A recent study suggested that protease-activated receptors (PARs) are involved in allergic respiratory diseases, such as asthma. Chronic rhinosinusitis (CRS) is one of the most common chronic airway diseases, but little is understood about its pathogenesis. The purpose of this study was to compare the expression and distribution of PARs in biopsy specimens obtained from CRS and control patients. Biopsy specimens were obtained from 7 pituitary tumor patients as controls, 8 CRS patients with aspirin-tolerant asthma (ATA), 7 CRS patients with aspirin-induced asthma (AIA), and 7 CRS patients without asthma (CRS). Sections were stained for PAR-1, PAR-2, PAR-3 and PAR-4 using specific polyclonal antibodies. Staining was scored semiquantitatively for both intensity and distribution. To confirm the presence of PARs on inflammatory cells, double staining with eosinophil cationic protein (EG2) and elastase was also performed. Both the epithelium and the infiltrating inflammatory cells in the CRS with asthma groups showed significant upregulation of the expression of PAR-2 and PAR-3 compared with the CRS without asthma group and the control group. In the patients with CRS complicated by asthma, eosinophils were increased among PAR-2- and PAR-3-positive cells. In the patients with CRS not complicated by asthma, neutrophils were increased among PAR-2-positive cells. Differences in the expression of PAR-2 and PAR-3 on epithelial cells, eosinophils and neutrophils may be involved in the pathogenesis of CRS. CRS may be able to be treated by targeting PAR-2 and PAR-3.