To elucidate the biological significance of the p53 gene expression in human hepatocellular carcinoma (HCC), the p53 protein was studied in 184 resected unifocal primary HCCs, including 102 small (< or = 5 cm) and 82 large HCCs (> 5 cm), using immunocytochemistry. The p53 mRNA expression was analyzed in 69 cases using Northern hybridization. The p53 protein, which was detected in 58 HCCs (31.5%), was overexpressed more frequently in HCC with elevated serum alpha-fetoprotein level (37.9 versus 25%, P < 0.04), in large HCC (39.0 versus 25.5%, P < 0.03), and in invasive HCC (35.1 versus 13.3%, P < 0.01). The overexpression of p53 protein closely correlated with p53 mRNA overexpression (75 versus 44.4%, P < 0.003), and p53 gene mutation (76.9 versus 19.2%, P < 1 x 10(-9)). HCCs with p53 protein expression (group A) and those negative for both p53 protein and mRNA expression (group B) had an unfavorable outcome, while HCC with no p53 protein but with p53 mRNA overexpression (group C) had the best outcome; the 4-year survival was 26.1, 26.3, and 62.5%, respectively. The p53 gene mutation was significantly higher in group A HCC (76.9%) than in groups B (27.3%) and C (23.5%), P < 0.0001. The results suggest that the p53 protein and mRNA expression patterns in HCC correlate with p53 gene mutation and tumor behavior and may serve as a molecular prognostic factor.