Three Kallmann syndrome (KS) patients were examined to assess characteristics of LH response to GnRH bolus, with and without GnRH sensitization using Instantaneous Secretory Rate (ISR) computation before and after estriol treatment (60 days, 2 mg/day). Six healthy women were enrolled as controls and underwent GnRH bolus during the early follicular phase (days 3-5 of the menstrual cycle). After estriol treatment, the KS patients showed a higher LH response to GnRH bolus and similar LH pulse duration to healthy controls. These data support the hypothesis that the administration of weak estrogen improves LH response to GnRH in hypogonadotropic women with KS.