A polymorphism in exon 7 of the cytochrome P450 1A1 (CYP1A1) and A homozygous gene deletion at the glutathione S-transferase M1 (GSTM1) locus of genomic DNA isolated from peripheral blood were investigated for its relationship with lung, oral and urothelial cancer using the polymerase chain reaction (PCR) technique. As for the CYP 1A1 Val/Val genotype, 5 of 88 healthy controls (5.6%), 1 of 33 lung cancer patients (3.0%, P > 0.05, odds ratio 0.52, 95% confidence interval 0.21-17.3 with Ile/Ile Ile/Val type as base line), 4 of 32 oral cancer patients (12.4% P > 0.05, odds ratio, 2.37, 95% confidence interval 0.60-9.30) and 4 of 85 urothelial cancer patients (4.8% P > 0.05], odds ratio, 0.82, 95% confidence interval 0.21-3.16) were CYP 1A1 Val/Val types. The frequency of GSTM1 deletion genotype was 39.8% in the healthy controls and 45.5%, 50.0% and 61.2% in lung cancer, oral cancer and urothelial cancer patients, respectively. The frequency of GSTM deletion genotype was statistically increased in urothelial cancer patients (P < 0.05, odds ratio 2.38, 95% confidence interval 1.28-4.34). The odds ratio of combined genotypes of CYP1A1 Val/Val and GSTM1 deletion was 1.42 (95% confidence interval 0.12-16.8), 3.64 (95% confidence interval 0.47-27.9), 1.02 (95% confidence interval 0.14-7.53) in lung cancer, oral cancer and urothelial cancer patients, respectively. Thus, the GSTM1 deletion genotype as a host factor predisposing to urothelial cancer was proved in this study.