Patient 1 was a 39-year-old man; patient 2, a 42-year-old woman; patient 3, a 78-year-old man. Leading symptoms were chronic asymmetrical weakness in all three cases, which started in a distal portion of the upper extremities. Muscle atrophy was often less prominent than would be expected from the power of the muscle. Fasciculations were observed in two patients and the initial symptom of patient 2 was painful cramp of the right thumb. Patient 1 initially had mild transient dysesthesia of the right fingers. The other two patients had no sensory symptoms or signs. General laboratory tests revealed no particular abnormalities except that patient 3 had mild diabetes mellitus, although the type of neuropathy in patient 3 was quite different from diabetic neuropathy. Total protein concentrations in the cerebrospinal fluid were 34, 32 and 43 mg/dl in three patients, respectively (normally, less than 40 mg/dl). Motor nerve conduction studies revealed conduction block in more than one nerve in every case. Conduction velocities were generally normal in those segments of nerve where conduction block was not detected. Serum anti-ganglioside antibodies were investigated by Enzyme-linked immunosorbent assay (ELISA). Glycolipids used as the antigen include GM1, GM2, GM3, GD1b, GD3, GT1b, GQ1b, GA1 and galactocerebroside. Strong IgM antibody activity against GM1, GD1b and GA1 was noted in patient 1. Weaker but significant IgM antibody activities against GM1 and GA1 were detected in patient 2 and 3. Thin-layer chromatography immunostaining also confirmed these results. Muscle biopsy in patient 1 revealed a lot of target fibers and profuse polyglucosan bodies in the axons of intramuscular nerves.(ABSTRACT TRUNCATED AT 250 WORDS)