A 47-year-old woman was admitted to the hospital on March 13, 1998, because of general malaise and fever. It was determined that she had chronic myelogenous leukemia (CML) in myeloid blast crisis. Hydroxyurea was started initially, and the blasts completely disappeared from peripheral blood on day 9 of therapy. Interferon (IFN)-alpha was subsequently started, but lymphoblasts newly appeared on day 13 of administration. Treatment with adriamycin, vincristine, and prednisolone (AdVP) was immediately started, which rapidly reduced the lymphoblasts. However, the myeloblasts again began to gradually increase. Subsequent examinations showed the combined presence of myeloblasts and lymphoblasts in the marrow and peripheral blood. The ratio between myeloblasts and lymphoblasts depended on the treatment (IFN-alpha or AdVP). The patient died from respiratory failure on November 16, 1998. This patient may have had an underlying bipotential blastic clone that evolved differently in response to IFN-alpha or AdVP. In some CML patients, IFN-alpha may induce lymphoid blast crisis.