Recently, epidemiologic and experimental studies have been reported that long-term macrolides are effective for the treatment of chronic airway inflammatory diseases including diffuse panbronchiolitis, chronic rhinosinusitis, and cystic fibrosis (Jaffe A, Francis J, Rosenthal M, et al. Long-term azithromycin may improve lung function in children with cystic fibrosis. Lancet 351:420, 1998), and that macrolides can directly reduce the production of IL-8 by nasal epithelial cells (Suzuki H, Shimomura A, Ikeda K, et al. Inhibitory effect of macrolides on interleukin-8 secretion from cultured human nasal epithelial cells. Laryngoscope 107:1661-1666, 1997). In this study we administered macrolides with 14-membered rings to patients with nasal polyps due to chronic rhinosinusitis for at least 3 months and measured the IL-8 level in nasal lavage from those patients. The IL-8 levels in nasal lavage from patients with nasal polyps were reduced during macrolide treatment. There was significant correlation between decreased IL-8 levels in nasal lavage and the clinical effect of macrolides on the size of the nasal polyps. In the group whose polyps were reduced in size, the IL-8 levels dramatically decreased from 231.2 pg/mL to 44.0 pg/mL (p < 0.05), and were significantly higher before macrolide treatment than those in the group whose polyps showed no change (p < 0.005). This reduction in IL-8 may be an important aspect of the effect of macrolide treatment on nasal polyps in chronic rhinosinusitis.