Cytochrome P450 1A1 (CYP1A1) is involved in the production of arachidonic acid-derived vasoactive substance. We hypothesized that CYP1A1 polymorphism might be related to pathological conditions associated with cerebral infarction (CI). We investigated the effect of genetic polymorphism in the 3'-flanking region (T6235C) of CYP1A1 gene in 353 patients with CI and 376 controls. The distributions of T6235C CYP1A1 genotypes in patients with (TT: 36.0%; TC/CT: 64.0%; n = 353) and without CI (TT: 44.7%; TC/CT: 55.3%; n = 376) indicate that the C allele is associated with CI (P = 0.017, odds ratio (O.R.) = 1.44; 95% confidence interval (C. I.) = 1.07-1.94). Furthermore, we examined whether the glutathione S-transferase (GST) gene, which is one of detoxification enzyme, influence the risk of CI. GST M1 null genotype increased the relative risk for the CI in the subjects with the CYP1A1 C allele (P = 0.015, O.R. = 1.47; C. I. = 1.08-2.00). We conclude that T6235C CYP1A1 polymorphism is a risk factor for the development of CI and suggest that GST polymorphism contribute to the odds of CI.