A patient with polycythemia vera received a moderate dose (480 mg) of busulfan intermittently over a 6 year period and later developed Hodgkin's disease. Following split-course upper mantle, chest irradiation, he developed rapidly progressive, fatal pneumonia and bone marrow hypoplasia. It is postulated that the hyperacute organ failures (lung and bone marrow) resulted from augmentation of subclinical busulfan-induced damage of these organs by additive radiation effect. It is recommended that in patients who have had antineoplastic chemotherapy, major radiotherapy to the cervicothoracic region be accompanied by careful monitoring of respiratory and hematopoietic function, both before and during radiotherapy.