The effect of a single injection of dihydrotestosterone, testosterone, testosterone propionate, estradiol-17β or estradiol benzoate on serum levels of luteinizing hormone, follicle stimulating hormone and prolactin was studied in ovariectomized ewes. Luteinizing hormone levels increased following treatment with E, EB or TP, prolactin levels increased following treatment with E, EB, T or TP while FSH levels decreased after treatment with either E or EB. Free steroids appeared to produce earlier responses in hormone levels than the corresponding esters. Key words: Androgens, estrogens, gonadotropins, prolactin, ewes.