The expression of thrombomodulin on sinusoidal endothelial cells was studied using the immuno-peroxidase method and both light and electron microscopy in patients with chronic viral hepatitis (type B: four cases; type C: 28 cases). Thrombomodulin was found on sinusoidal endothelial cells, especially on the surface in both type B and type C chronic hepatitis. There was no correlation between the level of thrombomodulin expression and clinical data including serum level of transaminase, and coagulating factors. The supernatant of liver tissue homogenate obtained from the patients showed a clear 80 kDa single band by western blotting. We concluded that the expression of thrombomodulin might be related to hepatic inflammatory responses in chronic viral hepatitis.