High dose intravenous immunoglobulin (IVIg) is an effective treatment for demyelinating neuropathies. IVIg was given to five patients with multifocal motor neuropathy, a motor neuropathy showing a clinical syndrome of asymmetrical weakness and amyotrophy, electrophysiological evidence of motor conduction block and, in many cases, high titres of serum anti-GM1 antibodies. Muscle strength was evaluated by a conventional score before and after each IVIg course. In all patients there was relevant improvement on muscle strength after each immunoglobulin course, but in most cases the clinical benefits partially declined after three to eight weeks. At the eight month follow up, however, the pretreatment examination showed a significant improvement compared with the initial evaluation. The effects of each IVIg course were still present after a number of courses. Electrophysiological study revealed a decrease in conduction block in one or more nerves in all patients. However, conduction block was unchanged or increased in other sites. IVIg treatment did not affect anti-GM1 antibody titres.