Drug resistance in ovarian cancer treatment urges the exploration of new targets for drugs against this malignancy. Fas is a cell membrane receptor which, after engagement with Fas ligand (FasL), triggers apoptotic death. In this study Fas and FasL levels in cyst fluids and sera of patients with benign, borderline and malignant ovarian tumors and in corresponding tumors are determined. Fas and FasL were determinded by ELISA and immunohistochemistry in 30 patients with benign, 5 patients with borderline and 24 patients with malignant epithelial ovarian tumors. In serum there were no differences in median Fas levels, while median FasL levels were higher in healthy women (p=0.02). In malignant cyst fluids, median Fas levels where higher compared to benign cyst fluids (p<0.01). FasL immunostaining was more frequent in malignant ovarian tumors (p=0.002). In conclusion, serum Fas or FasL levels do not seem useful markers. Elevated Fas and equal FasL levels in malignant cyst fluids, suggest an increased production of Fas, and not of FasL by malignant cells. High expression of both Fas and FasL, in malignant ovarian tumors present Fas/FasL as an interesting route to explore for innovative cancer therapy.