1. Patients with a diagnosis of advanced stage indolent non-Hodgkin's lymphoma expressing the CD20 surface antigen (as measured by immunohistochemistry or flow cytometry on peripheral blood, marrow, or tumor tissue). Specific histologic subtypes which are eligible include follicular small cleaved cell (follicular grade 1) and follicular mixed small cleaved and large cell (follicular grade 2) lymphoma, and small lymphocytic lymphoma. Patients with indolent follicular lymphoma (follicular grades 1 and with areas of diffuse histology and patients with diffuse follicle center cell lymphoma are eligible as long as the diffuse areas are not felt to represent areas of transformation to diffuse large B-cell lymphoma.