|Exclusion Criteria:||1) Uncontrolled intercurrent illness including, but not limited to, symptomatic congestive heart failure, unstable angina pectoris, or cardiac arrhythmia.|
2) Active infection not adequately responding to appropriate antibiotics (i.e. ongoing temperatures of >/= 38 degree Celsius).
3) Total bilirubin >/= 1.5 mg/dL and not related to hemolysis or Gilbert's disease. Patients with total bilirubin >/= 1.5 mg/dL to 3 mg/dL are eligible if at least 75% of the bilirubin is indirect.
4) Alanine transaminase (ALT/SGPT) or aspartate transaminase (AST/SGOT) >/= 2.5 x the upper limit of normal.
5) Serum creatinine > 1.5 mg/dL.
6) Female patients who are pregnant or lactating.
7) Patients with reproductive potential who are unwilling to following contraception requirements (including condom use for males with sexual partners, and for females: prescription oral contraceptives [birth control pills], contraceptive injections, intrauterine devices [IUD], double-barrier method [spermicidal jelly or foam with condoms or diaphragm], contraceptive patch, or surgical sterilization) throughout the study.
8) Female patients with reproductive potential who do not have a negative urine or blood beta-human chorionic gonadotropin (beta HCG) pregnancy test at screening.
9) Patients receiving any other concurrent investigational agent or chemotherapy, radiotherapy, or immunotherapy.
10) No prior treatment with cytarabine or clofarabine. Prior hydroxyurea for control of leukocytosis or use of hematopoietic growth factors (eg, G-CSF, GM-CSF, procrit, aranesp, thrombopoietins) is allowed at any time prior to or during study if considered to be in the best interest of the patient.
11) Psychiatric illness or social situation that would limit the patient's ability to comply with study requirements.