Myasthenia gravis (MG) and Lambert-Eaton myasthenic syndrome (LEMS) are autoimmune ion channel disorders mediated by antibodies to postsynaptic acetylcholine receptors and presynaptic voltage-operated calcium channels, respectively. MG and LEMS are currently treated with corticosteroids and immunosuppressive drugs with a positive clinical outcome. Since both diseases are mediated by circulating autoantibodies, they are good candidates for immunomodulation by intravenous immunoglobulins (IVIG). Standardized controlled studies are lacking in this field, but there is general agreement that IVIG are effective. They can be used as an acute treatment to control temporarily the most severe forms of these diseases, as well as a chronic immunomodulating therapy in addition to standard pharmacological treatment. Several aspects of IVIG administration, cost benefit-analysis, and comparison to plasmapheresis are still needed.