Cytotoxic T lymphocytes (CTLs) are important effector cells of graft-versus-host disease (GVHD) and vascular endothelial cells are target cells of allospecific CTL. A combined assessment of T-cell activation and endothelial injury should result in a specific and sensitive test for GVHD. We examined circulating T lymphocytes for effector molecules involved in CTL-mediated endothelial injury. We analyzed CD4 and CD8 T lymphocytes of 24 long-term survivors of allogeneic stem cell transplantation with or without GVHD, and nine healthy, age-matched controls for signs of CTL activation and endothelial injury. IFN-gamma transcript levels in CD8 T cells were significantly elevated in SCT recipients with GVHD compared to patients without GVHD (767 CD3epsilon units/T cell (376-2050) vs 211 CD3epsilon units/T cell (159-274), P=0.01). Fas ligand transcript levels in CD4 T cells were significantly elevated in SCT recipients without GVHD compared to patients with GVHD (20 CD3epsilon units/T cell (0-78) vs 0 CD3epsilon units/T cell (0-0), P=0.01). Von Willebrand factor plasma levels were high in patients with GVHD, but normal in patients without GVHD (209 (186-254) vs 120 (100-141), P=0.0005). This assessment of T-cell activation and endothelial injury results in a sensitive and specific test to identify patients with active chronic GVHD.