Cancer susceptibility differences may be attributed in part to genetic variation in genes involved in metabolism of environmental procarcinogens. Increased risks for some cancers have been linked to polymorphisms in certain phase I and II genes, and have been associated with genomic instability and chromosomal aberrations. Aberration frequencies in general, and stable aberration frequencies (translocations and insertions) in particular, are used as biomarkers for disease. Thus, knowledge of the genetic factors that influence the frequency of stable aberrations in a normal population is important for cancer risk determination. In this work, genotypes for a number of xenobiotic enzymes (CYP1A1, CYP2D6, GSTM1, GSTT1, GSTP1, NAT1, NAT2and epoxide hydrolase) and stable aberration frequencies were determined for 65 normal individuals aged 19-77 years. The population was divided at age 60 years for analysis because there was a significant difference in stable aberration frequencies between these groups. Subjects with low levels (0-66th percentile) of stable aberrations were compared to those with high levels (67th percentile and above). Of all the genotypes studied, onlyNAT2showed a notable difference between the high and the low stable aberration groups in the percentage of polymorphisms observed, and this was seen only in the older subjects group. All individuals in the older-high stable aberration group wereNAT2rapid acetylator smokers.NAT2slow acetylator smokers had significantly lower stable aberration frequencies compared to theNAT2rapid acetylator smokers. Following previous work showing an increased risk of cancer associated with high levels of aberrations (above the 66th percentile), we hypothesize that smokers with theNAT2rapid acetylator genotype may be at an increased risk for cancer.