A patient with Philadelphia (Ph1)-negative, breakpoint cluster region (bcr)-positive chronic myeloid leukemia (CML) is reported. Pulsed-field gel electrophoretic analysis demonstrated the comigration of both ABL and BCR sequences on the same BssHII and SacII fragment. Moreover, in situ hybridization studies demonstrated that ABL sequences had been moved from band 9q34 to 22q11 and that the additional t(12;12)(q13;p12) was not involved in the ABUBCR related translocation. Nevertheless, a possible role of oncogenes or regulatory sequences activated or inhibited by the additional translocation cannot be excluded.