TNF and rheumatoid arthritis: That therapy with a biological against TNF could be used as a marker of disease severity in this study is also due to the fact that its use is strictly regulated in the Netherlands; therapy with biologicals against TNF is available for all RA-patients that failed on two DMARDs and still have active disease (DAS28 > 3.2) despite therapy with methotrexate 25 mg weekly or at the maximal tolerated dose.