Pulsatile LH secretion was studied in six healthy postmenopausal women. Blood samples were obtained every 10 min during an 8-h saline infusion performed before and during the administration of transdermal oestradiol alone (E2; 50 micrograms/day) and in combination with vaginal progesterone (P; 100 mg twice daily). Plasma E2 and P levels reached values similar to those found in the early follicular phase and in the luteal phase of the menstrual cycle, respectively. The mean plasma LH levels significantly decreased (P less than 0.01) during transdermal E2 with and without vaginal P. A significant increase in the frequency (P less than 0.025) and the amplitude (P less than 0.05) of LH pulses was observed during transdermal E2. The administration of vaginal P to oestrongenized women significantly blunted the frequency (P less than 0.05) and enhanced the amplitude (P less than 0.05) of LH pulses. In all experimental conditions, the mean plasma LH levels showed a positive linear correlation with the amplitude of LH pulses. The present results show that peripheral levels of E2, similar to those of the early follicular phase of the menstrual cycle, can influence the pulsatile pattern of LH secretion, enhancing the frequency and the amplitude of LH pulses. In oestrogenized patients, the increase of peripheral P plasma levels to postovulatory values restored a pulsatile pattern of LH secretion similar to that of the early luteal phase of menstrual cycle.