Severe GVHD is a lethal complication to ASCT, and a number of approaches are therefore being evaluated. Recently, Le Blanc et al. reported a case of grade IV therapy-resistant acute GVHD of the gut and liver that showed rapid improvement after infusion of mesenchymal stem cells. Here we describe two pediatric patients who developed severe refractory acute GVHD following ASCT and were successfully treated with AMSC from HLA-mismatched unrelated donors.