The distribution of tissue kallikrein (TK) and its plasma inhibitor, kallistatin in plasma and intestinal tissue, was studied in patients with active ulcerative colitis (UC) and Crohn's disease (CD). TK was localized to goblet cells and kallistatin to epithelial cells of normal human intestine. Both proteins are visualized in macrophages inside granulomas in CD as well as in plasmocytes in both CD and UC. Intestinal tissue kallikrein (ITK) and kallistatin are significantly decreased in inflamed intestine compared to noninflammatory controls. TK mRNA is significantly decreased in intestinal biopsy samples from active UC patients compared with inactive patients or controls. Immunoreactive TK is present in plasma in very low concentrations in patients and did not differ in normal subjects. Plasma kallistatin was significantly decreased in patients with active disease compared to normal controls. Our data suggest that release of TK during inflammation plays a role in inflammatory bowel disease.