Nasal polyps are the most common mass lesion of the nasal cavity. Various pathogenetic mechanisms have been proposed. However, the cause is still largely unknown, and treatment methods have not been changed for several hundred years. In order to investigate the role of cytokines in the pathogenesis of nasal polyps, expression of cytokine messenger RNAs (mRNAs) in nasal polyps was investigated. We performed reverse transcriptase-polymerase chain reaction and Southern blot to examine gene expression of the cytokines interleukin (IL)-1 beta, IL-6, IL-8, transforming growth factor (TGF)-beta, IL-4, IL-5, and interferon (IFN)-gamma and compared the results with the gene expressions of these cytokines in normal nasal mucosa. Nasal polyp tissues were obtained from 14 patients undergoing polypectomy for nasal obstruction. Among them, 4 patients suffered from associated perennial allergic rhinitis. The mRNAs of IL-4 and IL-5 (Th2 cytokines) as well as IFN-gamma (Th1 cytokine) were expressed in all of the nasal polyps obtained from the 14 patients, irrespective of the presence or absence of allergy, while 2, 0, and 4 of 6 normal turbinate mucosae expressed IL-4, IL-5, and IFN-gamma mRNAs, respectively. The mRNAs of IL-1 beta, IL-6, IL-8, and TGF-beta were expressed in 6, 1, 2, and 3 of 6 normal turbinate mucosae, respectively, while the mRNAs of these cytokines were expressed in all of the 14 polyp tissues except IL-6 mRNA, which was expressed in 13 nasal polyp tissues. There were no differences in the mean density ratios of each cytokine band on Southern blot between polyp tissues with allergy and those without allergy. These results suggest that many cytokines are produced in nasal polyps, that they may play important roles in the pathogenesis of nasal polyps, and that allergy per se may not play a fundamental role in the pathogenesis of nasal polyps.