Phase II Study Evaluating Busulfan and Fludarabine as Preparative Therapy in Adults With Hematopoietic Disorders Undergoing MUD SCT

Inclusion Criteria: * No fully or single-antigen mismatched sibling donor is available to donate stem cells. * Age \>15 and \<61 * ECOG PS \< or equal to 2 * Adequate renal function with serum creatinine \<2.0 mg/dl * Pulmonary diffusing capacity \>40% of predicted * Cardiac ejection fraction \>40% as measured by radionuclide wall motion study or echocardiography * No active liver disease. Total bilirubin must be \< or equal to 2.0 mg/dl. Alkaline phosphatase and AST must be less than three times the upper limit of normal. Patients with hepatitis C and active hepatitis B are eligible only if a liver biopsy is performed and there is \< or equal to grade 2 inflammation. Patients wtih a history of HBV infection should be tested for HBeAg, antiHBe and HBV DNA (quantitative). Patients with active HBV viral replication should receive anti-viral therapy. * Negative serology for the human immunodeficiency virus (HIV) * Available HLA-matched donor (see HLA compatibility requirements below) * Signed informed consent from the recipient Exclusion Criteria: * Ongoing active infection * Pregnancy and/or nursing * Active, uncontrolled CNS leukemia * Opinion of BMT Committee that autologous or mini-allogeneic transplant would be the preferable form of treatment * Receipt of any chemotherapy within 3 weeks of study entry except for hydroxyurea or imatinib mesylate. Use of interferon within 3 months of starting therapy.