There is increasing evidence for the role of basophils in the pathogenesis of bronchial asthma. To examine the presence of basophils in the airways of patients with fatal asthma by immunohistochemistry, we stained lung tissues from four post-mortem cases who had died from severe asthmatic attacks and four controls with a monoclonal antibody raised against tryptase (AA-1) and anti-IgE. Mast cells and basophils were identified in the bronchioles as A A-1- and anti-IgE-positive cells, and anti-IgE-posilive cells, respectively. Airway mast cells were found beneath the basemenl membrane, near blood vessels in the submucosa, and adjacent to the submucosal glands, and scattered throughout the muscle bundles. There was a significant increase of mast cells in the asthma group compared with the control group (203.5 ± 84.6/mm2, mean ± s. d. vs 37.7 ± 8.7/mm2, P < 0.05, n= 4). In contrast, basophils were observed in the airway lumen, in the bronchial epithelium and in the submucosa. The number of basophils in the bronchioles was 81.8 ± 55.5/mm2 (n= 4); however, basophils were not found at all in the airways of the control group. Although eosinophils, B lymphocytes and macro-phages bear low affinity IgE receptors and could react with anti-IgE, the location of these cells in the close sections did not correspond closely with basophils. The presence of basophils in lung tissues obtained from fatal asthma patients supports the view that basophils play a role in the pathogenesis of bronchial asthma.