DNA mismatch repair (MMR) plays an important role in preserving genomic stability and reducing cancer risk. Environmental exposures to polycyclic aromatic hydrocarbons (PAHs) are believed to contribute significantly to carcinogenesis. PAHs are found in food, air, water and soil and upon bioactivation can form diol epoxides which are electrophilic in nature and can adduct to DNA, creating bulky PAH-DNA lesions. Preliminary data in the Buermeyer laboratory demonstrated that mutations induced by benzo[a]pyrene diol epoxide (BPDE) occur at higher rates in MLH1-deficient HCT 116+Ch2 cell line (30±7 mutations per 100 nM BPDE) versus a genetically matched MLH1-proficient line HCT 116+Ch3 cell line (10±4 mutations per 100 nM BPDE). I hypothesized that the role for MMR in suppressing mutation is a phenomenon generalizable to other cell lines. I measured BPDE-induced mutation rates in the parent cell line HCT 116, and in another genetically matched MSH6-proficient and -deficient set. I found an induced mutation rate of 30±5 mutations per 100 nM BPDE using HCT 116 cells, not significantly different from the induced mutation rate with HCT 116+Ch2 cells. In addition, we characterized mutants from HCT 116+Ch2 clones and identified 25 individual mutations with the predominance of G→T transversions.