstream and bone marrow, contributes to the cross-talk between upper and lower airways.