Angiosarcoma of the liver is a rare malignant tumor which has been associated with occupational exposure to vinyl chloride (VC). We have determined by ELISA the level of von Willebrand factor (vWf) in the serums of 107 VC-exposed workers, active or retired, and of 133 blood donors used as controls. The vWf level was slightly but significantly higher in the VC-exposed group than in the control group (P = 0.035). Seventeen VC-exposed workers exhibited a raised level of vWf, with no biochemical sign of hepatic disturbance, nor any evidence of illness; only one of them exhibited elevated alkaline phosphatase and gamma-glutamyl transpeptidase values. The vWf serum level of 3 patients with hepatic angiosarcoma associated to VC-exposure was markedly elevated. These increased levels of vWf in VC-exposed workers most likely reflect an increased activity of liver endothelial cells; whether an elevated level of vWf could be associated with increased risk of developing liver angiosarcoma remains to be determined.