To improve the safety of autotransplantation for myeloma, peripheral blood stem cell (PBSC) collection was attempted in 75 previously treated patients after the administration of high-dose cyclophosphamide (HD-CTX; 6 g/m2) with or without granulocyte-macrophage colony- stimulating factor (GM-CSF). Sixty patients subsequently received melphalan 200 mg/m2 (57 patients) or melphalan 140 mg/m2 and total body irradiation (850 cGy) (3 patients) supported by both autologous bone marrow and PBSC; 38 patients received GM-CSF posttransplantation. Among 72 patients undergoing PBSC apheresis, “good” mobilization (greater than 50 colony-forming units granulocyte-macrophage [CFU-GM] per 10(5) mononuclear cells) was achieved when prior chemotherapy did not exceed 1 year and when GM-CSF was used post-HD-CTX; similarly, rapid platelet recovery to 50,000/microL within 2 weeks was associated with “good” PBSC mobilization. These same variables also predicted for rapid engraftment after autotransplantation, so that hematologic recovery (granulocytes greater than 500/microL and platelets greater than 50,000/microL) proceeded within 2 weeks among the 37 patients with “good” PBSC collection. As a result of rapid neutrophil recovery (greater than 500/microL) within a median of 2 weeks, infectious complications both post-HD-CTX and posttransplant were readily manageable, resulting in only one treatment-related death post-HD-CTX. The cumulative response rate (greater than or equal to 75% cytoreduction) for all 75 patients was 68%, with 12-month event-free and overall survival projections of about 85%. Using both bone marrow and PBSC together with GM-CSF, autotransplants are safe and appear effective in myeloma, especially when prior therapy had been limited to less than 1 year. More than 80% of transplanted patients achieved complete hematologic recovery within a median of 1 month posttransplant (granulocytes greater than 1,500/microL; platelets greater than 100,000/microL; hemoglobin greater than 10 g%), thus providing sufficient hematopoietic reserve for further chemotherapy in the event of posttransplant relapse.