OBJECTIVE Peripheral blood (PB) stem cell transplants are being increasingly used in the allogeneic setting, and are often preferred to the conventional bone marrow (BM) source. The aim of this report is to review available data on PB vs BM hematopoietic stem cell transplantation (HSCT). The discussion is restricted to unmanipulated HLA identical sibling transplants. METHODS Data with appropriate follow-up are available only for this type of comparison: we have preliminary data on the use of PB from unrelated donors, and on the use of T-cell depletion/CD34+ selection methods. The latter are rapidly evolving and it may be difficult to find a concurrent group of patients receiving T-cell depleted or CD34-selected marrow. BACKGROUND The results of retrospective and prospective studies are quite similar: hematologic and immune recovery is faster after PB grafts, acute graft-versus-host disease (GvHD) is comparable, whereas chronic GvHD is increased in recipients of PB transplants. Transplant-related mortality (TRM) is similar in the two groups, whereas disease recurrence is lower after PB grafts. CONCLUSIONS The general feeling is that PB grafts are indicated for patients with advanced disease, whereas for early phase patients the two sources may give comparable results.