This study looked at the effects of natural antigenic exposure on non-specific airway responsiveness (NSAR) in pollen-sensitized non-asthmatic subjects with seasonal rhinitis. Eight subjects had daily recordings of their respiratory symptoms and peak flow rates during and out of the pollen season. Airway response to methacholine was measured at 1-week to 2-week intervals. Pre-season spirometry and NSAR were normal in all subjects. Their PC20 methacholine ranged from 64 to greater than 256 mg/mL. During natural pollen exposure, all subjects had symptoms of rhinoconjunctivitis. The only chest symptom observed was coughing. No significant change in peak flow rates was observed throughout the study. A significant increase in bronchial responsiveness to methacholine occurred in five subjects although it did not reach the asthmatic range (less than 16 mg/mL). This change in NSAR was reproduced after antigen (tree pollen) challenge in the laboratory in one of the subjects. A significant increase in blood eosinophils was observed during seasonal pollen exposure. This study shows that following natural antigenic exposure, NSAR can increase in non-asthmatic subjects with allergic rhinitis, although it may not reach the "hyperresponsive range," and is associated with the development of a cough. These data suggest that natural exposure in non-asthmatic atopics may induce an inflammatory reaction in the airways to a degree that may increase NSAR.