In this review of the role of the hypothalamus as a regulator of reproductive function we have presented a short history of the important anatomical and physiological findings, the structure and properties of gonadotrophin releasing hormone and its function and mode of action in the reproductive process. The latest clinical studies have been presented and we have discussed the therapeutic and diagnostic applications of GnRH. Although the progress in the last few years has been relatively enormous, research on the physiological and clinical implications of these discoveries has probably only now reached its peak and it was thus felt that the time was ripe to write this summary.