This is a Phase 1 study evaluating the safety of ABT-263 administered in combination with either FCR or BR in subjects with relapsed or refractory chronic lymphocytic leukemia.

Inclusion Criteria:

• Must have relapsed or refractory Chronic Lymphocytic Leukemia (CLL), received no more than 5 prior myelosuppressive/chemotherapy regimens and must be a candidate for treatment with either Fludarabine/Cyclophosphamide/Rituximab (FCR) or Bendamustine/Rituximab (BR);
• Subject has an Eastern Cooperative Oncology Group (ECOG) performance score of </=1;
• Must have adequate bone marrow independent of growth factor support (with the exception of subjects with bone marrow heavily infiltrated with underlying disease [80% or more] who may use growth factor support to achieve Absolute Neutrophil Count (ANC) eligibility criteria), per local laboratory reference range at Screening as follows: ANC >/=1000/mcL, Platelets>/= 100,000/mm3 (entry platelet count must be independent of transfusion within 14 days of Screening),Hemoglobin >/= 9.0 g/dL.

Exclusion Criteria:

• Subject has history or is clinically suspicious for cancer-related Central Nervous System disease;
• Has history of severe allergic or anaphylactic reactions to human, humanized, chimeric or murine monoclonal antibodies;
• Has undergone an allogeneic stem cell transplant; Exhibits evidence of other uncontrolled condition(s) including, but not limited to: uncontrolled systemic infection, diagnosis of fever and neutropenia within 1 week prior to study drug administration;
• Has underlying, predisposing condition of bleeding or currently exhibits signs of bleeding; Has a recent history of non-chemotherapy induced thrombocytopenic associated bleeding;
• Currently receiving or requires anticoagulation therapy;
• Has active immune thrombocytopenic purpura (ITP) or a history of being refractory to platelet transfusions (within 1 year prior to 1st dose of study drug);
• Has active peptic ulcer disease or other hemorrhagic esophagitis/gastritis.