Infection and allergy have been known to play an important role in the pathogenesis of nasal polyps. Mast cells are believed to be a significant effector cells in nasal allergy and there has been many reports about the increase in number of mast cells in nasal polyps. This study was done to find out the exact distribution of mast cells in the nasal polyps by using new markers of mast cells such as cDNA of c-kit proto-oncogene, mast cell protease-6(MCP-6) and mast cell carboxypeptidase A(MC-CPA) for elucidating the pathogenesis of nasal polyps. Expression of c-kit gene was investigated by means of Northern blotting. C-kit transcripts gave a band of approaximately 5.5 Kb. The expression rate of c-kit mRNA transcript in polyp was much higher than that of normal nasal tissue. By in situ hybridization, the signals were observed specifically at the mast cells. Furthermore, nasal polyp-mast cells were found to differ from normal nasal tissue-mast cells in the expression of mast cell protease genes. The 1.1 Kb mRNA transcript for MCP-6 were detected in nasal polyp, whereas MCP-6 mRNA was not detected in normal nasal tissue. The 1.5 Kb mRNA transcripts for MC-CPA were also readily detectable in nasal polyps. These findings suggest that mast cells play an important role in development of nasal polyps.