OBJECTIVE We studied changes in pituitary response to GnRH during the luteal-follicular transition of the human menstrual cycle. METHODS Normally cycling women were investigated during two consecutive menstrual cycles. In each woman, GnRH tests were performed during the two LH surges and several times during the luteal-follicular transition. Data for analysis were available in all women on days -8, -6, -4, -2, -1, 1, 2, 3, 4, 5 and 7 in relation to the onset of second menstruation (day 1). METHODS Five normally ovulating parous women were studied. METHODS Pituitary response to GnRH was calculated as the net increase in LH and FSH at 30 minutes (delta LH and delta FSH) above the basal value. RESULTS delta LH and delta FSH showed a similar pattern of significant changes during the luteal-follicular transition. They decreased progressively from days -8 to 1 and increased on day 2. delta LH and delta FSH then decreased on days 3 and 4 and showed a further increase on days 5 and 7. In contrast to these changes, basal FSH levels increased from days -2 to 1 and remained high up to day 5, while basal LH levels showed a trend to increase only after the onset of menses. CONCLUSIONS These results demonstrate that the increase in basal FSH secretion during the luteal-follicular transition is GnRH independent. It is suggested that LH and FSH release under the stimulation by GnRH is regulated by a common mechanism.