Rheumatoid arthritis (RA) is a common autoimmune disease characterized by immune cell infiltration of the synovium, leading to the loss of cartilage, bone, and joint function. Although regulatory T (T-reg) cells are thought to modulate the initiation and progression of RA, a consensus has yet to be reached regarding the function and composition of T-reg cells in RA patients. To address these discrepancies, we analyzed not only the total T-reg frequency but also that of T-reg subpopulations in the peripheral blood of RA patients and healthy controls by flow cytometry. We found that the total T-reg population was not significantly different between RA and control subjects. However, the effector T-reg cell subgroup, defined as CD45RA(-)CD25(hi), showed markedly decreased frequency in RA patients. In addition, the total T-reg population from RA patients showed a significant decline in the expression of CD25. Both the naive and effector T-reg subgroups also showed marked reduction of CD25 expression in RA patients compared to controls. These data suggest that the decreased frequency of effector T-reg cells and overall reduction of CD25 expression in T-reg cells in the peripheral blood may be evidence of altered T-reg homeostasis associated with RA pathogenesis.