Inclusion Criteria:

- Females of child bearing potential must agree to abstain from sexual activity or to
use a medically approved contraceptive measure/regimen during and for 3 months after
the treatment period or be surgically sterile. Males must agree to abstain from
sexual activity or agree to utilize a medically approved contraception method during
treatment and for 3 months after the treatment period or be surgically sterile.

- Diagnosis of CLL or SLL, relapsed from at least one prior therapy.

- CLL/SLL cells expressing CD20 documented during screening.

- Eastern Cooperative Oncology Group (ECOG) performance status of ≤2.

- Life expectancy of at least 12 weeks.

- Serum creatinine ≤2.0 mg/dL.

- Total bilirubin ≤2.0 mg/dL.

- ALT (alanine aminotransferase) and AST (aspartate aminotransaminase) ≤2 times the
upper limit of normal (ULN); for patients with liver involvement of CLL/SLL disease,
this limit is increased to ≤5 times the ULN.

- At the time of enrollment, patients must be >4 weeks since major surgery,
radiotherapy, chemotherapy (>6 weeks for some chemotherapies), immunotherapy,
biotherapy/targeted or investigational therapies and recovered from the toxicity of
prior treatment to ≤ grade 1.

Exclusion Criteria:

- White Blood Cells (WBC) >250 x 10^9 cells/L.

- Disease refractory to rituximab therapy- defined as a failure to respond to prior
rituximab-containing regimen.

- Women who are breastfeeding.

- Active viral hepatitis.

- Active infection or treatment with antimicrobial or antiviral therapy within 1 week
of enrollment with the exception of prophylactic therapy.

- History of prior allergic reaction to plerixafor or rituximab.

- Significant lung disease.

- Serious cardiac disease such as a history of sustained ventricular arrhythmia,
uncontrolled and serious congestive heart failure (CHF), angina, acute coronary
syndrome, or myocardial infarction within 6 months of enrollment or other significant
medical or psychosocial conditions that warrants exclusion.