The purpose of this study is to provide treatment for patients who have relapsed NHL or refractory NHL, and to determine the effectiveness and safety of the Zevalin and Rituxan regimens or Rituxan therapy alone on your disease.

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 \