Advanced follicular lymphoma is incurable with conventional chemotherapy and radiotherapy. The Southwest Oncology Group (SWOG) conducted a phase 2 trial (S9911) of a novel regimen consisting of 6 cycles of CHOP (cyclophosphamide, doxorubicin, vincristine, and prednisone) chemotherapy followed 4 to 8 weeks later by tositumomab/iodine I 131 tositumomab (anti-CD20 antibody) in 90 eligible patients with previously untreated, advanced stage follicular lymphoma. Treatment was well tolerated. Reversible myelosuppression was the main adverse event and was more severe during CHOP chemotherapy than following radioimmunotherapy. The overall response rate to the entire treatment regimen was 90%, including 67% complete remissions (CRs plus unconfirmed CRs [CRu's]) and 23% partial remissions (PRs). Twenty-seven (57%) of the 47 fully evaluable patients who achieved less than a CR with CHOP improved their remission status after tositumomab/iodine I 131 tositumomab. With a median follow-up of 2.3 years, the 2-year progression-free survival (PFS) was estimated to be 81%, with a 2-year overall survival of 97%. This study has established the feasibility, tolerability, and efficacy of this regimen for patients with advanced follicular lymphoma. This novel treatment appears promising compared with the SWOG's historical experience using CHOP alone and is currently being compared with CHOP plus rituximab in a randomized phase 3 trial (S0016).