Patients with paraneoplastic neurological disorders (PNDs) provide a unique model for studying tumor immunity and neuronal autoimmunity. We hypothesize that T lymphocyte autoimmune dysfunction is involved in the pathogenesis of the paraneoplastic neurological syndromes, and that killer T cells are involved in the targeting and successful killing of tumor cells in these cancer patients. Furthermore, we postulate that this activity may provide a model for autoimmune brain disease. We will assess the immune responses in PND patients, correlate these with the clinical data (time course of disease, symptoms and signs, disability), and collect and archive clinical data, serum and cells from PND patients for current and future studies into the basic immune system phenomenon present in PND patients.