【Objective】 This study was aimed to assess the frequency of functional polymorphism by the genes of xenobiotic detoxication in the population living in the unfavorable environmental conditions.【Method】 The samples of DNA from lymphocytes of venous blood of 200 healthy persons living in the region with unfavorable environmental conditions characterizing with high concentration of nitrates(more than 50 mg/dm3) in the drinking water were examined for the frequency of slow(S) alleles of NAT2 gene.【Result】 The frequency of slow(S) alleles of NAT2 gene was 63.5% whereas slow alleles of GSTM1 gene were determined in 68.5 %cases.The ratio between slow and fast alleles was 1:1.3 for NAT2 gene and 1:1.25 for GSTM1 gene.【Conclusion】 The frequency of functionally defective alleles of NAT2 and GSTM1 genes in the population living in the unfavorable environment conditions is not higher than that in the general Caucasian population.Every sixth resident of such regions has high risk of environment related diseases. 【Objective】 This study was aimed to assess the frequency of functional polymorphism by the genes of xenobiotic detoxication in the population living in the unfavorable environmental conditions. 【Method】 The samples of DNA from lymphocytes of venous blood of 200 healthy persons living in the region with unfavorable environmental conditions characterizing with high concentration of nitrates (more than 50 mg / dm3) in the drinking water were examined for the frequency of slow (S) alleles of NAT2 gene. gene was 63.5% of the slow alleles of GSTM1 gene were determined in 68.5% cases.The ratio between slow and fast alleles was 1: 1.3 for NAT2 gene and 1: 1.25 for GSTM1 gene. 【Conclusion】 The frequency of functionally defective alleles of NAT2 and GSTM1 genes in the population living in the unfavorable environment conditions is not higher than that in the general Caucasian population. Every sixth resident of such regions has a high risk of environment related diseases.