They were examined for presence of m-RNA of fusion genes BCR/ABL, MLL/AF4 and TEL/AML1 by reverse transcriptase-polymerase chain reaction (RT-PCR) method.     ///    BCR/ABL positivity was found in 2.5% (7 out of 240) and TEL/AML1 in 21.7% (41 out of 189) cases.     ///    "[Detection of BCR/ABL, MLL/AF4 and TEL/AML1 hybrid genes and monitoring of minimal residual disease in pediatric patients with acute lymphoblastic leukemia].. "    ///    Hybrid gene TEL/AML1 defines subgroup of children with better prognosis and due to its high frequency provides us with a very useful tool for MRD detection.. 