Hepatocyte growth factor (HGF) is a potent mitogen for various epithelial cells, including mature hepatocytes and renal tubular cells. Here, HGF mRNA was found to be markedly increased in non-injured kidney and spleen, when the liver or kidney in rats was injured by 70% partial hepatectomy or unilateral nephrectomy. HGF mRNA increased to 3–4 fold higher level than the normal in the kidney and spleen as well as in the remnant liver after partial hepatectomy. Similarly, HGF mRNA markedly increased in the spleen as well as in the remnant kidney after unilateral nephrectomy. These results suggest that the onset of injury to the liver or kidney may be recognized by distal non-injured organs by the signalling of a humoral factor and that HGF derived from these organs may be involved in the regeneration of liver or kidney, through an endocrine mechanism.