Rituximab, an anti-CD20 monoclonal antibody, is a new alternative treatment for patients with severe immune diseases and resistance to conventional treatment. One of the mechanisms of action of this drug is the complement-mediated lysis. Most RA patients respond well to rituximab treatment, however, some are refractory and mechanism of this non-response is still unclear. The role of CD55 and CD59 protein and its overexpression as a mechanism of resistance to rituximab treatment in lymphoma patients have been investigated. However, there has not been studied a correlation between the intensity of expression of these regulatory molecules on B cells of RA patients and resistance to treatment with Rituximab.