Several polymorphic genes including those encoding for glutathione S-transferases (GST) have been reported to be involved in modifying lung cancer risk in smokers. The gene GSTM1 is frequently deleted in humans and a possible association between the null genotype and lung cancer risk is controversial. Another polymorphic gene of the same supergene family, GSTT1, is also involved in the detoxification of some environmental carcinogens. Both genes were genotyped in (a) a group of lung cancer patients (n = 160); (b) a group of healthy smokers (n = 120); (c) a group of blood donors from the general population (n = 192). All patients and controls were Northwestern Mediterranean Caucasians. The results show that the GSTM1 null genotype (GSTM1*0/GSTM1*0) was slightly over represented in the lung cancer patients (frequency of 58%; OR: 1.40, 95% CI: 0.74-2.61, referred to healthy smokers). The histological type most clearly modified was small cell carcinoma (frequency of 62.2%, OR: 1.91, CI: 0.78-4.69). The subdivision of the patients with one or two copies of the GSTM1 gene according to a GSTM1*A, GSTM1*B or GSTM1*A/B genotype (frequencies of 28.2%, 11.2%, 2.5% respectively) revealed no significant differences between the cases and both control groups. The frequency of the deleted GSTT1 genotype among the lung cancer patients (24%) was not significantly increased (OR: 1.08, CI: 0.57-2.05, referred to healthy smokers). The results showed that 14.4% of the patients presented homozygous deletion of both GSTT1 and GSTM1 (12.5% among healthy smokers) suggesting no potentiation between null genotypes for lung cancer risk.