Because colonic N-nitroso compounds (NOC) may be a cause of colon cancer, we determined total NOC levels by Walters' method in the gastrointestinal tract and feces of rodents: (i) feces of C57BL mice fed chow and semi-purified diets contained 3.2 +/- 0.4 and 0.46 +/- 0.06 NOC/g, respectively (P < 0.01, mean +/- SD). (ii) NOC levels for gastrointestinal contents of three groups of Sprague-Dawley rats fed chow diet were 0.9 +/- 0.05 (diet), 0.2 +/- 0 (stomach), 0.3-0.4 (small intestine), 0.7-1.6 (cecum and colon) and 2.6 +/- 0.6 (feces) nmol/g. NOC precursor (NOCP) levels (measured as NOC after mild nitrosation) for two rat groups fed chow diet showed a 16-fold increase from stomach to proximal small intestine (mean, 6.2 micromol/g), and a 1.7-fold increase from distal colon to feces (mean, 11.6 micromol/g). (iii) Eight Min and five C57BL/6J mice received 4% dextran sulfate sodium in drinking water on days 1-4 to induce acute colitis. This increased fecal NOC levels 1.9-fold on day 5 in both strains (P < or = 0.04), probably due to NO synthase-derived nitrosating agents in the colon. (iv) Following studies on humans fed beef [Hughes et al. (2001) Carcinogenesis, 22, 199], Swiss mice received semi-purified diets mixed with 18% of beef plus pork hot dogs or sautéed beef for 7 days. On day 7, individual 24-h fecal NOC outputs were determined. In three hot dog and two beef groups with 5 mice/group, mean fecal NOC output/day was 3.7-5.0 (hot dog) and 2.0-2.9 (beef) times that for control groups fed semi-purified diet alone (P < 0.002 for each of combined groups). These groups showed little change in fecal NOCP output. (v) Initial purification of rat fecal NOCP by adsorption-desorption and HPLC is described. Results should help evaluate the view that colonic NOC causes colon cancer associated with colitis and ingestion of red and nitrite-preserved meat.