The recent clinical practices for rheumatoid arthritis have changed greatly. First, biologic agents such as tumor necrosis factor blocker have been developed as well as disease-modifying antirheumatic drugs, with great efficacy in intractable RA. On the other hand, the importance of early effective therapeutic intervention has been recognized since early treatment prevents the progression of joint damage. However, early diagnosis of RA is not so easy because of the lack of appropriate diagnostic criteria. New laboratory tests have appeared for the diagnosis and prognostic prediction of RA. Among them, anticyclic citrullinated peptide antibodies (anti-CCP), which bind epitopes containing citrulline, seem to be attracting the most attention. Although rheumatoid factor (RF) is the only serologic marker among the seven classification criteria of the American College of Rheumatology (ACR) for RA, variability of the RF assay within laboratories and/or between laboratories, and quality assurance has not been established. We must address the standardization of RF assay as soon as possible.