Association between genetic polymorphism in GSTM1 and GSTT1 and frequency of chromosomal aberrations in the workers occupationally exposed to uranium during 1-25 years in Tselinniy mining/milling complex in the North Kazakhstan was investigated. It was found that the frequency of chromosomal aberrations in uranium workers was significantly higher than in matched control, being correlated with the duration of exposure. No association between frequency of chromosomal aberrations and polymorphism for each gene (GSTM1 and GSTT1) was observed, whereas frequency of chromosomal aberrations in the homozygous carriers of null alleles of both GSTM1 and GSTT1 genes was higher than in the homozygous carriers of normal alleles.