Hepatocyte growth factor, a potent mitogen for mature hepatocytes in vitro, seems to function as a hepatotrophic factor for liver regeneration. We examined the mitogenic effect of hepatocyte growth factor on mouse liver in vivo. The labeling index of hepatocytes was markedly increased when recombinant human hepatocyte growth factor was injected intravenously into mice subjected to 30% hepatectomy (control, 1.7% +/- 0.1%; 1 microgram hepatocyte growth factor, 6.4% +/- 1.3%; 5 micrograms hepatocyte growth factor, 18.3% +/- 0.2%) and into mice administered carbon tetrachloride (control, 12.7% +/- 1.0%; 1 microgram hepatocyte growth factor, 26.3% +/- 2.8%) or alpha-naphthylisothiocyanate (control, 0.4% +/- 0.1%; 1 microgram hepatocyte growth factor, 3.8% +/- 1.1%; 5 micrograms hepatocyte growth factor, 14.2% +/- 2.0%). In addition, weights of the remnant livers in mice given hepatocyte growth factor 60 hr after 30% hepatectomy were significantly greater than those of untreated control mice (control, 0.93 +/- 0.04 gm; 5 micrograms hepatocyte growth factor, 1.06 +/- 0.04 gm). Hepatocyte growth factor prevented any marked increase in the serum levels of liver enzymes and bilirubin when it was administered to mice also treated with alpha-naphthylisothiocyanate (control: ALT, 394 +/- 278 IU/L; lactate dehydrogenase, 2,644 +/- 1,109 IU/L; bilirubin, 9.6 +/- 2.6 mg/dl; and 5 micrograms hepatocyte growth factor: ALT, 135 +/- 7.9 IU/L; lactate dehydrogenase, 1,672 +/- 626 IU/L; bilirubin, 1.0 +/- 0.8 mg/dl). Our findings show that intravenously injected hepatocyte growth factor stimulates the growth of hepatocytes in mouse liver and protects the integrity of hepatocytes in vivo against hepatitis caused by hepatotoxin.(ABSTRACT TRUNCATED AT 250 WORDS)