Inclusion Criteria:

• Age ≥18 years
• Histologically confirmed marginal zone lymphoma or follicular lymphoma (grade 1, 2 or 3a)
• Documented relapsed, refractory or progressive disease after treatment with systemic therapy
• Rituximab naïve or rituximab sensitive
• Investigator considers rituximab monotherapy appropriate
• Bi-dimensionally measurable disease
• Eastern Cooperative Oncology Group (ECOG) Performance status ≤ 2
• Adequate bone marrow function
• Willingness to follow pregnancy precautions

Exclusion Criteria:

• Histology other than follicular or marginal zone lymphoma or clinical evidence of transformation or Grade 3b follicular lymphoma
• Subjects taking corticosteroids during the last week, unless administered at a dose equivalent to < 20 mg/day prednisone
• Systemic anti-lymphoma therapy within 28 days or use of antibody agents within 8 weeks use of radioimmunotherapy within 6 months
• Known seropositive for or active viral infection with hepatitis B virus (HBV), hepatitis C virus (HCV), human immunodeficiency virus (HIV)
• Known sensitivity or allergy to murine products
• Presence or history of central nervous system involvement by lymphoma.
• Subjects who are at a risk for a thromboembolic event and are not willing to take prophylaxis for it.
• Any condition that places the subject at unacceptable risk if he/she were to participate in the study or that confounds the ability to interpret data from the study.