Human Chk1 and Chk2 are DNA damage-activated protein kinases that function as downstream mediators of ataxia-telangiectasia mutated (ATM), which is involved in G(2)/M cell cycle arrest. To clarify the relation between the expression of Chk1/Chk2 and p53 gene status in human gastric carcinomas, we examined expression of Chk1, Chk2 and p53 proteins in 87 gastric carcinomas by Western blotting and immunohistochemistry. We found a significant correlation between the expression levels of Chk1 and p53 proteins in gastric carcinomas (p = 0.016). Significant statistical association was also observed between levels of Chk2 and p53 proteins (p = 0.00024). To clarify the genetic alterations of p53 in gastric carcinomas, we performed PCR-SSCP analysis on 47 gastric carcinomas. Although we found that 5 of 7 (71%) gastric cancers expressed elevated levels of Chk1 had p53 mutation, there was not a statistically significant correlation between expression of Chk1 and genetic status of p53. We also found that 7 of 11 (78%) gastric carcinomas expressed elevated levels of Chk2 had p53 mutation, and this correlation was significant (p = 0.0157). We used a highly quantitative 5' nuclease fluorogenic RT-PCR method (TaqMan) to analyze the expression of Chk2 mRNA in 22 gastric carcinomas. Chk2 mRNA expression was higher in gastric carcinomas with p53 mutations compared to those harboring wild-type p53. A significant association was recognized between the expression of Chk2 mRNA and p53 mutational status (p = 0.031). Our findings support the hypothesis that expression of Chk2 protein is increased in gastric carcinomas with mutant p53. Chk1 and Chk2 may play important roles in the checkpoint function in human gastric carcinomas harboring p53 mutation when their functions are preserved to prevent cell cycle progression.