IL-10 has anti-inflammatory and immunoregulatory properties that suggest a potential therapeutic role in RA. IL-10 inhibits proinflammatory cytokine and chemokine production in addition to blocking T-cell responses to specific antigens. It acts primarily through inhibition of costimulatory properties of macrophages. IL-10 stimulates proliferation and differentiation of antibody-forming B-cells. Preclinical studies in a variety of animal models, including collagen-induced arthritis, have shown that IL-10 is effective in preventing or inhibiting inflammation and autoreactivity. Although in RA, circulating and synovial levels of IL-10 are increased, accumulated evidence suggests that there may be a relative deficit of available IL-10. Moreover, exogenous addition of IL-10 in vitro has been shown to affect the immunopathological processes involved in RA. Preliminary studies of human recombinant IL-10 in patients with RA have demonstrated a trend towards efficacy with a good safety profile. Taken together, the data support a therapeutic role for IL-10 in the treatment of RA.