Allergic rhinitis is a common chronic condition that is characterized by inflammation of the nasal mucosa. Although allergic rhinitis is a condition with upper respiratory symptoms, there is a growing body of evidence to suggest that allergic rhinitis may be linked to the development of systemic allergic manifestations that include allergic asthma. The evidence reveals that individuals with allergic rhinitis are sensitized to the eliciting allergens and exhibit cutaneous and respiratory hypersensitivity responses on exposure to the allergen. On exposure to a nasal allergen, circulating immunoglobulin E levels increased and remained elevated 2 weeks after the initial provocation. Patients with allergic rhinitis exhibit peripheral eosinophilia and basophilia, the magnitude of which correlates with the severity of symptoms. Additionally, there are several links between allergic rhinitis and asthma. First, 85% to 95% of patients with allergic asthma report rhinitis symptoms, and the severity of the 2 conditions increases in parallel on exposure to an allergen. Second, nasal administration of allergens can provoke impaired lower airway airflow in 25% to 30% of individuals and cause airway eosinophilia, as evidenced by increased numbers of eosinophils in sputum and mucosal biopsy specimens. Third, the treatment of seasonal allergic rhinitis with both systemic (eg, antihistamines) and local agents (eg, glucocorticosteroid analogues) can alleviate the symptoms of asthma. In summary, evidence that associates allergic rhinitis with systemic immunologic and inflammatory processes is growing, thereby warranting further in-depth investigation. (J Allergy Clin Immunol 2000;106:S247-50.)