Philadelphia chromosome positive chronic myeloid leukemia (Ph+ CML), in advanced stage of disease, is resistant to standard chemotherapy. Imatinib was found to be effective in these patients. This paper shows our preliminary results. Imatinib mesylate was given to 15 patients during a 9-month period. Nine of them were in accelerated phase and 6 in blastic crisis of Ph+ CML. Patients were evaluated for hematologic and cytogenetic responses. Imatinib mesylate induced complete haematologic response in 12 patients (80% and cytogenetic response in 8 patients (53%). Six patients (40%) had a major cytogenetic response. After a 9-month follow up Ph+ CML progressed in 9 patients (60%) and 4 of them died. The most frequent adverse effects were edema, nausea, neutropenia and thrombocytopenia. Imatinib mesylate has a substantial, but short term activity in the accelerated phase and blastic crisis of the Ph+ CML.