We review evidence that red and processed meat are causes of colon cancer and that processed meat is a risk factor for childhood cancer and type 2 diabetes. Associations could be due to N-nitroso compounds (NOCs) derived from nitrosation of NOC precursors (NOCPs). We review our survey of total NOC and NOCP content of foods. Only rapidly nitrosated amines, including a glycosyl amino acid, were efficiently determined as NOCPs. NOCPs in hot dogs and rat feces were partly purified by adsorption-desorption and HPLC. After nitrosation, purified hot dog fractions were directly mutagenic in Ames test. The main NOCPs in these materials may be N-glycosyl amino acids and peptides. NOC levels in rat gastrointestinal tract rose steadily from stomach to feces. NOCP levels showed similar trend but with sharp increases from stomach to duodenum. One day after Min and C57BL/6J mice were fed 4% dextran sulfate sodium to induce acute colitis, fecal NOC levels increased 1.9-fold compared with untreated mice (P < 0.05). For 7 d Swiss mice received semipurified diet, 180 g beef-pork hot dogs mixed with 820 g diet or 180 g sautéed beef mixed with 820 g diet. Fecal NOC outputs on day 7 were 3.7-5.0 (hot dog) and 2.0-2.9 (beef) times those for control groups (P < 0.002 for combined groups), perhaps reflecting higher dietary NOC intakes. Feeding a similar hot dog mixture to mice did not affect normal 7-methyldeoxyguanosine level in colonic mucosal DNA. Overall, results support the hypothesis that colonic NOCs are a cause of colon cancer.