This single arm study will evaluate the safety and efficacy of MabThera in patients with active rheumatoid arthritis who are receiving methotrexate treatment, and who have had an inadequate response to one anti-TNF alpha therapy. All patients will receive MabThera 1000mg i.v. on days 1 and 15, in addition to concomitant methotrexate. Patients who achieve a clinically relevant response to the first course of treatment may be eligible to receive one re-treatment course of MabThera between weeks 24 and 48. The anticipated time on study treatment is 3-12 months, and the target sample size is 100 individuals.