We experienced 2 cases of pulmonary fibrosis, so called “busulfan lung(BL)”, the serious and often fatal complication of busulfan therapy, diagnosed by open lung biopsy in essential thrombocythemia and chronic myelogenous leukemia. Total dose and duration of busulfan administered were 1,100㎎, 28 months and 1,860㎎, 43 months, respectively.
The patients complained of fever and dry cough and diffuse pulmonary infiltration was seen on chest X-ray. The survival duration was 10 weeks and 4 weeks after the
confimation of BL, respectively.
It is stressed that the physicians should keep in mind on the possibility of BL during busulfan therapy and that the early diagnosis of BL might be of benefit.

Keywords: Pulmonary fibrosis, Busulfan lung, Essential thrombocythemia, Chronic myelogenous leukemia