Non-Hodgkin's lymphoma (NHL) is composed of a group of lymphoid malignancies that has been increasing in incidence at an annual rate of 4% to 7% over the last 20 years in both the United States and Europe. The reasons for this rise in incidence in NHL are not yet defined but most likely involve environmental exposures. Low-grade and follicular lymphomas account for approximately 40% of the incidences of NHL in the United States. While patients with intermediate- and high-grade lymphomas are potentially curable with combination chemotherapy, low-grade and follicular lymphomas are still considered to be essentially incurable with standard therapy. Although low-grade lymphomas characteristically respond well to treatment with chemotherapeutic agents, the disease typically follows a course of recurrent relapse and progressively shorter remissions, and ultimately death from lymphoma. Median survival for patients with low-grade lymphoma is 6.2 years from diagnosis and just 5 years from time of first relapse. Therefore, novel therapeutic strategies are urgently needed for these patients. One approach to the development of innovative strategies for treatment of NHL has been the generation of monoclonal antibodies to specific B-cell antigens expressed on NHL cells.