This is a randomized (patients are assigned different treatments based on chance), double-blind (neither the patient nor the physician knows whether drug or placebo is being taken, or at what dosage) trial of the safety of anti-tumor necrosis factor (TNF) chimeric monoclonal antibody (Infliximab) in combination with methotrexate (MTX) compared to methotrexate alone in patients with rheumatoid arthritis on standard disease-modifying anti-rheumatic drug background therapy. The purpose of the study is to better understand the safety and occurrence of infections in patients treated with either placebo or 3 mg/kg and 10 mg/kg of infliximab in combination with methotrexate (MTX).