Rituximab (RTX) is a murine/human monoclonal antibody to CD20, a protein expressed almost exclusively on human B-lymphocytes. RTX induces rapid and marked B-cell depletion with beneficial clinical effects in 1/3 to 1/2 of rheumatoid arthritis patients. Treatment is given as two iv. infusions with a two-week interval and in combination with methotrexate. Mild to moderate side-effects are frequent, particularly during the first infusion, but long-term side-effects are generally rare, although pulmonary events and reactivation of viral infections of the liver is of concern.