MSC have been suggested to be the precursor cells in the bone marrow stroma that provide a scaffold and promote hematopoiesis. They have therefore been suggested to enhance engraftment after autologous and allogeneic HSC transplantation. In patients undergoing transplantation, MSC infusion was shown to be safe and to enhance engraftment of HSC, as well as to reduce the incidence of both acute and chronic GVHD. We cotransplanted haploidentical AMSC with HLA-identical sibling-matched PBSC in two pediatric patients with refractory SAA after primary or secondary graft failure. At present, the two patients are more than two yr after cotransplantation without any treatment, transfusion-independent and in good condition. Thus, cotransplantation of MSC might enhance engraftment of HSC in patients regrafted for graft failure.