Current treatment in multiple myeloma consists of three courses of chemotherapy in low doses with subsequent hematopoietic stem cell mobilization to the peripheral blood using high-dose cyclophosphamide, collection and conditioning with high-dose chemotherapy (melphalan) followed by retransplantation of autologous peripheral blood stem cells (PBSCT). Only a few studies compare the effects of different phases of therapy on parameters, such as monoclonal immunoglobulin level and the presence of malignant CD38(+) and CD56(+) cells in blood and marrow. The aim of this study was to compare the effects of these two major phases of treatment (conventional and high dose) in the same patients, and furthermore, to compare the effects of the second course of high-dose therapy followed by PBSCT with the effects of the first one. Fifteen patients were included in the study. On average, conventional chemotherapy only slightly reduced the values of all disease markers. In contrast, high-dose therapy resulted in a dramatic effect, rapidly normalizing the values of all parameters. The effects of second PBSCT were only modest compared to the first. These data suggest that high-dose therapy is an efficient method to reduce tumor load in multiple myeloma. Conventional-dose chemotherapy may be simply a waste of time for some patients and may be either omitted or administered after high-dose therapy to consolidate remission.