Motor neuron disease (MND) is caused by selective degeneration of motor neurons of the cerebral cortex, brain stem and spinal cord. Many genetic systems are thought to be involved in pathogenesis of this complex disease. A significant etiological factor of MND may be oxygen free radicals, which damage neuronal cells when they are present in high concentrations. Detoxication processes resulting in the formation of free radicals, which subsequently transformed into nontoxic products, are also critical for the disease development. The major participants of these processes are cytochromes P-450 (CYP2E1, CYP2D6), glutathione-S-transferases (GSTM1, GSTT1, GSTP1) and N-acetyltransferases (NAT2). To investigate a role of genes of detoxication system in development of MND, we study polymorphisms in these genes in 72 patients with MND from Moscow and controls from Russia. Significant statistical differences have been found in frequency of the alleles CYP2E1*1D, CYP2D6*4 and GSTM1(0/0) and genotypes homozygous for GSTM1 (0) between the study and control groups. The analysis of GSTT1, GSTP1 and NAT1 gene polymorphisms has revealed no between-group differences in distribution of different alleles and genotypes. The GSTP1*A/ GSTP1*A genotype was associated with a classical upper and lower motor neuron involvement and the GSTP1*A allele with predominant lower and upper motor neuron involvement.