Three patients with POEMS syndrome were studied: two of them had myeloma, whereas the third had M protein without myeloma. Peripheral nerve biopsies showed no deposits of anti-Ig sera at direct immunopathological examination. Ultrastructural study revealed myelino-axonal degeneration in all three cases. This was associated in the first case with a dramatic loss of myelinated fibers and there were lesions consistent with acute degeneration in the second case. In addition, all three had some fibers showing uncompacted myelin lamellae. This peculiar modification has previously been reported only in cases of dysglobulinemia, lymphoma and inflammatory demyelinating polyneuropathy, but its mode of formation remains unclear.