Mutations in the p53 gene are frequent genetic alterations in human hepatocellular carcinoma. We have examined 38 hepatocellular carcinoma cases from Taiwan for the presence of p53 alterations in exons 5-8 of the gene using the single-stranded conformational polymorphism method and direct sequencing of polymerase chain reaction products. Using the single-stranded conformational polymorphism method, we found mutations in 16 (42.1%) cases. Twelve mutations were found in exon 5, three in exon 7, and one in exon 8. No mutations were found in exon 6. Sequencing of polymerase chain reaction products showed that all mutations in exon 5 were clustered at codon 166 and were T/A transversions resulting in an amino acid change from serine to threonine, identifying a new hot-spot for point mutations in the p53 gene. The mutations in exon 7 were all at codon 249, and were G/T transversions leading to an amino acid change of arginine to serine. Finally, the mutation at exon 8 was a G-to-T transversion at codon 286 leading to a stop codon. These data indicate that mutations of the p53 gene may be important in the development of human hepatocellular carcinoma and that, in contrast to other tumors, the mutations of the p53 gene in hepatocellular carcinomas can be clustered in a specific codon of the gene.