Recently, the alteration of peripheral T cells has become a focus of attention in research on Crohn's disease (CD). To examine the characteristics of peripheral T cells in CD patients, we analyzed the expression of a memory T cell marker (CD45RO(Bright)CD3+) and the cytokine production by peripheral helper and cytotoxic T cells in patients with CD. With the use of monensin to prevent the secretion of cytokines under stimulation, we measured the count of intracellular cytokine-positive cells for production of interferon (IFN)-gamma, tumor necrosis factor (TNF)-alpha, interleukin (IL)-2, IL-4, IL-6, IL-10, and granulocyte-macrophage colony stimulating factor (GM-CSF) in the peripheral T cell population using flow-cytometry. The counts of lymphocytes, T cells, and helper T cells in patients with CD were significantly lower than in normal volunteers. Although no difference in the counts of lymphocytes, total T cells, helper and cytotoxic T cells was observed, the counts of intracellular cytokine producing helper T cells in IFN-gamma, TNF-alpha or GM-CSF were significantly higher in active cases than in quiescent cases. These results suggest that stable CD patients are immunosuppressive, and activation of some kinds of T-cells, especially Th1-associated cytokine producing T-cells, correlate with disease progression. Th1-associated cytokine analysis of peripheral T cells may be one of the useful markers to evaluate the activeness of Crohn's disease.