Suppression of chronic intestinal inflammation by different subtypes of T cells has been described in recent years. In particular, naturally arising CD4(+)CD25(+) regulatory T cells and IL-10-producing regulatory T cell type 1 CD4(+) T lymphocytes have been implicated in the regulation of intestinal inflammation. Here we focus on the ability of CD4(+)CD25(+) regulatory T cells to suppress innate and T-cell responses and discuss implications for immunoregulation in human inflammatory bowel disease. Besides the modulation of lymphoproliferation, a role for CD4(+)CD25(+) T cells in down-modulation of innate immune responses is emerging and the immunoregulatory activities of regulatory T cells in vivo may be mediated via effects on dendritic cells. Considering the extraordinary regenerative potential of the intestinal mucosa, the ability to impede pathogenic T-cell responses by active regulation might be of particular therapeutic benefit for the treatment of chronic intestinal inflammatory diseases such as Crohn's disease and ulcerative colitis.