Percentage body fat is predictive of the onset of menstruation at puberty. In anorexia nervosa a relationship between luteinizing hormone (LH) levels and percentage weight loss has been reported. In the current study the relationship of percentage body fat and of percentage weight loss to LH and LH reactivity was examined in anorexia nervosa. Fifteen women with anorexia nervosa were studied. The resting levels of LH were measured, and in seven of the subjects LH response to luteinizing hormone releasing hormone (LHRH) and clomiphene was tested. The increment in plasma LH was measured in response to a 100 microgram dose of LHRH, and also to a 5-day course of clomiphene 100 mg. The resting LH levels were found to correlate with percentage fat, body weight, and percentage weight loss. Correlations were also found between the response to either LHRH or clomiphene and percentage weight loss, percentage fat, and absolute body weight. Other pituitary hormones measured did not show a relationship to body fat or weight. It is concluded that in addition to being predictive of the onset of menstruation, percentage body fat is significantly related to resting LH and LH reactivity in anorexia nervosa. Although percentage body fat, percentage weight loss, and absolute body weight are all significant correlates of LH reactivity, we cannot at this time conclude that any one in particular is the superior.