Allogeneic stem cell transplantation (allo-SCT) is the only curative option for many patients with hematological malignancies. It is therefore crucial that allo-SCT is utilized appropriately to optimize efficacy and limit toxicity. Here, Thomas Luft, MD, PhD, from Heidelberg University, Heidelberg, Germany, identifies the key contributor in graft-versus-host disease (GvHD), the most significant complication present in patients who have undergone allo-SCT. Speaking from the 2018 European Society for Blood and Marrow Transplantation (EBMT) Annual Meeting in Lisbon, Portugal, Dr Luft discusses the endothelial cell marker angiopoietin-2 and the single nucleotide polymorphisms in the thrombomodulin gene, which may be used to identify the risk of GvHD occurring in patients undergoing allo-SCT.