Phase III Randomized Study of Cyclophosphamide With or Without Antithymocyte Globulin Before Bone Marrow Transplantation in Patients With Aplastic Anemia

PROTOCOL ENTRY CRITERIA: --Disease Characteristics-- Severe aplastic anemia with the following criteria: Hypocellular bone marrow with cellularity less than 20% At least 2 of the following hematologic abnormalities: * Neutrophil count no greater than 500/mm3 * Platelet count no greater than 20,000/mm3 * Reticulocyte count no greater than 50,000/mm3 HLA-identical sibling donor available No clonal cytogenetic abnormalities, paroxysmal nocturnal hemoglobinuria, or myelodysplastic syndrome within 3 months of diagnosis of aplastic anemia No congenital or constitutional aplastic anemia or Fanconi anemia --Patient Characteristics-- Hepatic: Bilirubin less than 3 times upper limit of normal (ULN) Renal: Creatinine less than 2 times ULN Cardiovascular: Normal cardiac function Other: * No uncontrolled infection * No severe concurrent disease * HIV negative * Fertile patients must use effective contraception