Glutathione S-transferases are possibly related to the detoxification of many xenobiotics involved in the etiology of cancer. To investigate the role of the glutathione S-transferase M1 deletion (GSTM1-null) in lung cancer, the polymerase chain reaction was used to determine the GSTM1 genotypes of lung cancer patients (n=101) and hospital (n=206) in a Turkish population. The prevalence of the GSTM1-null genotype in the case group was 48%, compared to 18% in the control group, giving an odds ratio (OR) of 4.14 (95% confidence interval [CI]=2.36-7.27). The analysis of patients by histologic type of lung cancer (10% adenocarcinoma, 43% squamous cell carcinoma, 26% small cell carcinoma, and 11% large cell carcinoma) showed no association between histopathologic type of lung cancer and GSTM1-null genotype. When the interaction between the GSTM1-null genotype and smoking status was analyzed, among the 67 smokers, the GSTM1-null genotype was found in 37 (55%) with an OR of 2.58 (95% CI=1.00-6.73) indicating a significant association. However, no association was found between smoking exposure (<30 and > or =30 packs/year) and GSTM1-null genotype. We conclude that, in this study the null GSTM1 genotype is an independent risk factor for the development of lung cancer for Turkish population.