CYP2D6, CYP3A5, EPHX1, MPO, NQO1, NAT2, TS, XRCC1 and XPD polymorphisms were studied in a group of children with acute lymphoblastic leukaemia and CYP2D6 (del A and G/A), CYP3A5 (*3) and XPD (A/C) may have an important role in increasing the risk of ALL in children. The gene discussed is MPO; the disease is acute lymphoblastic leukemia.