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. Conventional therapeutic options include interferon-based regimens and stem-cell transplantation, with stem-cell transplantation being the only curative therapy. Through rational drug development, STI571, a bcr-abl tyrosine kinase inhibitor, has emerged as a paradigm for gene product-targeted therapy, offering new hope for expanded treatment options for patients with CML.