Bilateral implantation of small amounts of progesterone in the amygdala, cerebellum, and median eminence of castrated female rats results in an increase of pituitary stores of LH and in a decrease of hypothalamic stores of LH-RF. Similar implants placed subcutaneously or in the cerebral cortex are ineffective. It is suggested that the amygdala and the cerebellum contain receptors sensitive to progesterone and intervene in modulating the negative, inhibitory effect that this steroid exerts onLH secretion.