Chronic myelogenous leukemia (CML) is a myeloproliferative disorder triggered by a chromosomally induced mutation in a pluripotent stem cell. Its progressive clinical course consists of a chronic or benign phase, which terminates in blast crisis. Historically, treatment has been limited: conventional chemotherapy yields a median survival of approximately 36 to 42 months, and bone marrow transplantation, while achieving success in more than half of patients treated, is limited to younger patients with HLA-matched siblings. Treatment with interferon alfa in CML was initiated in 1981. The first studies were performed using partially pure interferon alfa; these studies were followed by treatment regimens employing interferon alfa-2a.