We examined hepatocyte growth factor-producing organs in normal and carbon tetrachloride-treated Japanese monkeys, a species more related to human beings than rats, by measuring hepatocyte growth factor protein and hepatocyte growth factor mRNA in various tissues. Hepatocyte growth factor protein and hepatocyte growth factor mRNA levels were determined by use of an enzyme-linked immunosorbent assay for human hepatocyte growth factor and Northern-blot analysis using human hepatocyte growth factor cDNA as a probe, respectively. Although very slight amounts of hepatocyte growth factor protein were found in various organs of normal monkeys, the hepatocyte growth factor protein levels were remarkably increased only in the livers and spleens of carbon tetrachloride-treated monkeys. Hepatocyte growth factor mRNA was distinctly detected in the livers, spleens, lungs, intestinal tracts, adrenal glands and aortas of normal monkeys. After the administration of carbon tetrachloride, the hepatocyte growth factor mRNA levels in the liver, spleen and gastrointestinal tract were markedly increased; the level in the lung was unchanged, differing from the findings in rats; and the levels in adrenal gland and aorta were unaltered. These results indicate that the liver is an important hepatocyte growth factor-producing organ in monkeys during liver regeneration and that hepatocyte growth factor induced in the liver may stimulate hepatocyte proliferation by way of a paracrine mode.