Respiratory epithelial mast cells are an expression of airway inflammatory processes. Nasal epithelial mast cells are known to be increased in allergic rhinitis and have now been examined in patients with nasal polyps. Metachromatic cell counts (mean +/- standard error) expressed as the sum of large mast cells, atypical mast cells and basophils in epithelial scrapings of the inferior turbinates, assessed after Carnoy's fixation and toluidine blue staining (pH 0.5), were 37.5 +/- 29 in non-allergic normal control subjects (n = 11), 435 +/- 130 in polyp patients who were allergic (n = 18), and 699 +/- 267 in polyp patients who were not allergic (n = 8). Metachromatic cell counts in epithelial scrapings obtained in vivo from nasal polyps of allergic patients (n = 8) were 1769 +/- 962, and 2308 +/- 1544 from polyps of non-allergic patients (n = 5); metachromatic counts were 2089 +/- 633 in epithelial scrapings from excised polyps of allergic patients (n = 14) and 2214 +/- 640 from polyps of non-allergic patients (n = 13). It is concluded that the number of metachromatic cells in the epithelium of nasal polyps and the adjacent nasal mucosa is elevated compared with normal nasal epithelium and the increased number does not depend upon allergy.