Extensive research has established that scalp hair element levels are related to human systemic levels. The strength of this relationship varies for specific elements, and many researchers consider hair as the tissue of choice for assessing toxic and several nutrient elements. Unlike blood, hair element levels are not regulated by homeostatic mechanisms. Thus, deviations in hair element levels often appear prior to overt symptoms and can thereby be a valuable preliminary tool for predicting the development of physiological abnormalities.