During the last few years, high-dose therapy with hemopoietic stem cell support has become a well-admitted therapeutic option for young patients with MM. The role of allogeneic or autologous graft and of blood rather than bone marrow as the source of hemopoietic stem cells must be further investigated. Autologous PBSC transplantation has, however, both practical and theoretic advantages over allogeneic and autologous BMT: (1) It can be applied to most patients, especially if blood stem cells are collected early in the course of therapy. (2) It usually induces relatively rapid hematologic reconstitution. (3) In comparison with autologous BMT, it appears to minimize the hazard of the reinfusion of malignant cells.