This article has been designed to review recent development in the field of hypothalamic natural and synthetic LH/FSH-releasing hormone on the following problems: 1) Historical development (demonstration of the existence of LH/FSH-RH, its isolation and purification.) 2) Methods of measurement. 3) Chemical structure (decapeptide), its analogues and functions. 4) Modes of action. a) Mechanism of action. b) Release of synthesis of gonadotropin. c) Regulatory mechanism of sexual function by hypothalamus. 5) Clinical studies with synthetic LH/FSH-RH. a) Induction of ovulation. b) Function test of hypothalamic-pituitary-gonadal system.