1. Previous studies have established that genetic alterations in glutathione S-transferase enzymes may change the ability of the airway to deal with toxic substances and increase the risk of asthma. The present study analysed the association between asthma and GSTA1, GSTO1 and GSTO2 gene polymorphisms. 2. The GSTA1*-69C/T, GSTO1*A140D and GSTO2*N142D polymorphisms were detected by polymerase chain reaction-restriction fragment length polymorphism, whereas the GSTO1*E155del polymorphism was detected using the confronting two-pair primer method. 3. Distribution of the GSTA1*-69C/T genotype differed significantly between asthmatics and controls. Subjects with at least one allele -69T in the GSTA1 genotype have an increased risk of asthma (odds ratio (OR) 3.45; 95% confidence interval (CI) 1.80-6.62). The distribution of the GSTO1 genotype was nearly equal between the control group and asthmatics, however, the distribution of the GSTO2 gene differed significantly between asthmatics and controls (Chi-squared test). Subjects who had the GSTO2 homozygous D142 genotype were found to have an increased risk of asthma (OR 5.91; 95% CI 1.80-19.42). 4. The results show a potential association between the GST genes and asthma. This is particularly significant given that, in the literature, there are no epidemiological studies on alpha and omega classes of glutathione transferases in asthma.