This study will evaluate the safety and effectiveness of MabThera (rituximab) in patients with active rheumatoid arthritis who are receiving methotrexate, and who have a previous or current inadequate response to one prior anti-TNF therapy. All patients will receive MabThera 1000 mg as an intravenous infusion on days 1 and 15. After the initial study phase of 24 weeks, eligible patients may receive one re-treatment with MabThera. The anticipated time on study treatment is 48 weeks.