Fezolinetant (ESN364, 1 mg/kg, iv bolus) reversibly inhibits the regular, pulsatile secretion of LH in the ovarectomized ewe. ESN364 represses the pulse pattern of LH in all treated animals. ESN364 (5 mg/kg, p.o.) lowers plasma LH, but not FSH, in the castrated monkey. ESN364 (10, 25, 50 mg/kg, orally) also blocks the LH surge and decreases ovarian hormone levels throughout the menstrual cycle in monkeys.