To investigate the contribution of apoptosis, a major mechanism of cell death, in the growth of hepatocellular carcinoma, we analyzed both apoptosis and cell proliferation in human hepatocellular carcinoma. We used the terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labeling method and proliferative cell nuclear antigen staining, respectively. Among 21 hepatocellular carcinoma specimens examined, four were well, ten were moderately, and seven were poorly differentiated hepatocellular carcinoma. Terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labeling-positive cells in hepatocellular carcinoma were scattered individually or were sometimes clustered in the tumors. The terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labeling indices were 0.35 +/- 0.09, 0.81 +/- 0.29, and 1.9 +/- 0.94 in well, moderately, and poorly differentiated hepatocellular carcinoma, respectively. The proliferative cell nuclear antigen labeling indices were 6.6 +/- 0.9, 13.1 +/- 3.5, and 26.7 +/- 6.3 in hepatocellular carcinoma in the same respective order of differentiation. The differences in both terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labelling indices and proliferative cell nuclear antigen labeling indices (p < 0.05) were significant between well, moderately and poorly differentiated hepatocellular carcinoma. There was a positive correlation between the terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labeling and proliferative cell nuclear antigen labeling indices in hepatocellular carcinoma (r = 0.84, p < 0.001). This study showed that the proliferation rate and the incidence of apoptosis increased as the differentiation grade of hepatocellular carcinoma was lowered, suggesting a rapid turnover of cancer cells in the lower differentiation grades. Apoptosis may thus play an important role in the growth of hepatocellular carcinoma.