There is increasing evidence of reciprocal CNS-immune system interactions. The reaction of such processes to behavior and psychiatric disorders remains to be determined. It is not clear at this time if alterations in measures of the immune system associated with stress have clinical relevance, nor is there evidence that immune alterations are associated with the pathogenesis of psychiatric disorders. With the exciting advances in neurobiology, immunobiology, and biologic psychiatry, and with the availability of a wide range of methodologies, elucidation of the complexities of brain, behavior, and the immune system may be achieved.