Summary of major inclusion and exclusion criteria. Other Safety criteria will need to be met.

Inclusion Criteria:

• Histologically confirmed, relapsed or refractory CD20+ follicular B-cell NHL within 12 months of Study Day 1 (without clinical evidence of transformation). NHL must require treatment as determined by an increase in overall tumor size. The presence of B symptoms, and/or the presence of masses which are causing ongoing clinical symptoms.
• Bidimensionally measurable disease meeting the minimum requirement of at least 1 lesion >/= 2.0 cm in a single dimension.
• No lymphoma therapy for 3 weeks prior to Study Day 1.
• Patients must be recovered from all toxicities associated with prior surgery, radiation therapy, chemotherapy, or immunotherapy.
• Signed IRB-approved informed consent.
• Greater than 18 years of age.
• Expected survival >/= 3 months.
• WHO performance status of </= 2.
• Acceptable hematologic status, liver function, renal function, and pulmonary function.
• Female patients who are not pregnant or lactating.
• Men and women of reproductive potential who are following accepted birth control methods.

Exclusion Criteria:

• Patients with impaired bone marrow reserve, which may be indicated by prior myeloablative therapy with autologous bone marrow transplantation (ABMT) or peripheral blood stem cell (PBSC) rescue.
• Prior radioimmunotherapy, including the Zevalin regimen.
• Prior immunotherapy, including Rituxan therapy within 6 months of Study Day 1.
• Rituxan-refractory (no response to most recent Rituxan-containing regimen, or TTP was < 6 months).
• Presence of CNS lymphoma.
• Patients with chronic lymphocytic leukemia (CLL).
• Known history of HIV or AIDS.
• Serious nonmalignant disease or infection
• Major surgery, other than diagnostic surgery, within 4 weeks of Study Day 1.
• Patients who received investigational product within 4 weeks of Study Day 1 or patients who may experience long-term toxicity from a previous investigational therapy.