Background: Natural exposure to pollen provokes an increase in airway responsiveness in nonasthmatic subjects with seasonal allergic rhinitis. This natural exposure may induce inflammatory cell recruitment and cytokine release, leading to lower airway inflammation. Objective: The aim of this study was to characterize lower airway inflammation in nonasthmatic pollen-sensitive subjects. Methods: We performed immunohistochemical tests on bronchial biopsy specimens from subjects with rhinitis who had no past or current history of asthma to evaluate cytokine expression and inflammatory cell numbers and activation both in and out of the pollen season. Results: The number of CD4⁺, CD8⁺, and CD45RO⁺ lymphocyte subpopulations were significantly higher during the pollen season compared with the out-of-season period (P < .04). Furthermore, EG1⁺ cells tended to increase after natural pollen exposure (P = .06). The number of IL-5⁺ cells increased significantly after natural exposure to pollen compared with out-of-season numbers (P < .01). This increase in IL-5 expression was correlated with the numbers of CD3⁺, CD4⁺, CD45RO⁺, and EG1⁺ cells. The numbers of tryptase-positive, IFN-γ⁺, and IL-4⁺ cells did not change after natural exposure. Conclusion: This study showed that natural pollen exposure was associated with an increase in lymphocyte numbers, eosinophil recruitment, and IL-5 expression in the bronchial mucosa of nonasthmatic subjects with allergic rhinitis. (J Allergy Clin Immunol 2000;106:904-10.)