To investigate the incidence of TEL/AML1 fusion and TEL deletion, bone marrow specimens from 77 Korean children with newly diagnosed acute leukemia were analyzed by FISH.     ///    We applied extra-signal FISH to discriminate a true TEL/AML1 fusion from a false-positive fusion signal.     ///    " TEL/AML1 fusion in acute leukemia results from cryptic translocation of chromosome 12 and 21, the presence of which suggests a favorable prognosis. "    ///    "The incidence of TEL/AML1 fusion in B-lineage ALL is approximately 25%, but the incidence in Korea has not yet been reported. "    ///    The frequency of patients with TEL/AML1 fusion was 13.3% (4 cases) among 30 B-lineage ALL and 9.5% among 42 ALL.     ///    Low incidence of TEL/AML1 fusion and TEL deletion in Korean childhood acute leukemia by extra-signal fluorescence in situ hybridization..     ///    TEL/AML1 fusion was not found in any samples from patients with T-lineage ALL or AML.     ///    "To determine the cut-off value of the TEL/AML1 fusion signal, 20 normal bone marrow specimens and 28 normal peripheral blood specimens were also analyzed. "    ///    "The incidences of TEL/AML1 fusion and TEL deletion in Korean children with acute leukemia appear to be lower than those in other countries, suggesting a racial difference.. "