Patients with high-risk hematopoietic malignancies that express CD33 (i.e. AML, ALL, CML and MDS) will be included. We will enroll older patients (>55 years old) or medically infirm patients who are unable to tolerate standard allogeneic bone marrow transplant. Patients will be evaluated at 28 days post-transplant for evidence of response. Those with residual disease may be eligible for additional Mylotarg given together with donor lymphocyte infusions. Additional courses of Mylotarg may improve overall survival in this poor prognosis group.