In a previous work we demonstrated the relationship between nerve fibers and nerve endings and interstitial cells (estrogen-producing cells) from the atrophic right ovary and the medulla in the left functioning ovary during embryogenesis in the chick, in ovo. Besides, the local production of neurotrophins by steroidogenic cells is probably involved in the control of ovarian innervation. The objective of the present study was to analyze ultrastructurally the innervation during the differentiation of chick ovary cultured with 17-beta-estradiol. Explants of right and left ovaries from seven to nineteen days in ovo development were cultured separately for 4 days in MEM (controls) or in the presence of 17-beta-estradiol (problems). In controls the electron microscopic examination of the innervation explants from chick embryo ovaries revealed that the interstitial cells are well innervated. Nerve fibres and nerve endings were observed in close contact with steroid-producing cells, a similar pattern of innervation that those of the fifteen days ovaries in ovo development. Problems cultured from seven days showed nerve fibres and nerve endings at difference to controls. These results in vitro suggest that innervation of the ovaries is controlled by indirect mechanism via the hypothalamic-pituitary system and local production factors. More experiments are necessary to confirm this results.