Infliximab, a chimeric anti-TNF alpha antibody, showed in two double-blind placebo-controlled trials efficacy in combination with methotrexate (MTX) in patients with severe rheumatoid arthritis (RA). Whereas in the first trial low-dose MTX or placebo was compared to infliximab alone and in combination, the second trial compared infliximab to placebo in patients with active RA despite maximal tolerated MTX treatment. Infliximab showed synergistic effects in combination with MTX. The immunogenicity of infliximab was reduced by the combination. Infliximab in combination with high-dose MTX is effective and safe in long-term treatment up to 54 weeks.