Sensitization with GD1b has been shown to cause sensory neuropathy in rabbit. A patient with chronic sensory-dominant polyneuropathy who had IgM antibody specifically to GD1b has been reported previously. This report describes the first patient with acute demyelinating polyneuropathy with prominent sensory symptoms who had a high titer of serum IgG anti-GD1b antibody. The serum reacted with neither GM1 nor with other b-series gangliosides (GD2, GD3, GT1b and GQ1b). Improvement in symptoms was coincident with decrease in IgG anti-GD1b antibody titer after plasmapheresis. This case supports the experimental results in rabbit suggesting that anti-GD1b antibody functions in the development of sensory ataxia.