To determine the steroidogenic capacity of follicular and cultured granulosa cells, estradiol and progesterone productions were studied in 10 fertilized and 10 nonfertilized IVF-ET cases. After separation of granulosa cells, they were cultured in EBSS within 24 hours. Follicular fluid obtained from follicles with fertilized oocytes contained higher levels of estradiol (E2), progesterone (P) and P/E2 ratio although the differences were statistically nonsignificant. Cultured granulosa cells demonstrated higher numbers per mililiter in fertilized oocyte group in comparison with the nonfertilized ones (p<0.05). However, nonfertilized group showed higher estradiol and progesterone production per 10 million granulosa cells (p<0.05) while P/E2 production rate of cultured granulosa cells was higher than the P/E2 ratio of fertilized group (p<0.05). These results suggest that preovulatory granulosa cell steroid production in favor of progesterone may deteriorate fertilization.