The ability of three kinds of fiber to bind to 2-amino-3-methylimidazo[4,5-f]quinoline (IQ), a potent bacterial mutagen formed during the cooking of meat, was investigated to determine interactions among important food components. At pH 6.5 corn bran, wheat bran, and alfalfa meal each bound approximately 50% of the available IQ after incubation for 1 hour. Binding was pH-dependent, occurred optimally between pH 4 and 6, and was probably due to a cation-exchange mechanism. The pH at which IQ is efficiently bound to fiber overlaps the range of pH in the human gastrointestinal tract.