Over the past decade, the potential of the pineal hormone melatonin as a therapeutic agent in a variety of diseases has been recognized. This book is the first to review the effect of melatonin in sleep disorders, its possible use as an immunoregulatory agent and clinical results obtained in cancer immunotherapy. Several papers are devoted to the pharmacological and molecular characterization of melatonin receptors in a variety of cell types. Other contributions further investigate the immunoenhancing effect of melatonin, such as in viral encephalitis and bacterial infections, and consider possible therapeutic indications. Melatonin is also reported to exert important hematopoietic effects by stimulating the production of novel T helper cell opioid cytokines. Other basic studies introduce new perspectives describing melatonin as a potent free radical scavenger. This book should be read by clinicians working in the fields of sleep disorders, oncology and infectious diseases as well as by scientists active in the field of neuroimmunomodulation. It will also be very useful to all those interested in melatonin as a therapeutic agent.