In four cases it was the existence of peripheral neuropathy which led to the discovery of macroglobulinemia within an interval from 1 to 11 years. The treatment of the disease also markedly improved the peripheral neuropathy in three cases. Two patients died. Two of the biopsies of the peripheral nerve showed infiltration by atypical lymphocytes. Ultrastructural changes in the five cases were variable. Marked axonal involvement in the two cases with cellular infiltration. In one of these two cases it was combined with segmental demyelinization. This lesion was clearly predominant in the three other cases. In one of them demyelinization occurred in a very peculiar way with dilation of the internal part of the mesaxone going on in the most peripheral layers of the myelin. Discussion of the mechanisms of the involvement of the peripheral nervous parenchyma in Waldenström's disease. Cellular infiltrations, amorphous deposits, changes in the capillaries and macroglobuline may occur.