A 29-year-old man had received a diagnosis of chronic myelogenous leukemia (CML) 6 years before pressentation. He had not undergone bone marrow transplantation because of the lack of an adequate donor. He entered an accelerated phase in 1994 and was treated with oral hydroxyurea and 6-mercaptopurine. The patient developed a dry cough and mild fever in December 2000 and was treated for pneumonia in a local hospital. He was sent to the emergency department of our hospital in April 2001 with a 1-month history of fever, chills, and exertional dyspnea. He also had complained of malaise and a dry cough in the preceding 3 months. There was no history of recent travel, and he was taking no drugs other than hydroxyurea and 6-mercaptopurine.