The effects of epimestrol (5 mg every 6 hours for 5 days) on basal levels of luteinizing hormone (LH), follicle-stimulating hormone (FSH), prolactin (Prl), estradiol, progesterone, and dehydroepiandrosterone sulfate, and on the response to LH-releasing hormone (LH-RH) and thyrotropin-releasing hormone (TRH) stimulation, were studied in 18 cases of secondary amenorrhea and oligomenorrhea of hypothalamic-pituitary origin, in three cases of anorexia nervosa, in two cases of long-lasting progestin-induced amenorrhea, and in one case of precocious menopause. The results in the first 18 patients indicate that epimestrol treatment induces a significant increase in LH and Prl levels after 24 hours, while the FSH increase becomes significant only after 4 days of therapy. Twelve hours after discontinuation of treatment, all three hormone levels decreased significantly to values similar to the basal levels, while the pituitary response to LH-RH indicated a much more marked LH secretion than before treatment. A second test, performed 36 hours after the last drug administration, again showed a significantly higher LH response than that found under basal conditions. No significant variations were observed in the FSH response to LH-RH, nor in the Prl response to TRH. These data suggest that epimestrol interferes at the level of the centers responsible for Prl and gonadotropin secretion in the manner of a weak estrogen.