Autoreactive T cells are a component of the normal immune system. It has been proposed that some of these autoreactive T cells even have a protective function. Recent studies support this notion by demonstrating that (a) myelin basic-protein (MBP-) specific T cells show neuroprotective effects in vivo, and (b) activated antigen-specific human T cells and other immune cells produce bioactive brain-derived neurotrophic factor (BDNF) in vitro. Furthermore, BDNF is expressed in different types of inflammatory cells in brain lesions of patients with acute disseminated leukoencephalopathy or multiple sclerosis. We postulate that the neuroprotective effect of T cells and other immune cells observed in vivo is at least partially mediated by BDNF and other neurotrophic factors. The concept of neuroprotective autoimmunity has obvious implications for the therapy of multiple sclerosis and other neuroimmunological diseases.