We studied the relationship of serum levels of human hepatocyte growth factor (hHGF) to causative viruses and clinical features in 63 patients at our hospital with serologically diagnosed acute viral hepatitis. Serum levels of hHGF were not correlated with the type of hepatitis virus (A, B, and C) during the acute phase (p < 0.60) but were correlated with results of the hepaplastin test (p < 0.01). Furthermore, the difference in serum levels of hHGF between severe (levels on hepaplastin test < 40%) and nonsevere cases of hepatitis was significant (p < 0.001), and serum levels of hHGF became normal as levels of alanine aminotransferase decreased. However, serum levels of hHGF in prolonged cases of hepatitis (time until normalization of alanine aminotransferase > 13 weeks) tended to be slightly lower than in nonprolonged cases (p < 0.47). These results suggest that serum levels of hHGF are useful to determine the prognoses of patients with severe hepatitis and to estimate the time until liver damage heals.