The inflammatory cell infiltrate in bronchial biopsies of 12 aspirin-sensitive asthmatic (ASA) subjects and eight non-aspirin-sensitive (non-ASA) control subjects have been compared. Biopsies were taken from a right middle or lower lobe segmental carina using fiberoptic bronchoscopy. The biopsies were snap-frozen in OCT, and sections 5 microns thick were doubled immunostained using a rabbit polyclonal antibody to the enzyme 5-lipoxygenase (5-LO) and with a monoclonal antibody to neutrophils (NP57), macrophages (EMB11), and total (BMK13) and activated eosinophils (EG2), mast cells (AA1), and T-lymphocytes (anti-CD3). There was no significant difference in the total numbers of cells staining for 5-LO between the two groups of subjects. As a percentage of total 5-LO cells, there were significantly more mast cells (12.9 +/- 3.8% versus 3.4 +/- 3.1%; p = 0.039) and total eosinophils (34.7 +/- 9.4% versus 11.1 +/- 3.8%; p = 0.044) and significantly fewer macrophages (23.3 +/- 6.1% versus 39.8% +/- 5.3; p = 0.041) in the bronchial biopsies from ASA subjects as compared with non-ASA patients. The numbers of neutrophils, T-lymphocytes, and activated eosinophils were similar for the two groups. The increased numbers of eosinophils and mast cells identified in the bronchial tissue from aspirin-sensitive asthmatic subjects may be the source of the enhanced cysteinyl leukotriene production observed in these subjects.