Inclusion Criteria

Inclusion Criteria

- Patients must have a histologically confirmed diagnosis of low-grade non-Hodgkin's
B-cell lymphoma or low-grade lymphoma that has transformed to intermediate-, or
high-grade lymphoma (transformed lymphoma) according to the Working Formulation for
Clinical Usage (IWF A, B, and C).

- Patients must have evidence that their tumor tissue expresses the CD20 antigen.

- Patients must have progressive disease of either low-grade or transformed lymphoma
within one year of completion of the last chemotherapy regimen administered.

- Patients must have been previously treated with at least one chemotherapy regimen
that included an anthracycline or anthracenedione.

- Patients must have a performance status of at least 60% on the Karnofsky Scale and
anticipated survival of at least three months.

- Patients must have an absolute granulocyte count of over 1,500 /mm3 and a platelet
count above 100,000 /mm3 within seven days of study entry. These blood counts must
be sustained without support of hematopoietic cytokines or transfusion of blood
products.

- Patients must have normal renal function (creatinine less than 2.0 mg/dL) and hepatic
function (bilirubin less than 2.0 mg/dL) within seven days of study entry.

- Patients must have bi-dimensionally measurable or evaluable progressive lymphoma
disease (at least a 25% increase in tumor size or new sites of disease when compared
to the last best disease response). Progression must have occurred within 12 months
of the preceding response.

- Patients must be at least 18 years of age.

- Patients must give written informed consent and sign an approved informed consent
form prior to study entry.

Exclusion Criteria

- Patients with more than an average of 25% of the intertrabecular marrow space
involved by lymphoma in bone marrow biopsy specimens as assessed microscopically at
study entry.

- Patients who have received cytotoxic chemotherapy, radiation therapy,
immunosuppressants, or cytokine treatment within FOUR weeks prior to study entry (six
weeks for nitrosourea compounds) or who exhibit persistent clinical evidence of
toxicity. The use of steroids must have been discontinued (except maintenance-dose
steroids) at least one week prior to study entry and patients must then show evidence
of stable or progressive disease.

- Patients with prior hematologic stem cell transplant following high-dose chemotherapy
or chemo/radiotherapy .

- Patients with obstructive hydronephrosis.

- Patients with evidence of active infection requiring intravenous antibiotics at the
time of study entry.

- Patients with New York Heart Association class 3 or 4 heart disease or other serious
illness that would preclude evaluation.

- Patients with prior malignancy other than lymphoma, except for adequately treated
skin cancer, in situ cervical cancer, or other cancer for which patient has been
disease-free for five years.

- Patients with known HIV infection.

- Patients with known brain or leptomeningeal metastases.

- Patients who are pregnant. Patients of child-bearing potential must undergo a
pregnancy test within seven days of study entry. Males and females must agree to use
effective contraception during the study.

- Patients with previous allergic reactions to iodine. This does not include IV
contrast materials.

- Patients who were previously given any monoclonal or polyclonal antibodies of any
foreign species for either diagnostic or therapeutic purposes. This includes
engineered chimeric and humanized antibodies.

- Patients who previously received radioimmunotherapy.

- Patients with progressive disease in a field that has been previously irradiated with
more than 3500 cGy.

- Patients who are on another protocol involving non-approved drugs or biologics.