The results of the initial studies using GnRH in the treatment of HH were actually poor. Back in 1977, Krabbe [2] et al. attempted GnRH treatment in two boys with Kallmann syndrome. After 4 weeks of treatment with subcutaneous GnRH 200 mg given every 8 hours, although the patients’ serum FSH rose to normal adult male levels, luteinizing hormone (LH) and testosterone levels remained essentially unchanged before and after treatment, and no clinical signs of pubertal development initiation appeared. Similar treatment trials during the same period were unsuccessful [3]. A year later, the mechanism of action of the pulsatile secretion pattern of GnRH for gonadotropic cells was elucidated by Jin Nan, Department of Endocrinology, 301 Hospital, Beijing. The investigators found that in rhesus monkeys with hypothalamic damage resulting in deficiency of pituitary gonadotropin secretion, continuous administration of exogenous GnRH did not restore pituitary gonadotropin secretion. In contrast, gonadotropin secretion was restored to normal when the treatment was changed to pulsed administration every 1 hour [4]. Since then, domestic and foreign scholars have successively confirmed that the same abnormalities in the frequency and amplitude of GnRH and LH pulses exist in patients with IHH [5, 6]. As a result, investigators have changed the strategy of GnRH therapy. Several studies confirmed significant efficacy in testicular enlargement and spermatogenesis when GnRH was changed to pulsatile administration [7, 8].In 1982, Hoffman et al. first treated six male patients with IHH using a GnRH pulsatile pump [9]. All patients showed significant increases in LH and testosterone levels and spontaneous erections after treatment, and sperm were detected in the semen of three patients at 43 weeks of treatment. In China, Zhang Guiyuan et al. first applied pulsed GnRH to treat four patients with IHH with success [10]. four male patients with IHH, after receiving pulsed GnRH at 5ug given subcutaneously every 90 minutes, all showed significant improvement in secondary sexual characteristics, increased testicular volume, two of which reached the level of normal adult men, and mature spermatozoa at days 250 and 330 of treatment. In 2004, Henriette et al. observed 68 patients with HH including IHH, Kallmann syndrome and postoperative intracranial tumors [11]. Treatment was performed by intravenous or subcutaneous administration of 2-20ug pulses of GnRH every 90 min. All 68 patients had elevated LH, FSH and testosterone levels, and all showed secondary sex development and testicular enlargement. The mean testicular volumes of the patients increased from 4.2, 2.6 and 4.3 ml before treatment to 14.2, 10.6 and 18.2 ml, respectively; 56 of them had total serum testosterone levels above 10 nmol/L, reaching normal adult male levels. Spermatogenesis was seen in 58.