The abilities of brans from the cereals barley, oats, maize, rice, and wheat to adsorb in vitro the hydrophobic, environmental mutagen 1,8-dinitropyrene (DNP) were investigated using a mutagenicity assay. These brans were obtained from known cultivars using defined milling conditions and were chemically characterised. The abilities of total and insoluble dietary fibre preparations obtained from these brans to adsorb DNP were also investigated. The predicted weight of each bran required to adsorb 50% of the added DNP was used to compare the adsorptive abilities of the different brans. The brans were ranked in the order (most effective to least effective): rice, wheat, maize, barley, and oats. The adsorptive abilities of the dietary fibre preparations were not significantly different from the bran from which they were prepared. However, if the dietary fibres (cell walls) were the only components adsorbing the DNP, we would have expected the dietary fibre preparations to have adsorbed more DNP than the equivalent unextracted bran. This suggests that other components, probably starch, also adsorb DNP in the unextracted brans. It is not known why brans from different cereal species differ in adsorptive ability but the lignified cell walls in wheat bran may be important in conferring good adsorptive properties to this bran. The possible relationship between adsorptive ability and ability of the bran from a particular species to protect against colorectal cancer is discussed.