BACKGROUND: There are limited data about the levels of soluble apoptotic factors and their modulation with therapeutic regimens in IVF cycles. The aim of the current study was to determine follicular fluid, and serum levels of soluble Fas (sFas) and soluble Fas ligand (sFasL) in PCOS patients undergoing IVF/ICSI cycles; also to investigate the effects of metformin on these factors and on apoptosis of luteinized granulosa cells. METHODS: We investigated the serum and follicular fluid levels of sFas and sFasL in patients with PCOS (n=28) and compared them with those of the patients with infertility due to male factor (n=12) undergoing IVF cycles. Effects of metformin therapy on these parameters and apoptosis of luteinized granulosa cells were also investigated among the patients with PCOS. RESULTS: Serum levels of sFas were significantly lower in the PCOS group compared to those in women with infertility due to male factor. Metformin therapy in PCOS patients preceding IVF cycles increased serum levels of sFas and decreased follicular fluid levels of sFasL compared to those on placebo. Follicular fluid from PCOS patients demonstrated luteinized granulosa cell DNA fragmentation in agarose gel, whereas a similar pattern was not observed among PCOS patients undergoing metformin therapy. CONCLUSION: Decreased serum levels of sFas and luteinized granulosa cell DNA fragmentation is observed in patients with PCOS undergoing IVF cycles. Metformin therapy preceding IVF demonstrates an antiapoptotic effect with increased serum levels of sFas, decreased follicular fluid levels of sFasL and prevention of luteinized granulosa cell DNA fragmentation.