Endothelium damage is associated with thrombotic risk in a variety of diseases including atherosclerosis, gram negative sepsis, viral infections and neoplastic disease. Therefore, it appears necessary to find a mean for the clinical investigation for such a damage. Among the markers of these cells, thrombomodulin which is a membrane glycoprotein, seems to be of great interest for this purpose. Actually, thrombomodulin is also found in plasma, following an endothelial lesion. Plasma levels of thrombomodulin are increased in a certain number of pathologies associated with endothelium lesion: atheromatous arterial disease, disseminated intravascular coagulation syndrome and also in systemic lupus erythematosus where the levels of plasma thrombomodulin are related to the severity of the pathology. Moreover, previous in vitro studies confirm the fact that the release of thrombomodulin from the endothelial cell membrane occurs during the course of injury by activated leukocytes or hydrogen peroxide. So, one can suppose a prospective interest in the measurement of plasma thrombomodulin as a diagnostic tool for the approach of endothelium damage.