- Must have a diagnosis of active rheumatoid arthritis (RA) (according to the revised 1987 criteria of the ARA (American Rheumatism Association) with at least 4 swollen and 4 tender joints for at least 3 months prior to screening - Have been treated with and tolerated methotrexate (MTX) at a dose of at least 15 mg per week for at least 3 months prior to screening - Have been on a stable MTX dose of greater than or equal to 15 mg per week and less than or eual to 25 mg per week for at least 4 weeks prior to screening - If using non steroidal anti-inflammatory agents (such as naproxen) or other pain relievers for RA, must be on a stable dose for at least 2 weeks prior to the first administration of study agent