A Randomized Study of Iodine-131 Anti-b1 Antibody Versus Anti-b1 Antibody in Chemotherapy-relapsed/Refractory Low-grade or Transformed Low-grade Non-Hodgkin's Lymphoma (NHL)

Subjects will be randomized to receive tositumomab and iodine-131 tositumomab (Arm A) or unlabeled tositumomab (Arm B). Subjects randomized to receive unlabeled tositumomab may crossover and receive radiolabeled Iodine-131 tositumomab following progression of their lymphoma. Response in both arms will be assessed at 7 weeks, 13 weeks, and then at 3-monthly intervals for up to 2 years.