PATIENT CHARACTERISTICS: Age: 6 months to 60 years Performance status: No preterminal or moribund patients Life expectancy: No severe limits on life expectancy due to diseases other than leukemia Hematopoietic: See Disease Characteristics Hepatic: Bilirubin no greater than 2.0 mg/dL Transaminases no greater than 3 times normal No severe hepatic disease Renal: Creatinine no greater than 1.5 mg/dL OR Creatinine clearance at least 60 mL/min No severe renal disease No history of severe cystitis with cyclophosphamide Cardiovascular: LVEF at least 50% No symptomatic cardiac disease Pulmonary: FEV1 and FVC at least 75% of normal No severe pulmonary disease Other: HIV negative No severe personality disorder or severe mental illness No condition (such as substance abuse) that would markedly increase the morbidity and mortality of transplantation Criteria of hepatic, renal, cardiac, and pulmonary function and mental illness are used only for initial screening of potential candidates; patients who do not meet these criteria may still be eligible at the discretion of the transplant team