While the major impetus of most of our present knowledge of these metals emphasizes their deficiencies or toxicities, little has been done on their metabolic interactions. Such interactions acknowledge the importance of nutritional deficiencies or toxicities in the biospheres. The effect of dietary zinc supplementation on the bioavailability of copper and iron is a matter of conjecture. Likewise, further research is needed before a unifying hypothesis can be established on the effect of imbalances or interactions among copper and iron. Such mineral imbalance studies will be of value in determining their dietary requirements and in appraising circumstances in which risk to human and animal health may arise.