Carcinogenicity of 1,3-butadiene (BD) has been linked to its metabolic activation of genotoxic epoxides. The inherited variations in the activity of BD-metabolizing enzymes may be responsible for individual differences that modulate the effects of BD exposure. In this study, 40 Italian subjects (30 BD-exposed workers and 10 clerks) were investigated to evaluate the role of genetic polymorphism of cytochromes P450 2E1, microsomal epoxide hydrolase, glutathione transferases GSTM1, GSTP1, GSTT1, and alcohol dehydrogenase, on urinary N-acetyl-S-(3,4-hydroxybutyl)-L-cysteine (MI) and hemoglobin N-(2,3,4-trihydroxybutyl)-valine adducts (THBVal). Median urinary MI and THBVal levels were 1.71 mg/g creatinine and 37.0 pmol/g globin in BD-exposed workers (exposure range, 4-201 microg/m(3)) and 1.42 mg/g creatinine and 35.3 pmol/g globin in unexposed subjects. No difference between the two groups was observed. Among all subjects, MI and THBVal levels were significantly correlated (r = 0.333). Smoking positively influenced the formation of THBVal. Higher THBVal levels were found in subjects with GSTM1 null and GSTT1 null genotypes; borderline influences were also noticed for CYP2E1(G(-35)T). An additive effect of combined polymorphisms for CYP2E1, GSTM1, and GSTT1 genes on the THBVal levels was suggested. A multiple linear regression analysis, where each factor contributed significantly, correlated THBVal levels with smoking, CYP2E1(G(-35)T), GSTT1, and GSTM1 genotypes (r = 0.698). Our results indicate that the THBVal level is influenced by genotypes, and that the analysis of combined polymorphisms may be the key to a better understanding of the role played by polymorphism of BD-metabolizing enzymes.