The phenotype characteristics of bronchial asthma in 94 children from the Ivano-Frankivsk region with different variations of allelic gene polymorphism of the 2-nd phase of xenobiotics detoxification: GSTM1 and GSTT1 have been studied. The association between the polymorphism of such genes, liability to developing and severity of asthma in children has been described. It has been determined that the implementation of asthma as ecodeterminated pathology is affected by individual variations of metabolic activity of genes of xenobiotics detoxification. It's proved that in patients with uncontrolled asthma genotypes del/del on both genes glutathione-S-transferase (GSTM1 and GSTT1) were met much more common.