The ability to document nuclear proliferation in the liver is essential to our understanding of hepatic regeneration and hepatocellular carcinoma. While numerous tests are available to provide such information in experimental animals, few can be applied to patients with liver disease. Ki-67 is a proliferating nuclear antigen present in replicating cells. Recent data indicates that staining for Ki-67 reflects nuclear proliferation in these tissues. To date, the technique has had only limited application to human liver tissues in formalin-fixed paraffin embedded tissue. In the present study, we documented Ki-67 staining in archival liver tissue from patients with mild chronic hepatitis, severe chronic hepatitis, inactive cirrhosis, hepatocellular carcinoma, and in normal livers. We found that Ki-67 staining was increased in patients with mild chronic hepatitis (labelling index 29 +/- 25), severe chronic hepatitis (labelling index 41 +/- 40), and hepatocellular carcinoma (labelling index 71 +/- 61), when compared to patients with inactive cirrhosis, (labelling index 1.4 +/- 3.1), and normal livers (labelling index 2.5 +/- 3.2). In conclusion, Ki-67 maybe useful tool to assess hepatocyte proliferation in formalin-fixed paraffin-embedded human liver tissue.