The purpose of this study was to investigate the diagnostic utilities of anti-agalactosyl IgG antibody (CARF), anti-cyclic citrullinated peptide (CCP) antibody and rheumatoid factor (RF) in rheumatoid arthritis (RA), non-RA rheumatic diseases, and chronic viral hepatitis. The authors determined serum levels of CARF and anti-CCP2 by ELISA and IgM-RF by a immunonephelometric method in 834 controls and in 397 patients with the following conditions: RA (100), non-RA rheumatic diseases [systemic lupus erythematosus (SLE) 30, primary Sjogren's syndrome 18, systemic sclerosis 30, inflammatory myositis 19], chronic viral hepatitis B and C (HBV 100, HCV 100). The sensitivities of CARF (83%) and anti-CCP (85%) were significantly higher than that of RF (75%, p = 0.01, respectively) in RA, and the specificity of anti-CCP (98%) was significantly higher than those of CARF (92%) and RF (90%, p < 0.001, respectively). A comparison of receiver operating characteristic (ROC) curves revealed that the diagnostic accuracies of CARF and anti-CCP were superior to that of RF (CARF vs. RF, p = 0.008, anti-CCP vs. RF, p = 0.017) in RA. CARF positivity was significantly higher than those of anti-CCP (p = 0.007) and RF (p = 0.008) in systemic sclerosis, and the positivity of CARF was significantly higher than that of anti-CCP in Sjogren's syndrome (p = 0.016). Furthermore, CARF had significantly higher positivity than anti-CCP or RF in chronic viral hepatitis B and C. Finally, the titers of these three markers in RA were significantly higher than in non-RA rheumatic diseases and in chronic viral hepatitis B and C. Our results suggest that anti-CCP is the most useful serologic marker for the differentiation of RA and non-RA rheumatic diseases, and chronic viral hepatitis B and C.