PURPOSE To investigate the methylation of p53 gene in human thyroid carcinoma. METHODS The DNA of 12 thyroid carcinomas and 5 adjacent tissues of thyroid carcinoma were digested by restriction endonuclease enzymes Hap I and Msp I . Polymerase chain reaction (PCR) followed by agarose gel electrophoresis was used to detect the methylation in the exon 5 of p53 gene. RESULTS 5'-CCGG-3' site was methylated at the exon 5 of p53 gene in 9 thyroid carcinomas. However hypomethylation was found to exist in 5 adjacent tissues of thyroid carcinoma. CONCLUSION Hypermethylation of p53 gene plays an importan...