This study will evaluate the efficacy and safety of ocrelizumab, compared to placebo, in patients with active rheumatoid arthritis who have an inadequate response to methotrexate therapy. Patients will be randomized 2:2:1 to receive 1) infusions of ocrelizumab 200mg iv on Days 1 and 15, 2) infusions of ocrelizumab 400mg iv on Day 1 and placebo iv on Day 15, or 3) infusions of placebo iv on Days 1 and 15. At the end of the placebo-controlled treatment period at 24 weeks, patients in groups 1 and 3 will be re-randomized to receive either a single infusion of 400mg iv ocrelizumab or 2 infusions of 200mg iv ocrelizumab, and group 2 will receive a second single infusion of 400mg iv ocrelizumab. All patients will receive a stable dose of concomitant methotrexate (7.5-25mg/week) throughout the study. The anticipated time on study treatment is 1-2 years. Target number of patients to be enrolled in this trial is 300.