OBJECTIVE Recently pure gonadotropins have become available through recombinant technology. In parallel with ongoing clinical trials it is important to examine the effects of these new gonadotropin preparations in experimental studies in human granulosa cells. In the present study the effects of recombinant FSH (rFSH) and LH (rLH) on steroid and inhibin production were examined in human granulosa cells in culture. METHODS Granulosa cells were obtained during the follicular phase of the menstrual cycle in seven women undergoing gynecological laparotomy and from follicles in stimulated cycles in women undergoing oocyte retrieval in connection with in vitro fertilization/embryo transfer. The granulosa cells were cultured in modified Medium 199 containing 1% fetal bovine serum for 4-8 days with and without hormones. Media were changed on alternate days and stored at -20 degrees C until analyzed for estradiol, progesterone and inhibin. RESULTS Granulosa cells from natural cycles were highly responsive to rFSH which caused a dose-related (rFSH 0.1 to 100 ng/ml) increase in estradiol and progesterone accumulation. The maximal stimulatory effect was reached with a concentration of rFSH between 1 and 10 ng/ml. Granulosa cells from stimulated cycles responded highly to rLH in terms of increased progesterone production during the whole culture period. A maximal stimulatory effect was observed with rLH at a concentration of 0.1 ng/ml. Both types of granulosa cells responded to recombinant gonadotropins in terms of increased inhibin production. CONCLUSIONS The present study demonstrates that granulosa cells from human ovarian follicles are highly responsive to recombinant gonadotropins as demonstrated by increased steroid and inhibin production.