Nasal polyposis (NP) is a chronic inflammatory disease of the nasal mucosa. The etiology and formation of NP are still not elucidated and have been debated for many years. The objective of the present study was to investigate the role of nasal allergy in the development of NP. The following aspects were analyzed: age, sex, and patient's symptoms; correlation between asthma, aspirin intolerance, and NP; serum immunoglobulin levels and eosinophilia; and concentration of interleukins 1 beta, 3, and 4 in NP. Thirty-nine patients with NP were selected 13 of them allergic and 26 non-allergic. A control group of 11 individuals was also studied. The concentrations of interleukins 1 beta, 3, and 4 were measured by enzyme-linked immunosorbent assay (ELISA). There was a higher incidence of NP after the fourth decade of life and among men. We found no correlation of asthma or aspirin intolerance with the presence or absence of allergy. Serum levels of IgE and eosinophils were significantly higher in patients with allergy and NP and the concentrations of interleukins 3 and 4 were positively correlated with NP. There was no difference in interleukin 3 and 4 concentration between the non-allergic group with NP and the control group, suggesting that these interleukins do not play an important role in the etiology and formation of NP. These results suggest that the immunologic pathway involved in the etiology of NIP is different from the one correlated with allergy (IgE-mediated).