The purpose of this study is to determine whether anti-CD80 monoclonal antibody (IDEC-114) is effective in the treatment of follicular B-cell non-Hodgkin's lymphoma. This drug has never been studied in patients with lymphoma, however, it has been studied in psoriasis patients at various dose levels and schedules.

Inclusion Criteria:

• Histologically confirmed follicular lymphoma that has relapsed or has failed primary therapy
• Progressive disease requiring further treatment
• Bidimensionally measurable disease
• Acceptable hematologic status
• Prestudy WHO performance status of 0, 1, or 2
• Expected survival of >/= 3 months
• Patients with reproductive potential must follow accepted birth control methods during treatment and for 3 months after completion of treatment
• Female patients must not be pregnant or lactating
• Recovered fully from any significant toxicity associated with prior surgery, radiation treatments, chemotherapy, biological therapy, ABMT, or investigational drugs

Exclusion Criteria:

• Cancer radiotherapy, biological therapy, or chemotherapy within 3 weeks of first scheduled treatment (6 weeks if nitrosourea or mitomycin-C)
• Prednisone or other immunosuppressive therapy within 3 weeks of first scheduled treatment
• Prior antibody therapy for lymphoma (including radioimmunotherapy) within 6 months prior to first scheduled treatment
• Previous exposure to IDEC-114 or any anti-CD80 antibody
• ABMT within 6 months prior to first scheduled treatment
• Abnormal liver function
• Abnormal renal function
• Presence of chronic lymphocytic leukemia (CLL)
• Presence of CNS lymphoma
• Presence of HIV infection or AIDS
• Prior diagnosis of aggressive non-Hodgkin's lymphoma or mantle-cell lymphoma
• Another primary malignancy (other than squamous cell and basal cell carcinoma of the skin, in situ carcinoma of the cervix, or treated prostate cancer with a stable PSA) for which the patient has not been disease-free for at least 3 years
• Serious nonmalignant disease which would compromise protocol objectives in the opinion of the investigator and/or the sponsor
• New York Heart Association Class III or IV cardiac disease or myocardial infarction within 6 months prior to first scheduled treatment
• Major surgery, other than diagnostic surgery, within 4 weeks prior to first scheduled treatment
• Pleural invasion and/or effusion with positive cytology for lymphoma
• Peritoneal invasion and/or ascites with positive cytology for lymphoma