['To determine whether the opioidergic system is involved in the modulation of leptin secretion in healthy and amenorrheic subjects.', 'Prospective study.', 'Department of Obstetrics and Gynecology, University of Modena, Modena, Italy.', 'Healthy subjects (n = 8) and patients with hypothalamic amenorrhea (n = 17) or hyperandrogenism (n = 7) and low body mass index (BMI).', 'Acute infusion of naloxone (4-mg bolus) and blood sampling 15 minutes before infusion; at time of infusion; and 15, 30, 45, 60, 75, 90, and 120 minutes after infusion.', 'Plasma leptin, LH, FSH, E2, and cortisol concentrations.', 'Plasma leptin concentrations were lower (P <.01) in both hypothalamic and hyperandrogenic amenorrheic subjects than in healthy controls. In all groups of subjects, no significant changes in leptin levels were observed after infusion of naloxone. A significant correlation was found between leptin concentrations and BMI when all subjects were considered together (P <.05) but was not found in the single groups.'] Does acute infusion of naloxone , an opioid receptor antagonist , modify serum leptin concentrations in amenorrheic and healthy women?