To investigate the expression of cytokine mRNAs in nasal polyps and the role of allergy in the pathogenesis of nasal polyposis, we studied the expression of IL-4, IL-5, and IFN-gamma mRNAs using the RT-PCR and Southern blot. Nasal polyp specimens were obtained from 14 patients with infectious rhinitis and 5 patients with perennial allergic rhinitis. Turbinate mucosa specimens were obtained from 10 patients with allergic rhinitis and from 10 healthy subjects as controls. IL-4, IL-5 and IFN-gamma mRNA were expressed in most specimens of allergic turbinate mucosa. The expression of these cytokines was less frequent in normal healthy turbinate mucosa. The density ratios of IL-4, IL-5 and IFN-gamma to beta-actin were individually determined in both polyp and turbinate tissues. The density ratio for each cytokine was relatively higher in polyp tissues than in healthy turbinate mucosa; however, there was no significant difference in the density ratios determined for polyps associated with allergic rhinitis as compared with polyps associated with infectious rhinitis. These findings indicate that nasal polyposis may differ from allergic rhinitis in the mechanism by which IL-4 and IL-5 are increased. It is concluded that allergy may have an insignificant role in the development of nasal polyps.