This study is designed to compare a range of doses of GW856553 versus placebo on the biomarkers associated with rheumatoid arthritis

Inclusion criteria:

• Must have a diagnosis of RA according to the revised 1987 criteria of the American College of Rheumatology.
• Must have 3 or more swollen or 3 or more tender/painful joints at screening.
• Must be on stable weekly methotrexate (2.5mg-25mg) for at least eight weeks prior to screening.

Exclusion criteria:

• Must not be morbidly obese.