In the preparation of experimental diets for mineral research, it is frequently difficult to obtain a combination of feedstuffs which will be sufficiently low in the mineral to be studied and still be adequate nutritionally. It is usually the protein-rich ingredients which pose the greatest problem, since it is necessary to have the diet adequate in amino acids, and protein sources such as animal or oilseed are usually sources of minerals in various amounts. The use of ethylenediaminetetraacetic acid (EDTA) to lower the mineral content of dietary ingredients has been very useful for Fe, Zn, and Ca studies. From the reduced mineral content of the treated isolated soybean protein, it is probable that the method could be useful in developing deficient diets for the study of several other minerals as well. The EDTA treatment method used for the soybean protein was modified to treat the blood fibrin.