The superoxide anion, hydrogen peroxide, and hydroxyl radical are oxygen free radicals which arise in cell metabolism and which are toxic to cells, with an important role in carcinogenesis. The measurement of the oxygen free radical is a problem due to the instantaneously changing nature, and therefore the superoxide dismutase(SOD) is employed which act as an oxygen free radical scavenger. The authors quantitatively analyzed the SOD levels in normal uterine cervix epithelium, cervical intraepithelial neoplasia, and in invasive cervical cancer patients by the SOD-525R spectrophotometric assay and compared the results between each group with respect to prognostic variables such as stage of disease, cell type, lymph node involvement, and SCC Ag(TA-4 Ag) levels. The mean SOD levels were 0.41U/ml, 0.39U/ml and 0.73U/ml in the normal uterine cervix, intraepithelial neoplasia, and invasive cervical cancer groups, respectively, showing statistically significant difference by the Oneway anova test(p=0.05). The mean SOD levels according to the stage of disease were 0.5U/ml, 0.62U/ml, and 1. 15U/ml for stages I a, I b, and stage II and above(p=0.029). For the cell type the SOD levels were 0.77/ml for squamous cell carcinoma and 0.57U/ml for adenocarcinoma(p=0.15). For cancer cell lymph node involvement cases, the mean SOD levels were 0.75U/ml and 0.57U/ml for lymph node involvement and no involvement respectively(p=NS). The mean SOD levels also did not show any significance when compared with SCC Ag levels where SOD was 0.78U/ml for SCC Ag levels of more than 2.0ng/ml, and 0.77U/ml for SCC Ag levels of less than 2.0ng/ml. From the above results the authors conclude that SOD levels were higher in invasive cervical cancer tissues compared to intraepithelial neoplasia and normal cervical tissues, that SOD levels increased with higher stage of disease, and that there was no relationship between SOD levels and known prognostic variables such as cell type, lymph node involvement and SCC Ag level.