The consequences of iron deprivation on iron-containing enzymes of different tissues in rat and/or human is reviewed. Iron participates in a wide variety of biochemical processes, including mitochondrial electron transport, catecholamine metabolism and DNA synthesis. Recently, a broad spectrum of biochemical abnormalities resulting from iron deficiency have been described. Effects on skeletal muscle, cardiac muscle, brain tissue, liver tissue gastrointestinal tractus, body temperature regulation, DNA synthesis are successively discussed. The key liabilities of tissue iron deficiency, even at a mild degree relate to decrease in intellectual performance, and in physical capacity during exercise, alteration of temperature regulation, immune function.