Over the past year, new information has been reported on the biology and treatment of chronic myelogenous leukemia (CML). Chronic myelogenous leukemia is characterized by the breakpoint cluster region (BCR-ABL) chimeric gene, the product of which is p210BCR-ABL, a tyrosine kinase that gives hematopoietic cells the characteristics of excessive proliferation, resistance to physiologic apoptotic signals, and resistance to chemotherapy. Recently, investigators have attempted to 1) elucidate the mechanisms by which the BCR-ABL gene and its product initiate and maintain the malignant phenotype, 2) improve the use of the BCR-ABL gene as a diagnostic marker of disease, and 3) inhibit the expression of this gene as a therapeutic maneuver. Other investigators have tried to explain interferon's mechanism of action in the treatment of CML and to improve the safety and applicability of stem cell transplantation (SCT) as a therapy for CML.