In ~1% of the CML patients the bone marrow cells appear to be Ph negative by G-banding, although the BCR/ABL1 fusion gene can be identified by molecular means and located by fluorescence in situ hybridisation (FISH) on chromosome 22q11, 9q34 or even a third chromosome. The gene discussed is ABL1; the disease is chronic myelogenous leukemia, BCR-ABL1 positive.