Patients with a type of non-Hodgkin lymphoma, called follicular lymphoma and have not yet had previous systemic treatment, such as chemotherapy or immunotherapy will be invited to participate. This research study is being conducted in order to evaluate the combination of lowdose methotrexate and Iodine I 131 tositumomab (Bexxar) with regards to whether the combination will reduce the occurrence of the HAMA (Human Anti-Mouse Antibody) response. HAMA is an immune reaction against the tositumomab protein. Symptoms arising from HAMA can range from a mild form, like a rash, to a more extreme and possibly life-threatening level. HAMA can also decrease the effectiveness of the treatment, or create a future reaction if a patient is given another treatment containing mouse antibodies. In addition to evaluating the occurrence of HAMA, this research study will also look at the short and long-term effectiveness of this combination in the treatment of lymphoma, as well as its safety.