The two main theories about nasal polyp formation are allergic and infectious, but the exact pathogenesis of nasal polyps is not completely understood in spite of many studies. Recently multifactorial etiologic factors including immune reaction are proposed. Reactive oxygen species (ROS) which are chemically highly reactive, unstable and cytotoxic participate in various pathologic condition and there is no study about ROS for the pathogenesis of nasal polyps. The purpose of this study is to know that superoxide free radicals (one of ROS) play a role in the pathogenesis of nasal polyps from a viewpoint of the histopathological similarity between nasal polyps by epithelial rupture theory and superoxide-mediated tissue damage by inflammation and postischemia. Thirty patients (30 specimens) who received endoscopic intranasal surgery due to chronic paranasal sinusitis with polyps were included for the measurement of superoxide free radical production and xanthine oxidase (main enzyme for superoxide free radical production) activity in polyp group (25 specimen) and control group (5 specimen ; normal appearing nasal mucosa). The amount of superoxide free radical production increased 3 times(p<0.01) and the activity of xanthine oxidase 2 times higher in the polyp group respectively than those of the control group. These result suggests that superoxide free radicals play an important role in the pathogenesis of nasal polyps, also I propose the possible mechanism of nasal polyp formation.