RATIONALE: Radiolabeled monoclonal antibodies can locate tumor cells and deliver radiation to them without harming normal cells.

PURPOSE: Phase II trial to study the effectiveness of rituximab and ibritumomab tiuxetan in treating patients who have relapsed or refractory non-Hodgkin's lymphoma.

OBJECTIVES: I. Determine the efficacy and safety of rituximab and ibritumomab tiuxetan radioimmunotherapy in patients with refractory or relapsed, low-grade, follicular, or transformed B-cell non-Hodgkin's lymphoma.

OUTLINE: This is a multicenter study. Patients receive rituximab IV on days 1 and 8 immediately followed by IDEC-In2B8 IV over 10 minutes on day 1. Patients also receive ibritumomab tiuxetan IV over 10 minutes on day 8. Patients are followed every 3 months for 2 years and then every 6 months for 2 years.

PROJECTED ACCRUAL: Approximately 400 patients will be accrued for this study.

DISEASE CHARACTERISTICS: Histologically proven relapsed or refractory, low-grade, follicular, or transformed B-cell non-Hodgkin's lymphoma (NHL) Prior rituximab allowed if no response achieved CD20-positive B-cells in lymph nodes or bone marrow required for small lymphocytic or transformed NHL Less than 25% of bone marrow cellularity in lymphoma cells No impaired bone marrow reserve, as indicated by one or more of the following: Prior myeloablative therapy with bone marrow transplantation or peripheral blood stem cell rescue Platelet count less than 100,000/mm3 Hypocellular bone marrow (no more than 15% cellularity) Marked reduction in bone marrow precursors of one or more cell lines (granulocytic, megakaryocytic, or erythroid) History of failed stem cell collection Not eligible for any active ibritumomab tiuxetan investigative protocols No CNS lymphoma, AIDS-related lymphoma, or chronic lymphocytic leukemia No pleural effusion A new classification scheme for adult non-Hodgkin's lymphoma has been adopted by PDQ. The terminology of "indolent" or "aggressive" lymphoma will replace the former terminology of "low", "intermediate", or "high" grade lymphoma. However, this protocol uses the former terminology.

PATIENT CHARACTERISTICS: Age: 18 and over Performance status: WHO 0-2 Life expectancy: At least 3 months Hematopoietic: See Disease Characteristics Absolute neutrophil count at least 1,500/mm3 Lymphocyte count no greater than 5,000/mm3 (for small lymphocytic lymphoma) Platelet count at least 150,000/mm3 Hepatic: Bilirubin no greater than 2.0 mg/dL Renal: Creatinine no greater than 2.0 mg/dL Other: Not pregnant or nursing Negative pregnancy test Fertile patients must use effective contraception during and for 6 months after study HIV negative No serious nonmalignant disease or infection that would preclude study No antimurine antibody reactivity

PRIOR CONCURRENT THERAPY: Biologic therapy: See Disease Characteristics At least 6 weeks since prior rituximab At least 3 weeks since prior immunotherapy and recovered No prior radioimmunotherapy At least 2 weeks since prior filgrastim (G-CSF) or sargramostim (GM-CSF) Chemotherapy: See Disease Characteristics At least 3 weeks since prior chemotherapy (6 weeks for nitrosourea or mitomycin) and recovered Endocrine therapy: Not specified Radiotherapy: See Biologic therapy At least 3 weeks since prior radiotherapy and recovered No prior external beam radiotherapy to more than 25% of active bone marrow (involved field or regional) Surgery: At least 4 weeks since prior major surgery (other than diagnostic) and recovered Other: At least 3 weeks since prior anticancer therapy and recovered At least 8 weeks since prior phase II drugs and recovered No other concurrent myelosuppressive antineoplastic agents No other concurrent antineoplastic therapy