Defects in the activity of the PTEN gene, a tumor suppressor, are implicated in many types of cancer in humans. However, not all mediators of PTEN signaling pathways have been clarified, and, during efforts to identify such molecules, we previously induced expression of the DUSP1 and BTG1 genes by introducing exogenous PTEN into endometrial cancer cell lines. In the course of analyzing these two genes for mutations in ovarian carcinomas, we identified a novel single-nucleotide polymorphism (SNP) in the DUSP1 gene, and three novel SNPs in the BTG1 gene, and we have established their allelic frequencies in a Japanese population sample. These polymorphic sites will be useful for detecting losses of heterozygosity (LOH) in tumors and for examining latent associations between specific alleles and disease susceptibility.