Currently available as a dietary supplement, the pineal hormone melatonln is portrayed by the media as a formidable weapon against disease and aging. Accordingly, primary health care providers should be cognizant of which of its proposed uses are supported by biomedical research and which are, as yet, un-proven. Melatonin entrains circadlan rhythms and, thus, can treat jet lag, delayed sleep phase syndrome, and sleep disorders in the blind and in some neurologically Impaired children. By virtue of its hypnotic effect, melatonin can mitigate Insomnia in the elderly. Reductions In melatonin secretion have been associated with many disorders, including cardiovascular disease, Alzheimer's, diabetes, SIDS, and aging; however, melatonln's role in their etiology and/or pathophysiology is unproven. Preliminary studies suggest a possible adjuvant therapeutic role for melatonin In cancer therapy. Melatonin secretion is reduced by alcohol, caffeine, and some commonly prescribed drugs. Since tolerance, fatigue, and other side effects have been reported, melatonin use on consecutive nights should be avoided and only the lowest effective hypnotic dose should be taken.