To clarify a controversy as to whether melatonin secretion is related to body weight, urinary sulphatoxymelatonin (aMT6s) excretion was estimated in 10 patients with anorexia nervosa before and after weight gain, and compared with 10 age-matched controls. There was no change in aMT6s excretion after weight gain, and no significant difference between the patients and control groups at either point. Significant increases in plasma LH, FSH, and estradiol were detected after weight gain in anorexic patients, independent of aMT6s excretion.