The present invention relates to a method of treating chronic myeloid leukemia (CML) in a human patient population. More specifically, the method comprises the steps of (a) determining the OCT-1 Activity in pre-therapy blood of a warm-blooded animal suffering from CML, and (b) administering a daily dose between about 500 and 1200 mg of Imatinib mesylate to the warm-blooded animal suffering from CML showing an OCT-1 Activity below about 6.0 to 10.0 ng/200,000 cells, especially about 8.0 to 8.5 ng/200,000 cells.
