 We report on a series of Spanish patients with acute lymphoblastic leukaemia in whom the t(12;21) [TEL/AML1] translocation could not be identified with two sensitive techniques: reverse transcript-polymerase chain reaction (RT-PCR) and fluorescence in-situ hybridization (FISH).     ///    Low frequency of the TEL/AML1 fusion gene in acute lymphoblastic leukaemia in Spain..     ///    Specific RT-PCR to amplify the TEL/AML1 fusion transcript was negative in all 101 cases.     ///    "Moreover, all 38 paediatric samples were also negative by interphase FISH analysis for the presence of the TEL/AML1 fusion. "