There has been a tremendous increase in interest in the neuropathogenicity of viruses during the past decade as we have come to recognize that the human immunodeficiency virus, which causes the acquired immunodeficiency syndrome (AIDS), can infect glial cells and cause neurological disease. Yet this increase has not been limited to AIDS but has extended to viruses that infect either or both the central and peripheral nervous systems. The changes examined here include both neurological and psychological diseases or syndromes. Moreover, the chapters in this volume review the interaction of the host immune system with the viruses examined and how such interactions may increase or decrease the neuropatho genicity of the viruses. Questions regarding viral neuropathogenesis include: (I) What is the mode of transmission of virus to the nervous system? (2) What types of cells are infected, and do they contain receptors for the virus? (3) What is the extent of damage that results from viral infection? (4) What are the immunologic mecha nisms by which damage is mediated or limited? Many of these questions remain unanswered, but this volume delves into efforts to provide some answers.