Inclusion Criteria:

          1. Adult patients age 18 years or older, with a pathologically confirmed diagnosis of AML
             [excluding acute promyelocytic leukemia (APL)] according to WHO criteria. AML may be
             de novo, or following a prior hematologic disease and/or therapy-related.

          2. Patients must have relapsed after or be refractory to at least one course of an
             intensive chemotherapy regimen, for example anthracycline/cytarabine ("7+3" or
             daunorubicin and cytarabine liposome). Patients with residual disease on day 13-22 of
             initial induction chemotherapy are eligible, provided the bone marrow cellularity is ≥
             30% AND bone marrow blasts are ≥ 20%. Hypomethylating agents such as azacitidine or
             decitabine are allowed as a prior therapy, but are not considered an intensive
             chemotherapy regimen.

          3. Eastern Cooperative Oncology Group performance status of 0-2.

          4. Any systemic chemotherapy and any radiotherapy must be completed at least 7 days prior
             to initiation of protocol therapy, with the exception of hydroxyurea or
             6-mercaptopurine for cytoreduction.

          5. At least 20% expression of CD33 as determined by flow cytometry or immunohistochemical
             staining.

          6. Adequate renal function, defined as a serum creatinine less than 1.8 mg/dL.

          7. Adequate hepatic function, defined as a direct bilirubin less than 2 times the
             institutional upper limit of normal (ULN) and AST, ALT and Alkaline Phosphatase less
             than 3 times the ULN.

          8. Patients who relapse after allogeneic hematopoietic stem cell transplantation are
             eligible, provided they are at least 60 days from stem cell infusion, do not have >
             grade 1 graft versus host disease, and have been off all immunosuppressive therapy for
             at least 2 weeks.

          9. Female patients of childbearing potential must have a negative pregnancy test and
             agree to use an adequate method of contraception as defined by the protocol. This must
             persist through the treatment period until at least 6 months after the last dose of
             chemotherapy or GO.

         10. Male subjects who are able to father children and are having intercourse with females
             of childbearing potential must also agree to an acceptable method of contraception
             through the treatment period until at least 3 months after the last dose of
             chemotherapy or GO, and must refrain from sperm donation during this period.

         11. Ability to give written informed consent.

        Exclusion Criteria:

          1. Patients with acute promyelocytic leukemia (FAB-M3) or chronic myelogenous leukemia in
             blast phase.

          2. Isolated myeloid sarcoma. Patients must have marrow involvement with AML to enter the
             study.

          3. Patients with known active AML involvement of the central nervous system.

          4. Prior treatment with gemtuzumab ozogamicin or cladribine for AML. Prior treatment with
             cytarabine is permitted.

          5. As patients will be receiving G-CSF prior to chemotherapy, patients presenting with
             symptomatic leukostasis (as judged by the investigator) are excluded. Hydroxyurea,
             6-mercaptopurine and/or leukapheresis for blast count control (see inclusion criterion
             #4) for patients with asymptomatic hyperleukocytosis is permitted before starting
             treatment, but must be stopped for at least 24 hours prior to starting protocol
             treatment.

          6. Active uncontrolled infection. Patients on prophylactic antibacterial, antifungal,
             and/or antiviral agents and patients whose infections are controlled with these agents
             are eligible.

          7. Known active hepatitis B or C or other known active hepatic disorder.

          8. Any history of veno-occlusive disease (VOD)/sinusoidal obstruction syndrome (SOS).

          9. Active concurrent malignancy, unless disease-free for at least 3 years. Subjects with
             treated non-melanoma skin cancer, in situ carcinoma or cervical intraepithelial
             neoplasia, regardless of the disease-free duration, are eligible for this study if
             definitive treatment for the condition has been completed. Patients with
             organ-confined prostate cancer with no evidence of recurrent or progressive disease
             are eligible if hormonal therapy has been initiated or the malignancy has been treated
             surgically or with definitive radiotherapy.

         10. Uncontrolled intercurrent illness including, but not limited to, symptomatic
             congestive heart failure, unstable angina pectoris, cardiac arrhythmia, or psychiatric
             illness/social situations that per investigator's judgment would limit compliance with
             study requirements.