B cells play an important role in the development of autoimmune diseases due to their production of autoantibodies, antigen-presenting capacity and production of pro-inflammatory cytokines. The purpose of the present study was to analyse B cells from rheumatoid arthritis (RA) and systemic lupus erythematosus (SLE) patients, with respect to their expression of the IL-2 receptor (IL-2R) subunit CD25. Using flow cytometry, we found that CD25+ B cells from RA patients expressed significantly higher frequencies of CD122 and CD132 than CD25+ B cells from control subjects, indicating a fully functional IL-2R. These CD25+ B cells also expressed higher frequencies of the co-stimulatory molecule CD80, whereas IgM and IgA expression was decreased compared with CD25+ B cells from healthy controls. In addition B cells from SLE patients co-expressed CD25 together with CD80, CD122, and CD132, but to a lower degree IgD and IgM, when compared with healthy controls. Taken together, our results indicate that CD25+ B cells from RA and SLE patients are in a highly activated state, display a more mature phenotype and suggest that this B cell subset may be involved in the pathogenesis of RA and SLE.