Tyrosine kinase inhibitors have profoundly modified the treatment and prognosis of chronic myeloid leukemia (CML) and Ph(+) acute lymphoblastic leukemia (ALL). A rapid and accurate detection of the bcr-abl fusion protein is paramount today for an optimal management of Ph(+) ALL. We have utilized a recently described and commercialized immunoassay that identifies qualitatively the presence of the bcr-abl protein in leukemic cell lysates. The bcr-abl fusion protein is captured and detected by a cytometric bead assay and analyzed by flow cytometry. The assay was applied to 101 primary patient samples - 94 acute leukemias and 7 CML blast crisis - and the results of the immunoassay were concordant with those obtained by conventional molecular techniques. The method proved reliable, reproducible, of simple execution and it was successfully completed within 4 hours. This flow cytometric immunoassay has important implications towards an optimization of the management of Ph(+) ALL patients worldwide.