A 56-year-old man complained of general malaise, diffuse bone pain, nocturnal sweating, lack of appetite and weight loss (7 kg within one year). Pain in the pelvic and lumbar regions markedly impaired movement. Roentgenologically, multiple lucencies were visualised in many skeletal areas. Examination of the bone marrow revealed an increase in the proportion of atypical plasma cells to 40%. The IgG concentration was 29.8 milligrams, mainly monoclonal immunoglobulins of the IgG-kappa type, which reacted against nuclear antigens (68-kD-U1-RNP nuclear protein) with a 1:2,000 titre. The symptoms markedly regressed under cyclical combined therapy with three times 5 mg melphalan daily for 4 days and 100 mg prednisolone daily for 7 days (a total of 24 cycles). At the same time the IgG concentration and the autoantibody titre decreased markedly and the patient became symptom-free.