Numerous theories have been proposed concerning the etiology and mechanism about formation of nasal polyp. These include allergy, infection of the nose and paranasal sinus and dysfunction of autonomic nervous system. None of these is established of universally accepted. Auther observed the distribution of the tissue mast cells in 30 cases of nasal polyp (8 cases with allergic rhinitis, 22 cases without allergic rhinitis) and in nasal mucosa of 10 cases of control. The tissue was fixed with Mota's basic lead acetate solution or 10% formalin solution and stained with 0.5% toluidine blue(ph 4). The results were as follows : 1) The number of the mast cells at fixing with Mota's solution was greater than that of formaline solution in nasal polyp with or without allergic rhinitis and the normal control. 2) The number of the mast cells in nasal polyp group was greater than that of the normal control group in all layers. 3) After fixing with Mota's solution, the number of the mast cell in the epithelium of nasal polyp with allergic rhinitis was greater than that of nasal polyp without allergic rhinitis. 4) In the number of the mast cell in lamina propria, around gland and blood vessel of nasal polyp, it was not significant difference between polyp with and without allergic rhinitis. 5) The size of mast cell at fixing with formalin solution was larger than that with Mota's solution(p<0.01). It was considered that mast cells in lamina propria, around gland and blood vessel were related to the formation of nasal polyp, and allergic rhinitis was associated with mast cells in epithelium.