The follicular fluid (FF) content of androgens, estrogens and epidermal growth factor (EGF) has been evaluated in a group of patients with policystic ovary disease (PCO) and in one of normally-ovulating infertile women (NOW) in an IVF/ET program. The in vitro response to follicle-stimulating hormone (FSH) has been also evaluated in granulosa luteal cells from the same patients. PCO patients showed significantly higher FF androstenedione (delta 4) and testosterone (T) and similar FF estrone (E1) and 17 beta-estradiol (E2) levels compared to controls. In vitro production of E1 and E2 by granulosa luteal cells from PCO patients and from controls were overlapping and their response to FSH was similar. These data indicate a normal intrinsic potential aromatase activity in ovaries from PCO patients stimulated with gonadotropins and suggest that PCOs do not derive from inherent ovarian aromatase deficiency. Increased FF androgen content following gonadotropin stimulation may result from theca cell hyperactivity and androgen accumulation in the follicular antrum of rescued hyperandrogenic follicles as well as from inhibitory factors that may inhibit aromatase activation in vivo, partially counteracting the effect of gonadotropins. FF EGF levels were significantly higher in the group of PCO patients compared to those of NOW. EGF may play a role in blunting the in vivo response of granulosa cells to gonadotropins.