This study was designed to determine the activities of superoxide dismutase and glutathione peroxidase and some of the lipid peroxidation indices (malondialdehyde and total sulfhydryl groups) in eutopic and ectopic endometria of patients with endometriosis. Ectopic endometrial tissues (ovarian cysts; n=22) were obtained laparoscopically during the preovulatory period. Statistical analyses were made using the Wilcoxon signed-rank test. The levels of malondialdehyde and total sulfhydryl groups were similar in the eutopic and ectopic endometria, whereas the superoxide dismutase activity was found to be significantly higher in the latter (1,893+/-780 vs. 3,512+/-1,502 U/g protein; p=0.002). Although the glutathione peroxidase activity was slightly lower in the ectopic than in the eutopic tissues, the difference was not found to be statistically significant. The malondialdehyde levels were positively correlated with the plasma 17beta- estradiol concentrations in the ectopic endometria (r=0.683, p=0.001). No such correlation was seen in the eutopic tissue. It is suggested that various factors, such as cytokines released by activated macrophages in the peritoneal fluid and 17beta- estradiol itself synthesized by the ovaries, may locally affect the oxidant status of ectopic endometria. Copyright (C) 2004 S. Karger AG, Basel.