To investigate endothelial cell alterations in BMT recipients developing acute graft-versus-host disease (aGVHD) we determined levels of the endothelial cell markers von Willebrand factor (VWF) and thrombomodulin (TM) in 57 patients undergoing BMT. Before conditioning VWF and TM levels did not differ significantly between transplant recipients who later developed no or mild (grade I) aGVHD (group A, allogeneic n = 22, autologous n = 7; VWF 136.0 +/- 44.1%; TM 29.5 +/- 18.0 ng/ml), and those with moderate or severe (grade II or III) aGVHD (group B, n = 28; VWF 142.2 +/- 37.6%; TM 35.2 +/- 20.1 ng/ml). A first significant rise of both VWF and TM level was noted after conditioning (day 0) both in group A (VWF 197.0 +/- 113.3%; P < 0.001; TM 39.3 +/- 23.3 ng/ml; P < 0.01) as well as in group B (VWF 201.7 +/- 53.3%; P < 0.0001; TM 43.5 +/- 23.5 ng/ml; P < 0.05). Subgroup analysis of autografted patients revealed no significant increase after conditioning in these patients. At the time of engraftment and onset of aGVHD (day 21), when VWF and TM levels within the groups were significantly elevated as compared with baseline (day -8) levels, group B patients (62.7 +/- 38.5 ng/ml) had significantly higher (P < 0.01) TM levels than patients of group A (37.4 +/- 19.6 ng/ml). This significant elevation also persisted at the end of the investigational period (day 28; group B: 56.0 +/- 37.6 ng/ml; group A: 38.2 +/- 23.7 ng/ml; P < 0.01). An elevation of endothelial cell markers is found in the course of BMT, particularly after conditioning and at the time of engraftment. This increase is pronounced in patients with aGVHD suggesting not only epithelial cell but also endothelial cell injury during aGVHD.