Non-Hodgkin's lymphomas (NHL) are a heterogeneous group of lymphoid malignancies that represent the 6th leading cause of cancer death and the 2nd fastest growing cancer in the United States. NHLs can be divided into two prognostic groups: aggressive and indolent lymphomas. Aggressive NHLs grow rapidly and present as disseminated disease in 70% of cases, yet can be cured in a significant number of patients with intensive combination chemotherapy regimens. Indolent (low-grade) NHLs are slow growing malignancies with long natural histories that are incurable when disseminated. Early stage low-grade NHL (stage I and II) has the potential for cure with radiotherapy, but only 10-20% of patients with low-grade NHL present with early stage disease. The vast majority of patients with low-grade NHL present with advanced disseminated disease. While indolent B-cell NHLs have initial sensitivity to chemotherapy and radiotherapy, they frequently relapse and become increasingly resistant to therapy with each successive relapse, eventually transforming to aggressive lymphomas in most patients. Fifty percent of patients presenting with advanced indolent NHL die within 5 years of their first relapse. Only modest improvement has been made in the last 25 years in increasing the survival of patients with indolent NHL with current median survival of 7-10 years.