We have examined the effects of IL-6 and bFGF on growth and reductive 17 beta-hydroxysteroid dehydrogenase (17-HSD) activity in a human ovarian cell line A2780 under defined culture conditions (standard RPMI (GM+PHR), phenol red-free RPMI (GM-PHR), or GM-PHR supplemented with 17 beta-estradiol). In media GM+PHR, neither factor influenced terminal cell density. However there was a 2-fold stimulation in 17-HSD activity (E1- > E2) in the presence of IL-6 and a 3-fold increase in the presence of bFGF. Cells cultured GM-PHR showed a 25-30% reduction in terminal cell density compared with cells cultured GM+PHR, and addition of factors resulted in a modest reduction (10-15%) in cell growth, with no detectable changes in 17-HSD. Addition of 17 beta-estradiol to GM-PHR cultures increased terminal cell density by up to 3-fold, with no effect on 17-HSD, and when combined with IL-6 or bFGF, a synergistic effect on growth was observed, but 17-HSD levels were unchanged. Our results suggest that cultured ovarian tumour cells respond to paracrine factors likely to be present in the ovary in vitro, and there is a possible interactive effect of estromedins with these factors.