Intense physical exercise has been associated with reproductive dysfunction and menstrual cycles may be abnormal in a majority of women with a heavy training load. To determine whether training influenced pulsatile LH release, we measured LH pulse frequency, LH pulse amplitude and area under the curve over six hours during the early follicular phase of the menstrual cycle in four sedentary women and six eumenorrheic women runners with a training volume of at least 32 km per week. All three LH variables were significantly lower in runners than in controls. These data suggest that there is a central inhibition of the hypothalamic-pituitary-gonadal axis in eumenorrheic runners.