Elements essential for humans, their toxicologic effects, relationship between tissue concentration of elements and health indices, interaction of elements among themselves and with dietary components, bioavailability, and the assessment of human health status based on tissue element concentrations are reviewed. Twenty six elements are considered important to humans. Arsenic (7440382), cobalt (7440484), fluorine (7782414), iron (7439896), molybdenum (7439987), selenium (7782492), vanadium (7440622), chromium (7440473), copper, (7440508), iodine (7553562), manganese (7439965), nickel (7440020), silicon (7440213), and zinc (7440666) are essential in trace amounts. Calcium (7440702), chlorine (7782505), magnesium (7439954), phosphorus (7723140), potassium (7440097), and sodium (7440235) are essential in macro quantities. Lithium (7439932) and antimony (7440360) are possibly essential. Aluminum (7429905), cadmium (7440439), lead (7439921), and mercury (7439976) are toxic non essential elements. Tissue element concentrations may be correlated with health indices in the deficiency range for an essential element and in the toxicosis range for an essential or non essential toxic element. Tissues that respond to variation in intake include the liver, kidney, bone, and whole blood or blood components. Rapid changes in tissue mineral concentration are helpful in defining changes in health status. Evidence has accumulated to show that almost every element interacts with other elements either directly or indirectly. The consumption of excessive dietary supplements is a potential source of adverse health effects. For example supplemental zinc can decrease liver concentrations of iron, copper, and manganese in young Japanese-quail. Food is the primary route through which individuals are exposed to the toxic elements lead, cadmium, and mercury. The concentration of the element in food, the dietary composition, and nutritional status of the host are all important in assessing adverse health effects. Tissue mineral concentrations have been used to assess health status of humans.