Hepatocyte growth factor (HGF) is a potent stimulator of DNA synthesis in cultured hepatocytes. To determine whether HGF has any activity in vivo, we have tested HGF in rats in which intrahepatic cholestasis was induced by acute administration of alpha-naphthylisothiocyanate (ANIT). The hepatotoxic effects of a single injection of ANIT were manifested 48 h later as large increases in serum bilirubin, alanine aminotransferase, aspartate aminotransferase, and alkaline phosphatase. These biochemical changes were accompanied by widespread periportal edema, hypertrophy of bile duct epithelium, and randomly scattered areas of liquifaction necrosis in the hepatic parenchyma. The increases in bilirubin, alanine aminotransferase, aspartate aminotransferase and alkaline phosphatase were markedly attenuated when HGF was administered 30 min before ANIT and again at 6, 12, 24, 30, and 36 h after ANIT. In addition, this HGF dosing regimen completely prevented the occurrence of parenchymal lesions, although it had no effect on periportal histopathology. The effect of ANIT was dose dependent; a maximal response was observed at 320 micrograms/kg per injection, with an intermediate response at 105 micrograms/kg. Delaying the administration of HGF until 12 h after ANIT was as effective as when administration was begun 30 min before ANIT. Taken together these results show that HGF can prevent some aspects of ANIT hepatotoxicity.