Part A: 30 patients suffering from active rheumatoid arthritis despite continued treatment with methotrexate will receive once daily two capsules containing either GLPG0259 (25 mg/capsule) or matching placebo, for 12 weeks. In the course of the study the patients will be examined for severity of disease, as well as for any adverse effects that may occur. If needed, dosing may be split to one capsule twice daily, or reduced to one capsule of 25 mg.