We investigated the role of basophils and mast cells in the pathogenesis of bronchial asthma. Eight asthmatics (6 atopic, 2 nonatopic) and 6 control subjects were enrolled in this study. Bronchial responsiveness to acetylcholine (PC20ACh) was measured in asthmatics and endobronchial biopsy from right upper lobe bronchus was performed on the same day. Basophils and mast cells in the airways were identified by immunohistochemistry using a monoclonal antibody against tryptase and anti-IgE. The number of basophils of asthmatics was 52.2 +/- 12.5/mm(2). In contrast, no basophils were found in the airways of control subjects. There was a significant increase of number of mast cells in the asthma group compared to the control group (168.6 +/- 32.6 vs. 22.3 +/- 6.1, p<0.01). There was an inverse correlation between airway basophil and mast cell numbers and PC20ACh (r=-0.82, r=0.72, p<0.05). These findings suggest a possible role for basophils and mast cells in the pathophysiology of asthma.