Recent data suggest that follicular fluid may play an important role in the endocrine balance of polycystic ovary syndrome, probably by acting on the theca-granulosa cell relationship. The aim of this study was to evaluate the effect of steroid-free follicular fluid on steroidal response and cell proliferation of human granulosa luteal cells from polycystic (POGC) and normal ovary (NC). Granulosa cells (from both POGC and NC) were cultured for 48 h with or without increasing dilutions of follicular fluid (FF) obtained from polycystic (FFp) and normo-ovulating (FFc) patients. Both follicular fluids were able to elicit aromatase activity as well as progesterone production and thymidine incorporation. POGC, when incubated with FFp, showed a lower increase of aromatase activity and progesterone production with respect to NC. Furthermore, the proliferation rate was increased by incubation with either follicular fluid, but the increase was less with FFp compared to FFc. Aromatase/[3H]thymidine (A/T) and progesterone/ [3H]thymidine (P/T) ratios could be considered to be representative of the contribution of the single cell unit to steroidogenesis. Using high concentrations of either follicular fluids, POGC showed a higher A/T ratio compared with NC. Moreover, the same treatment strongly decreased P/T ration in POGC, while it was ineffective in NC. Our study show that an abnormal interaction between POGC and their own follicular fluid can be implicated in the pathogenesis of the altered steroidal response in these cells, and that in particular it could affect the proliferation rate.