['To investigate the effect of exogenous melatonin on LH pulsatility in women during the follicular and luteal menstrual phases.', 'Randomized, double-blind placebo-controlled study.', 'Normal cycling young women (25 to 35 years old).', 'Each subject was admitted at the Clinical Research Center for 2 consecutive days on both the follicular and the luteal menstrual phases. On each day, at 7:00 A.M. an indwelling catether was placed in an antecubital vein for a 10 minutes blood sampling from 9:00 A.M. to 5:00 P.M. On the 2 consecutive days of both the follicular and the luteal menstrual phases, each subject randomly received either placebo or melatonin pills (1 mg at 8:00 and 0.75 mg at 10:00 and 12:00 A.M.).', 'Luteinizing hormone pulsatility.', 'The amplitude of LH pulses and mean LH levels were increased by melatonin in the follicular but not in the luteal menstrual phase.'] Does exogenous melatonin enhance luteinizing hormone levels of women in the follicular but not in the luteal menstrual phase?