|The purpose of this study was to investigate the effects of gonadotropin and nitric oxide (NO) on the expression of mouse follicular bad and bax genes that are known to induce apoptosis. Large and medium size follicles of immature mice were obtained at 0, 24, and 48 hours time intervals after Pregnant Mare뭩 Serum Gonadotropins (PMSG, 5 I.U. ) injection. Preovulatory follicles collected at 24 hrs after PMSG injection were cultured with or without various chemicals such as gonadotropin, Gonadotropin Releasing hormone (GnRH), testosterone, Sodium nitroprusside (SNP) for 24 hrs at 37캜. After 24 hrs culture, the culture media was used for nitrite assay and total RNA was extracted, subjected to RT-PCR for the analyses of bad and bax expression. We found that expression of bad and bax genes in follicles was markedly reduced before and after in viva priming with hCG. When the preovulatory follicles were cul-tured for 24 hrs in culture media with PMSG and hCG, the expression of bad and bax genes was decreased. Moreover, SNP (NO generating agent) can significantly suppress the expression of bad and bax genes in follicles when apoptosis was induced by GnRH agonist and testosterone, At the same time, nitrite production of culture media was increased in GnRH agonist + SNP, testosterone + SNP and SNP treated groups than control group. These data demonstrated for the first time that peptide hormones and NO may play imrtant roles in the regulation of mouse follicular differentiation and may prevent apoptosis via suppressing the expression of bad and bax genes.