Recent advances in the field of immunotherapy have proved to benefit patients with relapsed or refractory B-cell NHL. In 1997, rituximab became the first FDA-approved monoclonal antibody (mAb) for the treatment of cancer. Rituximab, a chimeric IgG1 kappa monoclonal antibody, specifically recognizes and binds to the CD20 antigen found on the cell surface of most normal B-cells and malignant B-cell lymphomas. Rituximab binds human complement and lyses B-cell lines through complement dependent cytotoxicity and antibody dependent cellular toxicity. A multi-center Phase II trial of 166 patients with relapsed indolent B-cell lymphoma treated with rituximab found an overall response in 50% of patients with 6% having a complete response and 44% having a partial response. Time to progression was a median of 13 months in patients who responded.