We examined the expression of mutant p53 gene products in primary malignant epithelial tumors of the liver. Fourteen of 68 hepatocellular carcinomas, one of seven hepatoblastomas and one of nine intrahepatic cholangiocarcinomas showed nuclear staining for p53 proteins. None of the surrounding non-tumorous tissues expressed nuclear staining. The detection of p53 proteins in tumor cells was significantly higher in hepatocellular carcinomas of Oriental patients (31.6%) compared to non-Orientals (6.7%, p < 0.015). No significant differences were seen in p53 antigen expression between hepatitis B and non-hepatitis B associated hepatocellular carcinomas in Oriental patients. These results suggest a role for other environmental factors, such as aflatoxin, in the etiology of p53 mutation in hepatocellular carcinoma in Oriental patients.