Experiments were conducted with young chicks to investigate the mechanism by which various feed ingredients reduce the bioavailability of inorganic Mn. Although corn, soybean meal (SBM), fish meal (FM), wheat bran (WB), and rice bran (RB) contain significant quantities of Mn, these feed ingredients when added to a casein-dextrose diet have been shown to reduce Mn deposition in key tissues (i.e., bone, pancreas, and gallbladder). Studies reported herein indicate that reduction in tissue Mn concentration due to feed ingredient supplementation resulted from reduced Mn absorption, rather than from enhanced Mn excretion. Feedstuffs exerted their effect primarily at the gut level, although some Mn binding may also have occurred in body fluids. Fractionation of each feed ingredient indicated that the neutral detergent fiber (NDF) fraction of WB and a corn-SBM mixture accounted for virtually all of the Mn-binding capabilities of these ingredients. In contrast, ash fraction was responsible for tissue Mn-lowering capabilities of FM. Both NDF and ash fractions of RB significantly lowered tissue Mn concentrations, but not to the same extent as that caused by RB itself. A significant portion (11 to 27%) of the total quantity of copper was found in the NDF fraction of all feed ingredients. Over 12% of the magnesium and iron in FM was contained in the NDF fraction, while 20% of the magnesium in WB and 15% of the iron in RB was likewise present in the NDF fraction. Very little K, Zn, or Mn was associated with the NDF fraction of any feed ingredients. All Ca in WB but less than 1% of Ca in RB were present in the NDF.