Prolonged myelosuppression, severe granulocytopenia, thrombocytopenia, anemia, or any combination may develop. High-dose oral busulfan may cause seizure; patients w/ history of seizure disorder or head trauma or who are receiving other potentially epileptogenic drugs. High AUC values may be associated w/ increased risk of developing HVOD. Cardiac tamponade in ped patients w/ thalassemia who received high doses. Bronchopulmonary dysplasia w/ pulmonary fibrosis. Cytologic abnormalities characterized by giant, hyperchromatic nuclei in lymph nodes, pancreas, thyroid, adrenal glands, liver, lungs & bone marrow. Monitor complete blood counts, including WBC differentials & quantitative platelet counts daily during treatment & until engraftment is demonstrated. Monitor serum transaminases, alkaline phosphatase & bilirubin daily. Pregnancy & lactation. Childn.