BACKGROUND: B lymphocytes are implicated in the pathogenesis of multiple sclerosis. We aimed to assess efficacy and safety of two dose regimens of the humanised anti-CD20 monoclonal antibody ocrelizumab in patients with relapsing-remitting multiple sclerosis.METHODS: We did a multicentre, randomised, parallel, double-blind, placebo-controlled study involving 79 centres in 20 countries. Patients aged 18-55 years with relapsing-remitting multiple sclerosis were randomly assigned (1:1:1:1) via an interactive voice response system to receive either placebo, low-dose (600 mg) or high-dose (2000 mg) ocrelizumab in two doses on days 1 and 15, or intramuscular interferon beta-1a (30 ìg) once a week.