PURPOSE: The aim of the present study was: (a) to determine the frequency of p53 mutations by single strand conformational polymorphism analysis of polymerase chain reaction products (PCR-SSCP), Non-Isotopic RNase Cleavage Assay (NIRCA) and immunohistochemical staining with monoclonal antibody; and (b) to compare the correlations among these methods. MATERIALS AND METHODS: Abberations of the p53 gene in 24 primary gastric carcinomas were examined by PCR-SSCP, NIRCA and immunohistochemical staining. Of these surgically resected gastric adenocarcinomas, 23 were advanced gastric carcinomas and 1 was early gastric cancer. Using PCR-SSCP and NIRCA, the presence of mutations in exons 4-9 was evaluated. Using the mouse specific anti-human p53 monoclonal antibody, we also looked for overexpression of the p53 protein in tissue sections. RESULTS: In 5 cases shifted bands were reproducibly identified by PCR-SSCP, and two mutations were identified in exon 4 and three in 5 & 6. The mutations of exon 4 were detected by NIRCA in 5 cases, exon 5 & 6 in 6 cases, and exon 7 in 2 cases. The p53 mutations detected by PCR-SSCP were also detected by NIRCA except one case. Thirteen of the tumor samples were positively stained with the monoclonal antibody for p53 protein. There was no correlation between p53 mutations detected by NIRCA and expression of p53 protein by immunohistochemical staining. CONCLUSIONS: Our results in this group of patients suggest that NIRCA is more sensitive than PCR-SSCP in detecting p53 mutations, and expression of p53 protein by immunohistochemical staining does not directely represent the genetic changes of p53 gene.