Recently, our laboratory has shown that gonadotropin-releasing hormone (GnRH) mRNA is present in the ovarian tissues (Int`l Congr. Endocr. Abst. No. 03-019-048, Kyoto, 1988). In the present study, we examine the changes in ovarian GnRH mRNA and its relationship with alteration in luteinizing hormone (LH), ovarian estradiol content, and hypothalamic GnRH mRNA in response to treatment of PMSG and/or hCG. The level of ovarian GnRH mRNA was increased 4-fold after stimulation of immature rats with 30 IT PMSG and remained a similar level later on. When hCG (10 IU) was injected to PMSG (10 IU)-primed rats 48 h later, the ovarian GnRH mRNA was clearly augmented 20-fold over the control values. Serum LH was induced endogenous LH surge in the combination of PMSG and hCG and significantly correlated with ovarian GnRH mRNA. Changes in estradiol content following PMSG treatment was also correlated with alteration in ovarian GnRH content. However, there is no strong correlation in changes of ovarian GnRH mRNA with hypothalamic GnRH mRNA. These data suggest that the changes in intraovarian GnRH gene expression appear to be involved in the ovulation process.