The molecular mechanisms of the carcinogenic process of gastric cancer have not been fully understood yet. In order to know whether c-Ha-ras gene is being involved in the process of gastric carcinogenesis, 8 gastric cancer cell lines, 8 cases of gastric cancer and same number of adjacent dysplasia were analyzed for the presence of mutation at codon 12, 13 and 61 of the c-Ha-ras gene by using polymerase chain reaction (PCR) and mutant-specific oligonucleotide hybridization. Point mutations at codon 12 of the c-Ha-ras gene were found in 2 out of 8 gastric cancer and dysplasia samples in one case, but we found no mutation at codon 13 or 61 of the c-Ha-ras gene. These results suggest that the frequency of mutation of the c-Ha-ras gene detected by sensitive PCR technique is low indeed, however it would be notable that such a genetic change has been detected in the dysplastic lesion of the gastric cancer patient.