The tyrosine kinase inhibitor imatinib inhibits the activity of the bcr/abl fusion protein present in patients with chronic myeloid leukemia. Although in chronic phase patients response to therapy can be monitored by quantitative RT-PCR for bcr/abl mRNA transcripts, in advanced disease (accelerated phase or blast crisis) only few patients respond on a molecular level. We investigated Wilms tumor gene (WT1) and bcr/abl mRNA transcripts in 16 accelerated phase CML patients by quantitative real time PCR. In contrast to the bcr/abl mRNA levels the WT1 mRNA levels were indicative for hematologic relapse (n = 6) versus response (n = 10).