The immune, endocrine and nervous systems communicate with each other through a network of molecules which collectively produce a coordinated response to immune challenges. This phenomenon, necessary for the survival of the organism, is thought to involve cytokine release by activated immune cells, the secretion of several hormones by specific glands, and the release of particular neurotransmitters from autonomic nerve endings in the immune system. Readers of this publication will find reviews on several mechanisms involved in mutual communication among immune, endocrine and nervous systems on the basis of physiological, cellular and molecular data. It provides valuable information on how cytokines affect adenohypophysial hormone release and animal's behavior and to what extent they modify the circadian release of a number of hormones. Contributions also include an analysis of the role of sympathetic nerves in modulating immune responses in lymph nodes and of the regulatory role of melatonin in communication between the neuroendocrine and the immune systems. This state-of-the-art summary will be of most benefit basic and clinical neuroscientists interested in neuroimmunology.