OBJECTIVE: This study was designed to investigate CD20dim expression on T cells between healthy control subjects and rheumatoid arthritis patients and to investigate the association between CD20dim T cells and clinical manifestations in rheumatoid arthritis. METHODS: Peripheral bloods from twenty seven healthy controls and twenty six rheumatoid patients were evaluated by dual color immunophenotyping. We used IgGla and IgG2a for negative control, then, divided T cells and B cells on CD3/CD19 combination. And we evaluated two subpopulation CD5+CD20dim T cell (CD20dim T cell) and CD5+CD20bright cell(CD5 B cell) on CD5/20 combination for comparison. In order to correlate the CD20dim T cell datas with patient's clinical status, patients charateristcs such as age, disease duration, morning stiffness, rheumatoid factor(RF), and antinuclear antibody(ANA) were reviewed. RESULTS: The mean percent positivity of T cells(CD3) and B cells(CD19) in 27 healthy control donors was 63.2+/-7.7%, and 11.4+/-2.6 %. The mean percentages of CD20dim T cell and CD5 B cell(Leul) were 2.3+/-1.0% and 1.4+/-0.9% and upper limit of reference values of CD20dim T cells and CD5 B cells(Leul) that calculated from normal healthy controls were 4.3%0 and 3. 2 %. Compared with healthy controls, CD20dim T cells were significantly elevated in total patient groups(4.4+/-2.7%, p(0.01). and significantly increased more than upper limit of reference values in eleven of 26 patients. Compared with CD20dim T cells according to disease duration, disease duration of most patients(10/11) with elevated CD20dim T cell were less than 2 years. CONCLUSION: The results indicated that CD20dim T cells were expressed at low levels in healthy controls but elevated levels of CD20dim T cells in rheumatoid arthritis patients were observed and close relationship to CD20dim T cells expression and disease duration was noted.