Inheritance of variant DNA repair genes is believed to influence individual susceptibility to the development of environmental cancer. However, the validity of the belief is dependent upon understanding the functions of the variant genes. Consequently, a variety of studies have been conducted to investigate the functions of variant DNA repair genes, e.g. using biomarkers. These studies on several representative polymorphic DNA repair genes are reviewed in this report. From a general overview, it appears that the biomarker investigations did not provide consistent observations. However, from a more careful evaluation, it is clear that the inconsistencies are probably caused by the use of populations and biomarkers that are not appropriate for investigating the repair activities of the genes. For example, the use of cigarette smokers and patients may not generate precise information for this type of investigations because these conditions can modify the functions of the investigated genes. Thus, the use of healthy non-smokers would be more appropriate. Other problems with these studies includes the small sample size used and the fact that some of the biomarkers used, such as sister chromatid exchanges, are not appropriate because the mechanisms for formation of the biomarkers and their biological significance are unknown. Nevertheless, the following conclusions can be derived from the review of the various biomarker studies that have been published. XRCC1 194Trp, OGG1 326Cys and APE1 148Glu probably have limited alterations in repair activities compared to the wild-type genotypes. XRCC1 399Gln and XRCC3 241Met are deficient in the repair of X-ray-, but not UV-light-induced chromosome aberrations, therefore the variant genes are defective in base excision repair. XPD 312Asn and XPD 751Gln are deficient in the repair of UV-light- but not X-ray-induced chromosome aberrations, therefore they are defective in nucleotide excision repair.