Ovulation resembles a tissue remodeling process such as a blood coagulation. The present study was aimed to examine the involvement of tissue factor, a primary factor for extrinsic coagulation pathway, in the ovulation. Northern blot analysis revealed that mRNA levels of tissue factor and tissue factor pathway inhibitor 2 (TFPI-2) in the ovary were stimulated by human chorionic gonadotropin (hCG) treatment in surperovulation model, of immature rats. Real-time PCR analysis demonstrated that the expression of tissue factor and TFPI-2 was stimulated in granulosa and theca cells of preovulatory follicles, respectively. The induction of tissue factor mRNA was blocked by the progesterone receptor antagonist RU486. Tissue factor protein was not detected in the ovary by Western blot and immunohistochemical analysis due to the lack of a specific antibody. Interestingly, the levels of tissue factor and TFPI-2 mRNA were increased in the ovarian cells of rats induced ovarian hyperstimulation syndrome (OHSS) and in granulosa cells of OHSS patients undergiong in vitro fertilization. The present findings indicate the stimulation of tissue factor system during ovulation, and in OHSS patients, implicating the possible involvement of tissue factor system in OHSS.