Cytokine production from peripheral blood mononuclear cells, T-cell subsets and Ia positive monocytes in patients with inflammatory bowel disease were investigated. 26 patients with Crohn's disease (CD), 7 patients with ulcerative colitis (UC) and age and sex matched healthy donors (HD) as controls were studied. No differences were seen between UC and HD in any of the parameters examined. However, impairment of interleukin 2 and interferon production was noted in CD. They cannot be attributable to decreased number of T cells, because no significant differences were seen in the number of T cells including subsets. On the other hand, regarding interleukin 1 production, no differences were seen between HD and CD. These results suggest that some form of dysfunction exists at the T-cell level in the peripheral blood in CD.