Amenorrheic runners (AR; N = 8), regularly menstruating runners (RMR; N = 9), and regularly menstruating sedentary controls (RMSC; N = 7) were compared for plasma progesterone levels, plasma lipid levels, menstrual cycle characteristics, physical characteristics, and nutritional adequacy to determine whether exercise training was the major factor associated with menstrual cycle disturbances. Plasma progesterone levels were significantly lower in the AR group subjects than those found during either the follicular or luteal phases of the menstrual cycle for either the RMR or the RMSC subjects. The RMR subjects had a shorter luteal phase length relative to their cycle length than did the RMSC subjects. The AR subjects consumed significantly less fat, red meat, and total calories than did the RMR subjects, while the RMSC subjects consumed significantly less total calories than did the RMR subjects. Serum LDL-C was significantly higher in the AR subjects when compared to that of the RMR subjects, while serum HDL-C was significantly higher for both the AR and RMR subjects when compared to that obtained for the RMSC subjects. The nutritional inadequacy would appear to separate the AR from the RMR, and, thus, the exercise training performed by the athletes at the time of the present investigation alone does not appear to be the major factor associated with athletic amenorrhea.