The topic of absorption of Fe has been reviewed by L. Hallberg, E. R. Morris, and C. A. Finch and J. D. Cook. Food Fe can be classified into heme Fe from hemoglobin and myoglobin and nonheme Fe largely supplied by cereals, fruit, and vegetables. In general, ferric compounds were less effectively utilized, although the Fe salts of ethylenediaminetetraacetic acid (EDTA), ammonium citrate, and choline citrate were utilized as well as the ferrous sulfate. The availability of Fe from its various salts for human subjects may be inferred from studies by H. Brise and Hallberg. In studies on the effect of chelating agents on the availability of trace elements for chicks from diets containing isolated soybean protein, it was found that EDTA reduced the availability of Fe while it improved the availability of Zn and some other trace elements. Thermodynamic constants do not permit prediction of the bioavailability, toxicity, and metabolism of Fe-chelating drugs.