The functional capacity of the gonadotrophs was assessed by repeated stimulation with small doses of LH-RH (5 microgram intravenously at 2-hour intervals for 3 injections) in normal women during the early and late follicular phases of the menstrual cycle. The results were compared to those obtained when a single dose (100 microgram) of the neurohormone was administered. During the early follicular phase, the release of LH and FSH remained about equal after the 3 successive injections of the small and after the large dose of LH-RH. During the late follicular phase, the release of LH and fsh increased progressively after the repeated administration of the 5 microgram of the neurohormone while the large dose induced a more pronounced and a more sustained pituitary response. This hypersensitivity of the gonadotrophs is observed when the E2 concentrations are higher than in the early follicular phase of the menstrual cycle.