The polymorphism of some genes (GST, CYP2E1, ALAD, EPHX1 and NQO1) was studied by De Roos et al.10,17 and Rajamaran et al.16, since they participate on the metabolism of many chemical substances, such as lead, aromatic hydrocarbons and other solvents, which roles have been investigated in the etiology of numerous brain tumors.