We encountered two patients with uncommon neurological manifestations after allogeneic bone marrow transplantation (BMT), which occurred with rapid elevation of the leukocyte count at engraftment. Both patients then developed severe acute graft-versus-host disease (GVHD). To investigate the pathogenesis, we measured the levels of soluble P-selectin, von Willebrand factor (vWF) and thrombomodulin (TM), which reflect endothelial damage. The P-selectin, vWF and TM levels in the patients with (n=2) and without (n=5) neurotoxicity were, respectively, 168.5+/-52.5 ng/ml vs 27.7+/-3.9 ng/ml, 6.7+/-0.15 FU/ml vs 3.42+/-0.41 FU/ml and 459+/-37% vs 189.4+/-32.4% (mean+/-s.d.). All three parameters were much higher in the patients with neurological complications. These results suggest that neurotoxicity after BMT may be related to endothelial damage.