Inclusion Criteria

DISEASE CHARACTERISTICS:

- Histologically or cytologically confirmed B-cell lymphoma

- Relapsed disease

- CD20-positive disease

- Must have had bone marrow aspiration and biopsy (uni- or bilateral) within the past
42 days and chest CT and CT of the abdomen and pelvis within the past 28 days

- Documented bidimensionally measurable disease within the past 28 days

- Patients with non-measurable disease in addition to measurable disease must have
all non-measurable disease assessed within 42 days prior to registration

PATIENT CHARACTERISTICS:

- Eastern Cooperative Oncology Group(ECOG) performance status 0-2

- Leukocyte count ≥ 3,000/μL

- Absolute neutrophil count ≥ 1,500/μL

- Platelet count ≥ 75,000/μL

- Total bilirubin ≤ 2 times upper limit of normal (ULN)

- AST and ALT ≤ 2.5 times ULN

- Alkaline phosphatase ≤ 2.5 times ULN

- Creatinine ≤ 2.0 mg/dL OR creatinine clearance ≥ 30 mL/min

- Not pregnant or nursing

- Negative pregnancy test

- Fertile patients must use effective contraception during and for at least 6 months
after completion of study therapy

- No known AIDS or HIV-associated complex

- No active hepatitis B infection

- No other severe concurrent disease, history of serious organ dysfunction, or disease
involving the heart, kidney, liver, or other organ system that may place the patient
at undue risk to undergo treatment

- No uncontrolled systemic fungal, bacterial, viral, or other infection, defined as
ongoing signs/symptoms related to the infection and without improvement, despite
appropriate antibiotics or other treatment

- No history of intolerance or allergic reactions to clofarabine or rituximab

- No significant concurrent disease, illness, or psychiatric disorder that would
compromise the patient's safety or compliance, interfere with consent, study
participation, follow up, or interpretation of study results

- No concurrent active GI disease that may impair absorption of oral clofarabine

PRIOR CONCURRENT THERAPY:

- Recovered from all previous therapies

- No prior gastrointestinal (GI) surgery that may impair absorption of oral clofarabine

- More than 2 weeks since prior and no concurrent anticancer therapy, except for
hydroxyurea

- More than 4 weeks since prior radioimmunotherapy

- More than 1 month since prior investigational agents

- No concurrent cytotoxic therapy or investigational therapy

- No other concurrent investigational or commercial agents or therapies administered
with the intent to treat the patient's malignancy

- No concurrent alternative medications (e.g., herbal or botanical for anticancer
purposes)

- No other concurrent chemotherapy or immunotherapy

- No concurrent radiotherapy

- No concurrent colony stimulating factors (phase I portion of the study)