Copper is an essential element that is a cofactor of many enzymes. Copper metabolism is disturbed in Wilson's disease, Menkes disease, primary biliary cirrhosis, and Indian childhood cirrhosis. Copper concentrations increase in acute phase reactions and during the third trimester of pregnancy. Copper concentrations are decreased with nephrosis, malabsorption, and malnutrition. Copper concentrations are also useful to monitor patients, especially preterm newborns, on nutritional supplementation. Results of copper are often interpreted together with ceruloplasmin.