Inclusion Criteria:

- Have a diagnosis of Acute Myelogenous Leukemia (AML) according to World Health
Organization (WHO) classification

- Relapsed after receiving up to 2 prior induction regimens (i.e. first or second
relapse)or are refractory to not more than one prior combination chemotherapy
induction regimen

- Be ≥ 55 years of age

- Have an Eastern Cooperative Oncology Group (ECOG) score of 0-2

- Be able to comply with study procedures and follow-up examinations

- Be nonfertile or agree to use birth control during the study through the end of
treatment visit and for at least 90 days after the last dose of study drug

- Have adequate liver and renal function as indicated by certain laboratory values

Exclusion Criteria:

- Received previous treatment with clofarabine

- Received bolus, intermediate or high-dose cytarabine as induction therapy unless
certain remission criteria are met

- Have received a hematopoietic stem cell transplant (HSCT) within the previous 3
months

- Have moderate or severe graft versus host disease (GVHD), whether acute or chronic

- Are receiving any other chemotherapy or investigational therapy. Patients must have
been off prior AML therapy for at least 2-6 weeks prior to entering study.

- Have a psychiatric disorder that would interfere with consent, study participation,
or follow-up

- Have an active, uncontrolled infection

- Have any other severe concurrent disease, or have a history of serious organ
dysfunction or disease involving the heart, kidney, liver, or other organ system

- Have been diagnosed with another malignancy, unless disease-free for at least 5
years; patients with treated nonmelanoma 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 surgically removed.

- Have clinical evidence suggestive of central nervous system (CNS) involvement with
leukemia unless lumbar puncture confirms absence of leukemic blasts in the
cerebrospinal fluid(CSF)

- Known HIV positivity

- Are pregnant or lactating