Background: Several studies suggest that leptin modulates the reproductive axis function. Leptin may stimulate release of GnRH from hypothalamus and of gonadotrophins from the pituitary. A synchronicity of LH and leptin pulses has been described in healthy women and in patients with polycystic ovarian syndrome (PCOS), suggesting a relationship between the episodic secretion of LH and leptin. In vitro experimental studies have demonstrated that leptin administration promotes GnRH-LH release. However it is not established whether GnRH promotes the episodic secretion of leptin. Aim: To assess the response of LH and leptin to the administration of a GnRH bolus in hyperandrogenic and healthy women. Patients and methods: Eleven hyperandrogenic and eleven healthy women of similar age and body mass index (BMI) were studied. Under basal conditions three blood samples were collected every 30 min before and after the administration of a GnRH bolus (100 µg). LH and leptin concentrations were measured in all samples. Testosterone, SHBG and estradiol were determined in the first sample. For data analysis, the increment of LH and leptin between 0-30 and 0-60 min. was calculated. The LH and leptin areas under the curve (AUC) before and after GnRH administration were also calculated in both groups. Results: After GnRH administration. an increment in LH concentrations was observed in both groups; however, leptin concentrations were not modified. In both groups LH area under the curve increased after GnRH administration; however, the leptin area was not modified. Conclusions: These results suggest that circulating leptin concentration is not modulated by GnRH-LH. (Rev Méd Chile 2000; 128: 460-6)