Fifty ALL children (40 De Novo, 10 Relapsed) were analyzed for the presence of t (12; 21) using two techniques: Fluorescence in situ hybridization (FISH) and polymerase chain reaction (PCR) for detection of the fusion gene (TEL-AML1) 16% of all cases were positive (17.5% in De Novo cases, 10% in relapsed cases). Although not achieving statistical significance, favorable prognostic parameters (younger age, lower leucocytic count and low blast cell counts in P, B) were consistent with the presence of the TEL-AML1 fusion gene.