Quantitative analysis of sialic acid, L-fucose, elastase and albumin in the post-nasal drip of patients with chronic sinusitis was performed. Sixty-five cases of post-nasal drip were collected from patients with chronic sinusitis, aged 16-88 years old. The patients were classified into two groups: i. e. nonallergic group (n=58, without allergic rhinitis), and allergic rhinitis group (n=7, with allergic rhinitis). Additionally four cases of post-nasal drip obtained from patients with acute sinusitis were examined.<br>The mean concentration of sialic acid in the post-nasal drip from allergic rhinitis group (625-1850μg/ml) was significantly lower than that of acute sinsitis group (85-7094μg/ml). However, there was no significant difference in the mean concentration of sialic acid in the post-nasal drip between acute sinusitis and nonallergic group (85-7094μg/ml). The mean concentration of L-fucose in the post-nasal drip showed no significant differences in the groups of acute sinusitis (359-567μg/ml), nonallergic group (33-33312μg/ml) and allergic group (166-2842μg/ml). The concentration ratios of sialic acid to fucose (S/F) in the post-nasal drip either nonallergic or allergic group were significantly lower than that of acute sinusitis. The activity of elastase in the post-nasal drip from nonallergic group was significantly lower than that of acute sinusitis. The mean concentration of albumin in the post-nasal drip in three groups showed statistically no significant difference.<br>In 8 cases with nonallergic group and in 4 cases with allergic group the analysis of the S/F ratio was performed before and after the administration of antibiotics. In five cases with nonallergic group of which the treatment were effective, the S/F ratio was lowerd significantly after the drug administration. These findings suggest that the S/F ratio may be an impotant index for understanding the condition of chronic sinusitis.