Mast cells contribute to the pathophysiology of asthma through their immunomediator-secretory activity in response to both immunological and nonimmunological stimuli, and infiltrate the bronchial epithelium in this disease. We hypothesized that human lung mast cells (HLMC) localize to the bronchial epithelium via a specific cell-cell adhesion mechanism. We investigated the adhesion of HLMC to primary bronchial epithelial cells and the bronchial epithelial cell line BEAS-2B. HLMC adhered avidly to both primary cultures of bronchial epithelial cells and BEAS-2B cells (mean adhesion 68.4 and 60.1%, respectively) compared with eosinophil adhesion to BEAS-2B (mean adhesion 10.3%). HLMC adhesion did not alter after epithelial activation with cytokines, did not require Ca2+, and was not integrin-mediated. IgE-dependent activation of HLMC produced an approximately 40% inhibition of adhesion. There was significant attenuation of adhesion after incubation of HLMC with pronase, beta-galactosidase, and endo-alpha-N-acetylgalactosaminidase, indicating that HLMC adhere to bronchial epithelial cells via galactose-bearing carbohydrates expressed on a cell-surface peptide(s).