The pathogenesis of rheumatoid factor (RF), especially IgG RF, in rheumatoid arthritis (RA) and the influence of gold salt on RF were studied clinically. The following results wereobtained. 1) The incidence of RF sera was 78.9% by the RA test, 90.9% by the Heller FⅡ method and 72.7% by the Heller Svartz method. In RA synovial fluid, the incidence of RF was 94% by the RA test, 100% by the Heller FⅡ method and 72.7% by the Heller Svartz method. In osteoarthritis (OA) synovial fluid, the incidence of RF was 14.3% by the RA test and 33.3% by both the Heller FⅡ and Heller Svartz method. 2) The RF titer of same RA serum was higher by the Heller FⅡ method than by the Heller Svartz method. 3) RF response in RA serum and synovial fluid was identical in 76.2% of cases by the RA test. In 19% of the subjects, RA test was positive in synovial fluid but negative in serum. 4) No relationships were found between RF titer and white cell count or RA cell count in RA and OA synovial fluid. 5) The mean value of IgG RF was almost equal in seronegative and seropositive RA. 6) A statistically significant relationship was present between higher erythrocyte sedimentation rate and higher RF titer in RA patients. 7) No relationships were found in positive and negaitve C-reactive protain in the three RF subtypes in RA patients. 8) A correlation was present between a high grade of bone destruction and IgG RF value above the mean in RA serum and synovial fluid. 9) In RA synovial fluid, IgG RF level was parallel to total beta glucuronidase activity. 10) In effective cases of chrysotherapy in RA, serum and synovial fluid gold concentration did not decrease but the IgG RF level decreased slightly. 11) In non-effective cases of chrysotherapy in RA, serum and synovial fluid gold concentration decreased slightly but the IgG RF level was stationary or increased slightly.