Patients with aplastic anemia, myelodysplasia, and other marrow failure syndromes have a variety of immunologic abnormalities including lymphocyte phenotypic and lymphokine production dysregulation. Because of their low blood counts, it has been difficult to obtain sufficient peripheral blood mononuclear cells for research studies. Patients agreeing to this protocol will be lymphapheresed the equivalent of one or two units of cells (approximately 1-2 x 10(8) cells), which will be used for research purposes.