Alterations in the expression of the RB tumour suppressor gene were found by Western immunoblot in three of seven hepatocellular carcinoma and hepatoblastoma cell lines. Abnormalities were detected by single-strand conformation polymorphism (SSCP) within exons 17-21 in RB cDNA from two of these three cell lines and within exons 20-21 in the third cell line. In these three cell lines with abnormal RB expression, abnormal expression of the p53 tumour suppressor gene was also found, apparently the product of a mutant gene. Thus, mutations within the RB gene (or splice-site mutations with exon-skipping) and apparent mutations of the p53 gene together may have contributed to the development of three of these tumours or to the establishment of these cell lines.