The levels of rheumatoid factor (RF), antinuclear antibody (ANA), and composition of peripheral lymphocyte subsets in 515 dogs were examined. Of these sample cases, 33 cases were diagnosed as immune-mediated fever that presented with high C-reactive protein (CRP), 31 cases were diagnosed with Hansen's Type 1 disc herniation and the remaining 415 cases were clinically healthy dogs, and served as controls. In the cases diagnosed with immune-mediated fever, 84% of the dogs tested positive to either RF or ANA (RF positive 60.6%
ANA positive 24.2%). By contrast, 16.2% of the healthy dogs were positive for either RF or ANA (RF positive 14.9%
ANA 1.3%). The CD4/CD8 ratio for peripheral lymphocyte was high for all analysed cases diagnosed with immune-mediated fever, and was significantly higher than those of healthy controls. These results indicate that the abnormal levels of lymphocytes may be an effective indicator for immune-mediated disease coupled to immune-mediated fever.