 Deletions from the derivative chromosome 9, der(9), of the translocation, t(9;22)(q34;q11), at the site of the ABL/BCR fusion gene, have been demonstrated by fluorescence in situ hybridisation (FISH), in both Philadelphia chromosome (Ph)-positive chronic myeloid leukaemia (CML) and acute lymphoblastic leukaemia (ALL).     ///    This study presents the findings of dual fusion FISH used to detect such deletions in a series of 27 BCR/ ABL-positive childhood ALL patients. 