The genetic polymorphism of glutathione- S-transferase M1 (GSTM1) and glutathione- S-transferase T1 (GSTT1) genes and the cytochrome P4501A1 gene responsible for xenobiotic conjugating enzymes of the phase II and phase I detoxification system were studied by PCR-RFLP in the blood spots of 109 patients with atopic bronchial asthma and 90 healthy individuals. GSTM1 gene deletion (GSTM1(0/0)) was detected in 47.8% of individuals in the control group and in 76.1% of asthmatic patients. Individuals without the GSTM1 gene were at approximately 3.5--fold higher risk of developing asthma. The proportion of GSTT1(0/0) genotypes was significantly higher in the group of asthmatics (67.0%) than in controls (23.3%). The proportion of individuals with a deficiency in both GSTM1 and GSTT1 gene activity was more than four times higher in asthmatic patients than in the control group (54.1% and 12.2%, respectively). The frequency of the Ile-Val polymorphism of the CYP1A1 gene was similar in controls and asthmatic patients. This study shows the association of atopic bronchial asthma with GSTM1(0/0), GSTT1(0/0) genotypes.