Fig. 5 shows that exposure to 1.0 μmol/l imatinib for 48 h did not reduce the BCR-ABL protein levels, but did reduce the PTK activity in the CD34+ cells from patients with CML in the megakaryocytic and myeloid crisis phases. However, the decline in PTK activity was not notably different between the CD34+ cells from patients with CML in the megakaryocytic crisis phase and those from patients with CML in the myeloid crisis phase. This evidence concerns the gene PTK2B and chronic myelogenous leukemia, BCR-ABL1 positive.