Inclusion Criteria:

1. Patients with age </= 70 years with one of of the following: Acute myeloid leukemia past first remission, in first or subsequent relapse, in second or greater remission or primary induction failure; Myelodysplastic syndromes with intermediate or high risk IPSS score; CML which has progressed to accelerated phase or blast crisis despite imatinib treatment
2. Patients must have an HLA matched related or unrelated donor willing to donate for allogeneic peripheral blood progenitor cell transplantation.
3. Patients must have a haploidentical relative who is predicted to be alloreactive based upon the presence of the relevant KIR genes and incompatibility with the recipient for HLA C and Bw antigens.
4. Zubrod performance status </= 2.
5. Left ventricular ejection fraction >/= 45%. No uncontrolled arrhythmias or uncontrolled symptomatic cardiac disease.
6. No symptomatic pulmonary disease. FEV1, FVC and DLCO >/= 50% of expected, corrected for hemoglobin.
7. Serum creatinine </= 1.8mg%.
8. SGPT </= 200 IU/ml unless related to patients malignancy.
9. Bilirubin </= 1.5 mg/dl (unless Gilbert's syndrome).No evidence of chronic active hepatitis or cirrhosis. If positive hepatitis serology, discuss with Study Chairman and consider liver biopsy.
10. Patient or patient's legal representative, parent(s) or guardian able to sign informed consent.
11. No known allergy to mouse proteins or monoclonal antibodies

Exclusion Criteria:

1. Uncontrolled infection, not responding to appropriate antimicrobial agents after seven days of therapy. The Protocol PI is the final arbiter of eligibility.
2. Pleural/pericardial effusion or ascites estimated to be >1L.
3. HIV-positive.
4. Pregnancy: Positive Beta HCG test in a woman with child bearing potential defined as not post-menopausal for 12 months or no previous surgical sterilization.
5. Known allergy to mouse proteins.
6. Patient has received other systemic chemotherapeutic drugs (including Mylotarg) within 21 days prior to trial enrollment. (Hydroxyurea or low dose ara-c < 20 mg/m2/d is permitted if indicated to control induction refractory disease, and IT chemotherapy is allowed if indicated as maintenance treatment for previously diagnosed LMD, that has been in remission for at least 3 months prior to enrollment on this study).