1. Objectives Polycystic ovary syndrome (PCOS) is characterized by chronic anovulation and hyperandrogenism and affects approximately 5–10% of women of reproductive age. In vitro maturation (IVM) of mammalian oocytes has become an efficient method to produce mature oocytes in order to use in assisted reproductive techniques such as in vitro fertilization (IVF), intra cytoplasmic sperm injection (ICSI), and cloning. In some mammals, oocytes maturation and its progression to metaphase II are steroid–dependent. Progesterone exists in the follicular fluid that contributes to normal mammalian ovarian function. It has been shown that, in vivo levels of progesterone in follicular fluid are closely associated with developmental competence of an oocyte. In PCOS, progesterone secretion and levels in ovary and follicular fluid is low. In this study, we examined the effects of progesterone on in vitro maturation of oocytes derived from polycystic ovary in mouse.  Induction of PCO PCO was induced in female NMRI mice 6-8 weeks- old with daily administration of testosterone enantate (1 mg/100 g body weight) for 1 to 4 weeks.Control mice were injected with vehicle alone. The Effect of Progesterone on the In Vitro Maturation of Mouse Germinal Vesicle Oocytes Derived from Polycystic Ovary A. Bazdar 1, M. Azadbakht 1, H. Nojomi 2 1 Department of Biology, Faculty of Science, Razi University, Kermanshah, Iran 2 Department of Obstetrics and Gynecology, Bistoon Hospital, Kermanshah, Iran Methods Results  Oocyte In Vitro Maturation o The ovaries were dissected and intact antral follicles were selected. o Immature oocytes (germinal vesicle oocytes) were matured in modified medium α-MEM containing combinations of 5% FBS, 100 mIU/ml rFSH (Gonal-f), 10 ng/ml rEGF, 7.5 IU/ml HCG with progesterone (3 mg/ml), (treatment I) and without progesterone(treatment II) for 24h. o The number of oocytes at the germinal vesicle (GV), germinal vesicle breakdown (GVBD) and metaphase II (MII) stages were counted. o Immature oocytes assigned to two groups. group I, PCO and group II, non-PCO There were two treatments in each group. treatment I with progesterone treatment II without progesterone Conclusion  These findings suggest that supplementation of culture medium with progesterone have an positive effect on oocyte in vitro maturation from polycystic ovaries.  Recent data demonstrate links between culture conditions and oocyte maturation in PCO and suggest that a strategies to optimize developmental competence of PCO oocytes should target correction of the oocyte development process. GroupsTreatmentsNo.GVGVBDMIIDEG. Exp. I14113(%9.22) b 29(%20.57) a 70(%49.65) a 29(%20.57) a II13429 (%21.64) a 25 (%18.66) a 26(%19.4) b 54 (%40.3) b Control I10913(%12) a 28(%25.7) a 28(%25.7) b 40(%36.5) b II14824 (%16.22) a 43 (%29.05) a 18 (%12.16) b 63(%42.57) a Table 1. Effect of progesterone on in vitro maturation of oocyte after 24h. Exp. : with testosterone enantate injected Control :without testosterone enantate injected Treatment I : with Progesterone Treatment II : without Progesterone GV: Germinal Vesicle, GVBD: Germinal Vesicle Break Down, MII: Metaphase II, DEG: degeneration a/b Values within columns with different superscripts are significantly different (ANOVA, P < 0.05) b a a a b a a a a b b a a b b a Figure 1. Effect of progesterone on in vitro maturation of oocyte after 24h. Exp. : with testosterone enantate injected Control :without testosterone enantate injected Treatment I : with Progesterone Treatment II : without Progesterone GV: Germinal Vesicle, GVBD: Germinal Vesicle Break Down, MII: Metaphase II, DEG: degeneration a/b Values within columns with different superscripts are significantly different (ANOVA, P < 0.05)