The manifestation of rhinitic symptoms in 9 patients with grass pollen-induced rhinitis was studied during long term allergen exposure at physiological concentrations in the ‘Vienna Challenge Chamber’. Patients were pretreated with a single dose of azelastine (either 2.2mg orally or 0.28mg intranasally) or placebo. Nasal resistance was estimated by active anterior rhinomanometry every 15 minutes. Analysis of changes in nasal airways resistance demonstrated significant protection against allergen-induced nasal obstruction (p < 0.01) for azelastine administered by either route. The onset of action of treatment in relation to nasal obstruction was significantly more rapid for the nasal spray (135 minutes) than for the tablet (205 minutes) [p < 0.01] formulation. Similarly, the onset of effect derived from subjective assessment of symptom severity was markedly more rapid (60 minutes) after intranasal azelastine than after administration of the oral form (120 minutes). Tolerability of azelastine was good, with no side effects reported with either oral or intranasal therapy.