Imatinib mesylate (Gleevec, Novartis Basel, Switzerland; STI571), a Kit, Abl and PDGFR inhibitor, induces apoptosis of the Ph1 CML progenitors by suppressing the ability of BCR/ABL to phosphorylate substrates through competitive inhibition at the BCR/ABL ATP binding site (Druker et al, 1996). This evidence concerns the gene ABL1 and chronic myelogenous leukemia, BCR-ABL1 positive.