The central nervous system (CNS) and the immune system, communicating through the neuroendocrine system, are closely involved in the individual's adaptation to the environment. The data from basic science research and clinical observations are overviewed, and more recent studies are summarized. As changes in immune function may mediate the effects of psychosocial factors in psychosomatic disorders, it is important for all biopsychosocially oriented physicians to understand the network that connects the central nervous and immune systems.