Nasal polyp (NP) is considered an inflammatory condition in nasal and paranasal sinus cavities and is frequently encountered in otolaryngology clinics. Although the pathophysiology of nasal polyps is poorly understood, it seems likely that the epithelium may play a critical role in the genesis of inflammatory nasal disease. The aim of this study was to investigate the role of free radicals and antioxidant enzymes in NP and compare these findings with concha bullosa (CB). NP and CB were obtained from 27 and 23 patients, respectively. Glutathione peroxidase (GSH-Px), catalase (CAT), xanthine oxidase (XO) total (enzymic plus non-enzymic) superoxide scavenger activity (TSSA), non-enzymic superoxide scavenger activity (NSSA), superoxide dismutase (SOD), and MDA levels in NP and CB were measured. GSH-Px activiy was significantly lower in patients with NP than in the CB group. However, CAT, XO activities and MDA levels were significantly higher in patients with NP than in the CB group, but TSSA, NSSA and SOD activities were unchanged. Increases in the levels of tissue MDA in patients with NP compared to the CB group may indicate the presence of free radical damage in patients with nasal NP. Copyright (c) 2005 John Wiley & Sons, Ltd.