The aim of this study was to evaluate whether there is endothelial dysfunction in patients with cirrhosis and to detect the mechanism that may account for it. We measured plasma levels of von Willebrand factor (vWF), a marker of endothelial perturbation, and endotoxin, which releases vWF from endothelial cells in vitro, in 32 patients (18 men, 14 women, aged 39-70 years) with cirrhosis classified as mild (class A, n = 10), moderate (class B, n = 16), or severe (class C, n = 6) according to Child-Pugh's classification. vWF antigen (P < .0001) and endotoxemia (P < .0001) progressively increased from A to class C; but the increase of vWF antigen was not strictly related to liver failure, as shown by the lack of correlation between vWF and several indexes of liver protein synthesis. Analysis of the vWF subunit showed no sign of proteolytic fragmentation of the molecule. Multimeric analysis indicated intact vWF multimeric structure. In all patients, there was a strong correlation between vWF antigen and endotoxemia (rho = .92; P = .0001). In 20 selected patients, vWF antigen and endotoxemia were measured before and after 7 days of standard therapy (n = 10) or standard therapy plus nonabsorbable antibiotics. There was a significant decrease of vWF antigen (P < .02) concomitantly with the decrease of endotoxemia (P < .006) in patients taking nonabsorbable antibiotics. Human umbilical vein endothelial cells incubated in vitro with 125 to 500 pg/mL endotoxin released vWF antigen into the medium dose dependently. These results demonstrate that there is endothelial perturbation in cirrhosis and that endotoxemia may play a key role in its occurrence.