Monoclonal gammopathies are frequently associated with peripheral neuropathies of which clinical, electrophysiological, pathological and possibly pathogenetical aspects are heterogeneous. Nevertheless some clinico-biological entities, which account for the majority of cases, have been recently recognized: 1) The IgM neuropathy is a chronic demyelinating sensori-motor polyneuropathy with tremor and ataxia as prominent features. It can be either associated with MGUS or Waldenstrom macroglobulinemia. The light chain of the gammopathy is kappa in a majority of cases. Numerous reports have demonstrated specific antibody activities supported by the M-protein and directed against various peripheral nerve antigens, usually myelin components such as the myelin associated glycoprotein (MAG). The ultrastructural evidence of widely spaced myelin is suggestive of the diagnosis but is not consistent. Treatment directed towards the gammopathy is occasionally associated with improvement of the symptoms. 2) The neuropathy of the osteosclerotic myelomas and solitary plasmacytomas present as a chronic sensori-motor polyradiculoneuropathy with conspicuous demyelination and may be associated with one or more of the systemic clinical features of the Crow-Fukase or POEMS syndrome (Polyneuropathy, Organomegaly, Endocrinopathy, M-protein, Skin changes). The POEMS syndrome may also be associated with "benign" monoclonal or even polyclonal dysproteinemias. The M-proteins are almost all IgG or IgA with lambda light chains. There are some relations between POEMS syndrome and Castleman's disease. The pathogenesis of both disorders remains obscure. Treatment is most favorable in case of solitary plasmacytomas, which may be completely removed. 3) The neuropathy observed in patients with primary AL amyloidosis or amylosis associated with malignant plasma-cell dyscrasias is rare. Sensory deficit and autonomic dysfunction are related to a prominent involvement of small myelinated and unmyelinated fibers. A clinical and/or electro-physiological carpal tunnel syndrome is frequent. In a majority of cases the light chain of the M-protein is lambda. Amyloid deposits are observed on nerve biopsy. Treatment is inefficient. 4) The neuropathy associated with cryoglobulinemias may be asymmetric, painful, cryosensitive and associated with cutaneous purpura and neuromuscular vasculitis. In fact, in a majority of cases the symptoms are less suggestive raising the problem of an incidental laboratory finding. 5) A motoneuron disease-like syndrome may develop in patients with various types of monoclonal gammopathies.(ABSTRACT TRUNCATED AT 400 WORDS)