This study was conducted to examine the effects of gonadotropins (PMSG and hCG) and estradio1-17β (E2) on the timing of nuclear maturation and cumulus mass expansion in pig oocytes cultured in vitro. Irrespective of the addition of hormones, the progression of meiosis to metaphase II was enhanced within 30 to 36 hr after culture. On the other hand, the proportion of oocytes reaching metaphase II was significantly increased by the addition of gonadotropins with or without E2 after 36 hr of culture (69-77%). High proportions of the oocytes with expansion of the whole cumulus mass were observed in the media containing PMSG within 30 to 36 hr after culture. However, most of cumulus mass had already formed monolayer after 24 hr of culture in the medium containing hCG alone or in the control medium without hormones. These results indi-cate that under our conditions, the progression of meiosis to metaphase II and cumulus mass expansion of pig oocytes cultured in vitro can be synchronously induced by 36 hr of culture in the media containing PMSG with or without E2.