To evaluate the roles of eosinophils in allergic rhinitis, eosinophil cationic protein (ECP) levels in sera and nasal secretions were measured in 28 patients with allergic rhinitis. In patients, blood eosinophil counts and serum ECP levels were significantly higher than in controls (p < 0.05). However, there was no statistically significant correlation between blood eosinophil count and serum ECP level (r = 0.025). The number of eosinophils and the ECP level in nasal secretion were also measured. In patients, the ECP level increased with the number of eosinophils, and the ECP level in nasal secretion was significantly higher than in controls (p < 0.05). These results suggest that eosinophils and ECP play important roles in allergic rhinitis.