The authors presented a comparative study of polymorphous loci Ile105Val and Ala114Val in GSTP1 gene, C609T and C464T in NQO1 gene, Pro197Leu in GPX1 gene of workers engaged into ethylbenzene-styrene (JSC "Salavatnefteorgsintez") and of apparently healthy individuals without occupational exposure to toxic chemicals. The same polymorphous markers were studied in workers differentiated according to health state. Occurrence of genotypes Ile/ Val of GSTP1 gene, Pro/Leu in GPX1 gene in the main group were lower vs. that in the reference one. Occurrence of CC genotype of polymorphous locus of C609T in NQO1 gene in the examinees exceeded that in the reference group. Distribution analysis of haplotypes of NQO1 and GSTP1 revealed high occurrence of *A haplotype of GSTP1 gene and low occurrence of *B haplotype in the main group vs. the reference one. The authors proved that molecular genetic marker of toxic liver affection is a heterozygous genotype of Pro/Leu in GPX1 gene and a combination of II/PL/CC genotypes of polymorphous markers Ile105Val in GSTP1 gene, C609T in NQO1 gene, Pro197Leu in GPX1 gene.