The local release of inflammatory mediators are intricately linked with initiation and propagation of the inflammatory reaction in ulcerative colitis (UC) and Crohn's disease. We have used immunohistochemical staining of colonic biopsies to determine the cell of origin and the location of the cells which synthesize of TNF-alpha and IL-1 beta in patients with UC and Crohn's colitis. Patients were chosen from children aged 7-16 years, who had UC or Crohn's diagnosed following review of colonic biopsies taken during colonoscopy. The patients reviewed had not received treatment for inflammatory bowel disease. Paraffin embedded colonic biopsies were sectioned, deparaffinized, and stained with mouse monoclonal IgG antibodies directed against human recombinant TNF-alpha and IL-1 beta. The colonic lamina propria of all biopsies from patients with UC or Crohn's colitis was expanded with a mixed mononuclear, polymorphonuclear, lymphocytic, and plasmacytic infiltrate. Mononuclear cells distributed throughout the interstitium, stained prominently for both TNF-alpha and IL-1 beta. Plasmacytes, polymorphonuclear leukocytes, small lymphocytes, and foamy macrophages did not stain for either TNF-alpha or IL-1 beta. Transmigrating mononuclear cells in crypt epithelium also stained brightly for both TNF-alpha and IL-1 beta. Colonic epithelial cells did not stain for either TNF-alpha or IL-1 beta.(ABSTRACT TRUNCATED AT 250 WORDS)