This article has been designed to review recent developments in the field of hypothalamic hormones involved in the control of reproductive functions. A brief resume of early physiologic and anatomic studies was presented initially to give a better understanding of the concept of hypothalamic regulation of the release of gonadotropic hormones from the pituitary gland. Recently, an advance was achieved with the isolation from porcine hypothalami of a decapeptide which has both FSH-releasing hormone (FSH-RH) activity and LH-releasing hormone (LH-RH) activity. Its amino acid sequence was determined to be (pyro) gluhis-trp-ser-tyr-gly-leu-arg-pro-gly-NH2. The decapeptide corresponding to this structure was synthesized and shown to stimulate the release of LH and of FSH in laboratory and domestic animals and human beings. Natural and synthetic FSH-RH/LH-RH also stimulated the synthesis of both gonadotropins in tissue cultures of rat pituitaries in vitro. It was postulated that this decapeptide represents the hypothalamic hormone which regulates the release of both LH and FSH from the anterior pituitary gland. Complex effects of sex steroids on the release of LH and FSH were reviewed briefly. It was suggested that the over-all control of secretion of FSH and LH is most likely mediated by the interaction of hypothalamic FSH- and LH-releasing hormone with sex steroids. Clinical studies performed with natural and synthetic LH-RH/FSH-RH were reviewed. These studies, particularly induction of ovulation, suggest that LH-RH should find practical application in the treatment of sterility. Subsequent synthesis of LH-RH/FSH-RH by several laboratories and drug houses should provide enough material for large-scale clinical evaluation of this hormone. Some comments were made concerning probable clinical use of LH-RH. Finally, some speculations were offered about the possibility of developing new birth control methods based on LH-RH/FSH-RH, its analogues, or its derivatives.