To evaluate the influence of individual susceptibility factors on the level of polyaromatic (PAH) hydrocarbon DNA adducts and hypoxanthine guanine phosphoribosyl transferase (HPRT) mutants in peripheral lymphocytes, 70 coke-oven workers exposed to PAH were genotyped for four metabolic enzyme polymorphisms of potential importance in PAH metabolism. The examined genetic polymorphisms concerned glutathione S-transferases M1 (GSTM1; gene deletion; 96 workers), T1 (GSTT1; gene deletion), P1 (GSTP1; Ile-->Val substitution at codon 104 or Ile-->Val at codon 104 and Val-->Ala at codon 113), and microsomal epoxide hydrolase (EPHX; Tyr-->His substitution at codon 113 and His-->Arg at codon 139). The workers were classified in a high- and low-exposure group on the basis of urinary concentration of 1-pyrenol. The GSTM1 null genotype increased the number of DNA adducts in smoking coke-oven workers with high PAH exposure. DNA adducts were affected by PAH-exposure in non-smokers and in GSTM1 null smokers and by smoking in GSTM1 null individuals. In a multiple linear regression analysis, the interaction of the GSTM1 genotype was statistically significant (p = 0.04) with smoking (yes/no) and of borderline significance (p = 0.06) with PAH-exposure (high/low). As smoking also increased urinary 1-pyrenol, the genotype modification seemed to concern DNA adducts due to smoking rather than occupational exposure. GSTT1 positive individuals showed an elevated level of DNA adducts in comparison with GSTT1 null subjects (p = 0.04), and EPHX genotypes associated with slow hydroxylation reaction yielded a higher (p = 0.05) HPRT mutant frequency than fast EPHX genotypes; these findings were, however, based on small numbers of subjects and need to be clarified in further studies. In conclusion, our findings indicate that homozygous deletion of GSTM1 results in an increased sensitivity to genotoxic PAHs in tobacco smoke, which is seen as an increase in aromatic DNA adducts in blood mononuclear cells.