MDS of RA & RAEB sub-types.
No current treatment and off other treatments for at least two weeks.
ECOG performance status less than or equal to 2.
No MDS of FAB sub-group' refractory anemia with ring sideroblasts' (RARS).
No transforming to acute leukemia (FAB sub-group RAEB-Tie.; greater than 20% blasts in marrow aspirate).
No hypoplastic marrow without one major or two minor criteria as outlined in table 3 of the appendix.
No one being treatment with growth factors or cyclosporine within four weeks prior to entry to protocol.
No previous treatment with ATG.
No ECOG performance status of greater than 2.
No active uncontrolled infection.
No women which current pregnancy, or unwilling to take oral contraceptives if of childbearing potential.
No patients for whom bone marrow transplant is indicated as primary therapy.
No one age less than 18 years.
Must be able to give informed consent.
No HIV positive patients.
No active malignant disease (excluding basal cell carcinoma).
No one with serum creatine greater than 2mg/dl.
No patients who are moribund or patients with concurrent hepatic, renal, cardiac, metabolic, or any disease of such severity that death within 7-10 days is likely.