 Patients will be screened after successful standard induction therapy CR or Cru following standard R-CHOP-like therapy with 8 infusions of rituximab plus CHOP-like chemotherapy 4-8 cycles. Patients will be followed until an event occurs as defined in the protocol. To evaluate the clinical efficacy of rituximab maintenance therapy as compared to observation in patients with aggressive B-cell Non-Hodgkins lymphoma or follicular lymphoma grade 3b who have achieved a complete remission after appropriate first-line therapy, measured by event-free survival EFS, 440 patients with DLCBL or follicular NHL grade 3 220 per arm will be recruited. 