Studies in animals have highlighted a possible role for growth factors, particularly IGF-I on cellular replication and cytodifferentiation in the ovary. At this time, few studies have been performed about IGF-I in the human ovary. From 38 women undergoing in Vitro Fertilization 293 antral fluids were collected and assessed for steroids (estradiol and progesterone), FSH and IGF-I. Two induction treatments were compared: clomiphene citrate/hMG (group A, N = 15), triptoreline/hMG (group B, N = 23). We also studied relationships between quantitative parameters and oocyte collection or oocyte corona cumulus complex maturity. In group B, the highest antral estradiol levels were found in follicles yielding an oocyte (p <0.05). Concerning antral progesterone, higher levels were observed in follicles collected from group A than in follicles collected from group B (p < 0.05); for this parameter, the highest levels were observed when an oocyte was harvested, whatever the treatment (p <0.05). Highest antral FSH levels were observed in group B (p <0.05). IGF-I levels were higher in follicles collected from group B than in follicles collected from group A (p <0.05) and antral IGF-I levels differed between mature and immature oocyte corona cumulus complex in group B (p <0.05). These results, which are in keeping with studies about biological action of IGF-I in animal or human follicles or granulosa cells, led us to hypothesize a role for IGF-I in human follicular recruitment and maturation, a role that possibly is enhanced during GnRH analogue and gonadotropin therapy.