Allergy has been reported as an important factor in the etiology of nasal polyposis. Asthma, chronic sinusitis and aspirin hypersensitivity are frequently found together with nasal polyposis. Total IgE, RAST for specific IgE and skin prick test were used to investigate the incidence of allergy in 95 patients with nasal polyposis. In addition, histopathologic appearance of polyp tissue was examined in 21 patients after polypectomy and compared in allergic and nonallergic groups. IgG subclass levels were also measured to detect if there were any changes. Mean serum IgE level was found to be higher in the patient group and the skin prick test (SPT) was positive in 66.3% of patients. On the basis of positive SPT and serum RAST results, 45.2% of all patients with nasal polyposis were defined as allergic. Both total IgE and IgG, were detected at increased levels in the SPT-positive group. These findings suggest that an IgE-mediated mechanism may be present in a subpopulation of patients with nasal polyposis.