Five cases of histologically verified plasma cell myeloma in sclerotic skeletal foci and polyneuropathy are reported. Thirty similar cases were collected from the literature. They illustrate a special form of plasma cell neoplasia. The characteristic features are osteosclerosis, polyneuropathy resembling polyradiculitis, approximately normal hemoglobin concentration, bone marrow smears and ESR, low concentration of M-protein, and absence of Bence-Jones' proteinuria. Slow progesssion of the disease is a possible additional feature. It is hypothesized that autoimmune mechanisms are involved in the pathogenesis. This hypothesis is based on the observation of circulating immune complexes, positive Waaler's reaction and relative increase in the number of circulating B-lymphocytes.