The incidence of homozygote deletion of glutathione S-transferase genes M1 and T1 (null genotypes; or GSTM1"-" and GSTT1"-") was studied in breast cancer patients living in Altai Krai. DNA was isolated from blood samples of 695 breast cancer patients (291 patients with familial cancer and 404 patients with sporadic cancer) and 263 women without history of tumor diseases. The frequency of GSTM1"-" and GSTT1"-" genotypes was estimated in breast cancer patients (47.2 and 19.1%, respectively) and non-cancer participants (46.8 and 19.0%, respectively). No differences were found in the frequency of genotypes. The frequency of genotype combination GSTM1"-"+GSTT1"-" in patients with sporadic breast cancer (11.6%, 47 of 404 patients) was higher than in the control (6.1%, 16 of 263 patients; OR=2.03; 95% CI=2.09-3.83; p=0.02). The genotype frequency of genes in the control group did not differ from that in European residents of the Caucasian race.