In order to explore the role of ras oncogene in gastric carcinomas from Korean patients, we examined the frequency of point mutations all three ras oncogenes (Ki-, Ha-, and N-ras). A total of 57 DNA samples were prepared from 3 gastric carcinoma cell lines, 10 malignant ascites, and 44 frozen gastric tumor tissues. Exons 1 and 2 of each ras oncogene were amplified by polymerase chain reaction (PCR), and analyzed by single strand conformation polymorphism (SSCP) and direct sequencing. Mutated ras genes were detected in 6 out of 57 samples (10%). One cell line and 2 tumors showed a mutation at exon 1 of Ki-ras. N-ras mutations were also detected at exon 1 of 3 tumors. Histologically, all the ras mutation cases exhibited a diffuse phenotype. In summary, we performed a comprehensive analysis to investigate the mutation of all three ras oncogenes in gastric carcinoma. The results demonstrate infrequent mutations of Ki- and N-ras which may favor the development of diffuse type gastric carcinomas, implicating a different genetic pathway in diffuse and intestinal type gastric carcinomas.