The ability of 22 strains of intestinal bacteria to bind the mutagenic pyrolyzates—3-amino-1 ,4-dimethyl-5H-pyrido[4,3-b]indole [(Trp-P-1) CAS: 62450-06-0), 3-amino-1-methyl-5H-pyrido[4,3-b]indole [(Trp-P-2) CAS: 62450-07-1), 2-amino-6-methyldipyrido[1.2-a:3′,2′-d]imidazole [(Glu-P-1) CAS: 67730-11-4], 2-aminodipyrido[1.2-a:3′,2′-d]imidazole [(Glu-P-2) CAS: 67730-10-3], 2-amino-3-methylimidazo[4,5-f]quinoline [(IQ) CAS: 76180-96-6], 2-amino-3,4-dimethylimidazo[4,5-f]quinoline [(MeIQx) CAS: 77094-11-2], and 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline [(MeIQx) CAS: 77500-04-0)—was investigated and compared to their ability to bind to some dietary fibers (corn bran, apple pulp, soy bean fiber, cellulose, chitin, and chitosan). The pyrolyzates are potent mutagenic and carcinogenic heterocyclic amines formed during cooking. Solution of these amines was mixed with aqueous suspension of bacterial cells or dietary fibers, and removal of these amines from the reaction mixture by centrifugation was defined as the binding. Trp-P-1 and Trp-P-2 were effectively bound to all gram-positive and some gram-negative bacterial cells, corn bran, apple pulp, and soy bean fiber. Binding of Trp-P-1 and Trp-P-2 to Escherichia coli, Klebsiella pneumoniae, and cellulose was moderate, and to chitin and chitosan it was little. None but corn bran bound Glu-P-1 and Glu-P-2 effectively. Corn bran effectively bound all mutagens tested. The quantity of the binding of IQ, MeIQ, and MeIQx was dependent on the strain of bacteria and the kind of fiber. The mechanism of binding of Trp-P-2 to freeze-dried feces, Lactobacillus casei YIT 9018 (LC9018), and corn bran was investigated. The binding was pH dependent, occurred instantaneously, and was inhibited by the addition of metal salts. These results indicate that the binding was mostly due to a cation-exchange mechanism, but some irreversible binding of Trp-P-2 was observed, most notably to freeze-dried feces. The mutagenicity of Trp-P-2 for Salmonella typhimurium TA98 in the presence of S9 mix was inhibited by the addition of LC9018 or corn bran to the reaction mixture. The results indicate that bound Trp-P-2 did not cause mutation under the assay conditions.