Seven patients underwent treatment with mesenchymal stem cells (MSCs), together with allogeneic hematopoietic stem cell transplantation (HSCT). MSCs were given to three patients for graft failure and four patients were included in a pilot study. HSCT donors were three human leukocyte antigen (HLA)-identical siblings, three unrelated donors and one cord blood unit. The conditioning was myeloablative in four patients and reduced in three patients. MSC donors were HLA-identical siblings in three cases and haploidentical in four cases. Neutrophil counts >0.5 x 10(9)/l was reached at a median of 12 (range 10-28) days. Platelet counts >30 x 10(9)/l was achieved at a median of 12 (8-36) days. Acute graft-versus-host disease (GVHD) grade 0-I was seen in five patients. Two patients developed grade II, which in one patient evolved into chronic GVHD. One severe combined immunodeficiency (SCID) patient died of aspergillosis, the others are alive and well. One patient, diagnosed with aplastic anemia had graft failure after her first transplantation and severe Henoch-Schönlein Purpura (HSP). After retransplantation of MSCs and HSCs, she recovered from both the HSP and aplasia. Thus, co-transplantation of MSC resulted in fast engraftment of absolute neutrophil count (ANC) and platelets and 100% donor chimerism, even in three patients regrafted for graft failure/rejection.