OBJECTIVE To estimate the relative risk for lung cancer associated with genetic polymorphism of the exon7 mutation (Ile/Val) of cytochrome P450 1 A1 (CYP1 A1) and glutathions S-transferase M1 (GSTM1) of Han population in Inner Mongolian, China.METHODS Allele-specific PCR and a multiplex PCR were employed to identify the genotypes of EXON 7 of CYP1A1 and GSTM1 in a case-control study of 219 lung cancer patients with bronchoscopy diagnosis and 230 matched controls free of malignancy.Pearson Chi-Square was used to show the significant difference and OR and 95% CI were calculated to estimate the risk of lung cancer.RESULTS The frequencies of the variant CYP1A1 (Val/Val) genotypes and GSTM1 (-) in lung cancer groups were higher than that in control groups (9.59% vs 4.35% and 56.16% vs 45.22%).The individuals who carried with CYP1A1 (Val/Val) or GSTM1(-) genotype had a significandy higher risk of lung cancer, the OR is 2.56 and 1.55 respectively.Stratified histologically the relative risk increased to 1.5-fold when the patients carried with two valine alleles than the ones carried one valine allele in cases of SCC.GSTM1 (-) genotype is also a risk of squamous cell carcinoma(SCC) (OR =1.74).Combinations of the CYP1A1 along with GSTM1 polymorphism were evaluated.The GSTM1 (-) and the valine allele have a synergetic effects in the susceptibility of lung cancer.Both carried GSTM1 (-) genotype, but the risk of susceptibility of lung cancer increased to 2-fold the ones who carried two valine alleles than those who carried with one valine allele.Considering ages and smoking status, the risk of lung cancer increased among the age of 51 to 65 who carried with CYP1A1 valine (one or two) or the age larger than 65 who carried with GSTM1 (-) genotype.The heavy smokers with CYP1A1 valine alleles and GSTM1 (-) have a high risk for lung cancer.CONCLUSION The valine allele of CYP1A1 and GSTM1 (-) were the risk factors of lung cancer especially for SCC of Inner Mongolia Han population.Heavy smoking is also relation to susceptibility to lung cancer.The influence of genotypes on the susceptibility of lung cancer may depend on the ages.There may be a synergetic interaction between CYP1A1 valine allele and GSTM1 (-) genotypes on the elevated susceptibility of lung cancer.So do those genotypes with heavy smokers.