It follows from the data studied that information on the content of chemical elements in animal hair, depending on the presence of melanin, should be related to the concentration of this pigment, before judging the effect of environmental factors on their content. For a long time it was assumed that, the entry of mineral substances into the hair occurs from the blood capillaries, which are supplied to the hair follicle bulbs and the epithelial layers of the skin. There have been attempts to establish a positive correlation between the content of mineral and organic substances in the blood. When comparing the reaction of blood plasma and rat hair to a change in the composition of food, it was found that plasma quickly responds to changes in the content of magnesium and calcium in the diet, slowly - to the content of phosphorus and does not react at all to changes in the level of sodium and calcium (this is explained by a clear homeostatic regulation of the content of these elements in the blood). At the same time, the hair reacts quickly to changes in sodium content, slowly to calcium, magnesium, phosphorus, and very slowly to changes in potassium concentration.