--Disease Characteristics-- Acquired severe aplastic anemia or paroxysmal nocturnal hemoglobinuria Not a candidate for allogeneic bone marrow transplantation Must meet one of the following criteria: - Severe aplastic anemia Less than 25% bone marrow cellularity and depression in two of three blood counts (reticulocytes less than 40,000/mm3, platelet count less than 20,000/mm3 and granulocytes less than 500/mm3) - Life-threatening paroxysmal nocturnal hemoglobinuria Absolute neutrophil count less than 500/mm3, platelet transfusion dependent, or thrombotic disease No Fanconi anemia No abnormal cytogenetics --Patient Characteristics-- Renal: Creatinine no greater than 2.0 mg/dL Cardiovascular: Cardiac ejection fraction at least 45% Other: Not preterminal or moribund Not pregnant