The clinical applications of immunology in neurology are reviewed in relation to autoimmunity, immunosuppression, brain tumour immunity and the transplantation of peripheral nervous tissue. Evidence for considering the role of immunological factors in certain neurological diseases is considered. The clinical value of immunosuppressive therapy in these diseases is discussed. Attention is drawn to immunotherapy as a possible adjunct to present methods of treating gliomas. Finally, possible uses of transplants of peripheral nerve and muscle are mentioned.