Genetic polymorphism of xenobiotic metabolizing enzymes responsible for individual susceptibility to different environmental factors was examined in a cohort of petrochemical workers occupationally exposed to adverse action of chemical compounds. Molecular genetic analysis of the 1462V mutation in exon 17 of the CYP1A gene demonstrated close similarity between the genotype and allele frequency distribution patterns in the industrial and control groups. No association between the CYP1A polymorphic alleles and genotypes and the duration of service and concomitant diseases was observed. The odds ratio of the disease development in the workers carrying heterozygous CYP1A1 mutant allele was 2.2. Analysis of the STM1 gene polymorphism demonstrated a decrease in the frequency of the homozygous deletion carriers in the workers compared to the control group. There were no substantial differences between the industrial and control groups with respect to the frequencies of rapid and slow acetylator genotypes revealed at the analysis of the NAT2 gene polymorphism. However, considering the concomitant diseases, in the corresponding industrial subgroup a clear trend towards lower frequency of rapid acetylators was demonstrated. In addition, the odds ratio of the disease development for the workers with slow acetylator phenotype was 1.7.