Background: The relationship between airway inflammation and asthma severity in corticosteroid-treated asthma is unclear. Objectives: Our purpose was to characterize the inflammatory cell profile of the airway lumen and epithelium in corticosteroid-treated asthma and to relate these findings to clinical and physiologic markers of asthma severity. Methods: Adults (n = 20) with asthma received standardized high-dose inhaled corticosteroid therapy with beclomethasone 2000 μg per day for 8 weeks. Airway responsiveness to methacholine and hypertonic (4.5%) saline solution was then assessed, followed by sputum induction and, 1 week later, bronchoscopy with bronchoalveolar lavage and bronchial brush biopsy to assess inflammatory cells. Results: Clinical asthma severity was associated with airway hyperresponsiveness. Metachromatic cells were the main granulocyte present in bronchial brush biopsy specimens and correlated with airway responsiveness to saline solution (r = –0.75), methacholine (r = –0.74), peak flow variability (r = 0.59), and clinical asthma severity (r = 0.57). Eosinophils were the main granulocyte present in sputum and correlated with airway responsiveness to saline solution (r = –0.63) but not with other clinical markers of asthma severity. Bronchoalveolar lavage cell counts were not related to clinical asthma severity. Conclusions: In asthmatic patients treated with cortico-steroids, the dominant inflammatory effector cell in the epithelium is the metachromatic cell, and in sputum it is the eosinophil. These cells correlate with the degree of airway hyperresponsiveness. Clinical asthma severity correlates with airway responsiveness and epithelial metachromatic cells. Induced sputum eosinophils and airway responsiveness to hypertonic saline solution may be useful markers of airway inflammation for clinical practice. (J Allergy Clin Immunol 2000;105:752-9.)