Introduction:
Data on the possible role of peritoneal fluid free radical-mediated oxidative damage in the pathogenesis of endometriosis still remains inconsistent. The aim of the study was to determine iron metabolism markers and their influence on oxidative stress arameters in the peritoneal fluid of women with endometriosis.

Material and Methods:
110 women with endometriosis and 119 patients with benign ovarian cysts were included in the study. All visible peritoneal fluid was aspirated during laparoscopy from the anterior and posterior cul-de-sacs. under direct vision to avoid blood contamination. Haemoglobin, iron, total oxidative status, and total antioxidant status were measured using standard colourimetric kits.

Results:
Haemoglobin, iron levels, as well as total oxidative status values were significantly higher, whereas total antioxidant status values were significantly lower in the peritoneal fluid of patients with endometriosis, in comparison to the reference groups. No differences were observed in peritoneal fluid concentrations of all parameters measured in relation to the phase of the menstrual cycle.

Conclusions:
Peritoneal fluid of women with endometriosis is characterized by disrupted iron metabolism. This is most likely related to an increased number of erythrocytes in the peritoneal cavity of endometriotic women, which leads to a higher concentration of haemoglobin in this environment. Impaired iron homeostasis may have a significant influence on the pathophysiology of peritoneal endometriosis by the direct impact of haemoglobin derivatives and/or formation of the pro-inflammatory and pro-oxidative environment. Peritoneal cavity oxidative stress occurs predominantly in women in advanced stages of the disease.