OBJECTIVE To investigate the effect of filtration plasmapheresis (DFPP) on blood contents of rheumatoid factor (RF), C reactive protein (CRP), and erythrocyte sedimentation rate (ESR) in patients with rheumatoid arthritis (RA) in active stage, and to appraise the therapeutic effect of DFPP on RA. METHODS The changes in contents of blood RF, CRP, ESR before and after DFPP were compared. The treatment was given for 2-3 times, and the activity of RA and the appearance of filtrate plasma were compared before and after the treatment. RESULTS There were dramatic reductions of the levels of RF, CRP, ESR after single DFPP by 22.55%, 57.08% and 50.48%, respectively, compared with those before the treatment (all P<0.001). The color of the filtrate was green in RA in active stage. The cases with dark green filtrate had higher active indexes (pain, tenderness, swelling) and blood contents of CRP and ESR than those with green or yellow-green ones (all P<0.001). CONCLUSION DFPP can remarkably reduce the level of RF, CRP, ESR of blood. The filtrate of RA in active stage appeared green. There is a relationship between the activity of RA and the color of filtrates.