Styrene oxide (SO), ethylene oxide (EO) and gamma-radiation (G) are agents with a well-described metabolism and genotoxicity. EPHX1 and GSTs play an important role in the detoxification of electrophiles and oxidative stress. Enzymes involved in base excision repair (hOGG1, XRCC1), in rejoining single strand breaks (XRCC1) and in repair of cross-links and chromosomal double strand breaks (XRCC3) might have an impact on genotoxicity as well. In this study we assessed the dose-dependent effect of genetic polymorphisms in biotransforming (EPHX (Tyr113/His113 and His139/Arg139), GSTP1 (Ile105/Val105), GSTM1 and GSTT1) and DNA repair enzymes (hOGG1 (Ser326/Cys326), XRCC1 (Arg194/Trp194, Arg280/His280, Arg399/Gln399), XRCC3 (Thr241/Met241)) on the induced genotoxicity. Peripheral blood mononuclear cells from 20 individuals were exposed to 3 doses per agent (+control). Genotoxicity was evaluated by measuring comet tail length (TL) and micronucleus frequencies in binucleated cells (MNCB). Dose-dependent DNA damage was found for all agents and end-points, with the exception of MNCB induced by EO. Repeated measure ANOVA revealed a significant contribution of hOGG1 and XRCC3 genotypes to the inter-individual variability of TL and MNCB in cells exposed to EO and G. Homozygous hOGG1326 wild cells showed significantly lower EO-induced TL than the heterozygous cells. Significantly higher TL and MNCB were found in EO-exposed cells carrying the XRCC3(241)Met variant and the influence on TL was more pronounced at higher dose. In G-irradiated cells, TL was significantly higher in the hOGG1326 homozygous wild types compared with mutated genotypes. The influence of hOGG1326 on TL was borderline dose-dependent. We conclude that the influence of genetic polymorphisms of enzymes involved in DNA repair on induced genotoxicity depends on exposure dose.