The title of this study is interindividual genetic variability as a determinant of chemotherapy toxicity and response in pediatric oncology/bone marrow transplantation patients. We will collect blood from pediatric oncology/bone marrow transplantation patients who are going to receive chemotherapy in order to assess several defined genetic polymorphisms that may be involved in chemotherapy toxicity and response. The polymorphisms will be assessed on normal mononuclear cells by a combination of techniques. We will determine whether these polymorphisms occur in pediatric oncology/bone marrow transplantation patients and their correlation with different clinical features during and following therapy including toxicity and response. The presence or absence of polymorphisms will be correlated with patient outcome and tumor recurrence.