Median survival in patients with multiple myeloma, which amounted to 6-12 months during the pre-chemotherapy era, was improved to 28-43 months following the introduction of chemotherapy. Usually patients with stage II or III myeloma require treatment. Conventional chemotherapy with melphalan-prednisone is undertaken if their prognosis is good; in case of poor prognosis and good general condition, a more aggressive polychemotherapy is given. High-dose melphalan therapy alone induces high remission rates, but fails to prolong remission duration or survival. Resistance to cytostatic drugs due to the p-glycoprotein coded by the MDR-gene is treated by a combination of cyclosporin-A or verapamil and VAD. For the treatment of relapses or of primarily resistant patients several second-line regimens are available. As remission maintenance therapy, interferon has so far yielded the best results. Trials of other cytokines such as interleukin-2 and interleukin-4 are still inconclusive. For autologous bone marrow transplantation, primary reduction of the tumour mass by conventional polychemotherapy is recommended. Subsequently, high-dose melphalan or cyclophosphamide-busulfan--with or without total body irradiation--is used for conditioning and followed by the transplantation of either autologous bone marrow or peripheral blood stem cells. Significantly higher remission rates and longer survival of the patients may be expected. Allogenous bone marrow transplantation is burdened with a high early mortality rate, but it also promises longer disease-free survival times. Bone marrow transplantation should be performed as early as possible in the course of the disease. More controlled studies are required before a definite evaluation of its efficacy is possible.