Distinct syndromes are associated with a limited range of tumours. Autoantibodies are provoked by tumour (onconeural) antigens. Paraneoplastic antibodies to ion channels (VGCC, VGKC, AChR) are disease-inducing, but may also slow tumour growth in the case of LEMS. Antibodies to intracellular antigens in CNS disorders are probably not disease-inducing, but are valuable in diagnosis as disease markers. T cell mediated cytotoxicity is the likely effector mechanism in these latter disorders.