Nasal polyp is a chronic inflammatory disease of the upper airways often associated with other respiratory disorders such as allergic rhinitis, sinusitis and asthma. Mast cell may be classified immunohistochemically by their protease contents and ultrastructually distingushed by granule morphology as MC_T and MC_TC. To investigate the distribution of mast cell subtypes in the nasal polyp, middle turbinate and inferior turbinate, We employed immunohistochemical double staining using mouse monoclonal antichymase antibodies and mouse monoclonal antitryptase antibodies. Nasal polyp, middle turbinate and inferior turbinate mucosa were obtained from 10 patients with chronic sinusitis associated with nasal polyp. Each tissues were fixed in Carnoy's solution and embedded in OCT. Mast cells were stained sequentially for biotin conjugated antichymase and alkaline phosphatase conjugated antitryptase. In nasal polyp, MC_T were predominant in epithelium and MC_TC were predominant in stroma. In turbinate mucosa, MC_T were predominant in epithelium and MC_T were predominant in stroma. In turbinate mucosa, MC_T were predominant in epithelium and MC_TC werepredominant in stroma. Total number of mast cells and especially MC_T in nasal polyp were more numerous than in turbinate mucosa. In conclusion, mast cells, especially, MC_T, increased at epithelium and stroma in nasal polyps and may be a critical factor of pathogenesis in formation and growth of nasal polyp.