This volume brings together reviews of the areas of clinical medicine where the pineal gland hormone melatonin is thought to play an important role. The contributors discuss the possible role of melatonin in the occurrence of schizophrenia, its effects on human reproductive function, the circadian system, thyroid function, and sleep, and the pharmacology of melatonin and antidepressant drugs. This timely work provides the first synthesis of basic and clinical research in an area of growing interest for clinicians and investigators in endocrinology, biochemistry, and physiology.