High-dose cyclophosphamide (HD-CY) has been shown to decrease the tumor mass in multiple myeloma (MM) patients and to be effective in the mobilization of PBPC. By administering hematopoietic growth factor the quantity of progenitor cells in the peripheral blood increased and the hematological toxicity of CY could be reduced. Thirty-two patients with stage II and stage III MM were treated to mobilize and harvest a sufficient amount of PBPC for autologous transplantation. Sixteen patients received 4 g/m2 CY and 16 patients 7 g/m2 CY in divided doses of 1 g/m2 every 2 h. Both patient groups were comparable for disease stages as well as previous therapies. Twenty-four hours after chemotherapy 300 micrograms GCSF were administered subcutaneously once daily until the last day of leukapheresis. Administration of 7 g/m2 HD-CY resulted in statistically significantly higher peak values for CD34+ progenitor cells (47.86/microliters vs 18.75/microliters, P = 0.0198) in the peripheral blood. PBPC autografts containing > 2.5 x 10(6) CD34+ cells/kg BW could be obtained at the first attempt from 14 of 16 patients treated with 7 g/m2 CY as compared to 10 of 16 patients treated with 4 g/m2 CY (P = 0.11). The analysis of potentially malignant CD19+ B cells showed a highly significant lower mean CD19+ cell content/kg BW per leukapheresis in the 7 g/m2 compared to the 4 g/m2 CY group (0.75 vs 1.81 x 10(6), P = 0.001). WHO grade IV treatment-related non-hematologic toxicity was not observed. We prefer the 7 g/m2 CY dosage followed by cytokine administration for the mobilization of PBPC in advanced state MM patients pretreated with alkylating agents.