The object of the investigation reported here was to obtain some insight into the mode of specific binding of iron by conalbumin. To this end the protein was modified in a variety of ways by denaturing treatments or chemical reactions, and the iron- binding activities of the intact and modified proteins were studied by chemical and microbiological assays. The activity was found dependent upon the integrity of the protein molecule and involves most of the reactive groups. As has been found with siderophilin, conalbumin was found to bind copper in a similar but more labile manner than iron.