The feedback loops involved in the neural control of reproductive cyclicity in primates are reviewed. A combination of morphological, endocrinological, and surgical experimental approaches was used to identify the different mechanisms involved. The main signal for pituitary secretion of gonadotropins is the estrogen secreted by the ovary. Estrogen probably affects the hypothalamic secretion of gonadotropin-releasing hormone (GnRH), which in turn stimulates the pituitary production of gonadotropins. These may in turn, through a short feedback loop, regulate the secretion of GnRH. Evidence for a direct effect of estrogen on the pituitary is presented. Future possible areas of research, including extrahypothalamic influences on reproductive mechanisms, are briefly outlined.