Vinyl chloride production workers, with or without known liver disease, are being admitted to the Clinical Center for detailed evaluation of hepatic status. Sensitive liver function tests, including dye clearance studies, radiolabeled bilirubin kinetic studies and studies of the plasma clearance of bile acids, are being employed in an attempt to establish a screening regimen which will be sensitive enough to detect early vinyl chloride associated liver injury. In addition, detailed studies of hepatic morphology and hemodynamics are being conducted in these workers employing such techniques as peritoneoscopy, percutaneous liver biopsy, and hepatic vein catheterization and splenoportography. Histologic materials obtained by biopsy are being examined by both light and electron microscopic techniques. In addition to patients actually studied at the NIH, the NIH are serving as a clearing house for the examination of histologic materials from workers with vinyl chloride associated hepatic fibrosis and angiosarcoma submitted from other institutions.