Chronic myelogenous leukemia (CML) is a clonal hematopoietic stem cell disorder characterized by the (9:22) translocation and resultant production of the constitutively activated bcr-abl tyrosine kinase. Characterized clinically by marked myeloid proliferation, it invariably terminates in an acute leukemia. Interferon-based regimens and stem cell transplantations are the standard therapeutic options, with stem cell transplantation being the only curative therapy. As therapy for CML improves, molecular methods of monitoring response will become integrated in patient treatment. Through rational drug development, STI571, a bcr-abl tyrosine kinase inhibitor, has emerged as targeted therapy that offers new hope for expanded treatment options for patients with CML.