BACKGROUND: Toxic epidermal necrolysis (TEN) and Stevens-Johnson syndrome (SJS) are characterized by extensive keratinocyte apoptosis mediated by cytotoxic proteins. Similar features have been found in another severe dysimmune syndrome, allogeneic acute graft-versus-host disease, where endothelial cell apoptosis has been recently characterized. OBJECTIVES: To determine whether endothelial cell apoptosis occurs in dermal vessels of TEN and SJS, and whether it is linked to expression of cytotoxic proteins. METHODS: Skin biopsies of eight patients with severe drug-induced bullous eruptions (four TEN, four SJS), eight with drug-induced urticaria and eight healthy controls were compared. Blood vessel damage was studied by electron microscopy and quantified by CD31 immunostaining. Apoptotic cells, characterized by electron microscopy, were quantified on terminal deoxyribonucleotidyl transferase-mediated deoxyuridine triphosphate nick end labelling assay. Immunohistochemistry was also used to characterize and quantify inflammatory cells and granzyme B, tumour necrosis factor (TNF)-alpha and Fas ligand (FasL) expression. RESULTS: Endothelial cell apoptosis was observed in all TEN and SJS cases: it occurred in 85% of the vessel sections. It occurred in one case of drug-induced urticaria, in 5% of vessel sections, but not in healthy controls. Numbers of CD68+ macrophages and CD8+ T lymphocytes were significantly higher in TEN and SJS compared with both other groups; granzyme B and TNF-alpha but not FasL were expressed. CONCLUSIONS: Characterization of endothelial cell apoptosis in TEN and SJS is important to assess a factor worsening skin damage, with possible extension to other organs. It may also be useful for the development of novel therapeutic strategies.