Urinary luteinizing hormone (LH) and the melatonin metabolite (6-sulfatoxymelatonin; aMT6s) were measured in normal young men following early morning light exposure. Eleven young healthy men ages 19-30 years participated in this study. During separate weeks in counterbalanced order, each subject received both 5 days of bright light treatment (BL) and 5 days of placebo light treatment (PL) for 1 h (05:00-06:00). LH excretion was increased 69.5% after bright light exposure, but was not changed by placebo light exposure. The acrophases and offsets of aMT6s were advanced, but the duration of aMT6s excretion was not changed after BL. Light stimulation of LH could have interesting applications in psychiatry and reproductive endocrinology.