The effects of mammalian gonadotropin-releasing hormone on ovarian release of progesterone, androgens and estradiol-17 beta were studied in vitro by a superfusion system carried out on follicles of adult female Rana esculenta, collected at different periods of the annual reproductive cycle. The follicles were superfused with medium alone, pituitary, mammalian gonadotropin-releasing hormone, or pituitary plus mammalian gonadotropin-releasing hormone. For follicles obtained in the prereproductive period, pituitary plus mammalian gonadotropin-releasing hormone increased the estradiol values much more than pituitary alone. In the reproductive period, pituitary alone increased the estradiol values much more than pituitary plus mammalian gonadotropin-releasing hormone. For follicles obtained in the recovery period, mammalian gonadotropin-releasing hormone alone stimulated the highest estradiol production, and pituitary plus mammalian gonadotropin-releasing hormone increased the estradiol values much more than pituitary alone. The results reported here suggest that mammalian gonadotropin-releasing hormone and/or pituitary have a direct effect on ovarian estradiol secretion, and that this effect varies with the annual reproductive cycle.