The Bcr-Abl fusion protein plays a crucial role in the initiation and maintenance of chronic myelogenous leukemia (CML). However, additional events are necessary for the transition from the chronic phase to the terminal phase of the disease. To identify genes involved in the disease progression, we constructed a subtractive library from enriched K562 cell mRNA. We obtained 1084 cDNA clones. After a specific hybridization of these clones with a cDNA probe from either chronic phase or K562 cells, 43 clones which present a differential hybridization level have been selected. Among them, several clones corresponded to ribosomal protein genes showing an increased transcription level during the blast crisis. We observed variations in the expression of a cellular adhesion molecule, a laminin-binding protein. An increased transcription level of the MAZ gene has been shown in the terminal phase of the disease. This gene encodes a protein that regulates the transcription of myc.