We report on a Ph+ chronic myelocytic leukemia (CML) case, cytogenetically characterized by the occurrence of a second Philadelphia (Ph) chromosome in lymphoid blast crisis of T cell lineage. In situ hybridization analyses showed a deletion of translocated c-abl sequences, present on the Ph during chronic state, from both Ph in acute state. Moreover, Southern blot analyses of blastic cells exhibited a rearrangement within bcr, but a deletion of 5' bcr sequences, and Northern blots failed to detect the hybrid 8.5 kb bcr/c-abl transcript usually observed in Ph+ CML.