Many previous investigators have utilized mechanical rubbing as a method for examining effects of epithelial removal. In the present study, we examined whether this procedure also affects mast cell integrity in the underlying lamina propria. We isolated bronchial rings from six ferrets, and we found that removal of epithelium by rubbing decreased the total number of intact mast cells from 10.0 +/- 1.9 to 2.2 +/- 0.6 (SE) mast cells/mm luminal perimeter (P less than 0.01). In addition, we found a very large number of metachromatic particles that appeared to be mast cell granules unassociated with identifiable mast cells. Their identity was confirmed the presence of free mast cell granules and showed that they contained intact membranes. These effects were not observed when the epithelium was removed by enzymatic digestion, but they were observed after mechanical deformation of the bronchi alone. We suggest that mast cell components released by removing or damaging the epithelium may affect the function of various cells in the airway.