The dietary intakes of copper by children and adults who consume free diets are often significantly lower than the recommended daily allowances of the National Academy of Sciences (USA) or the World Health Organization. These lower-than-recommended intakes of copper appear to be adequate for healthy individuals since states of copper deficiency have not been observed in the absence of an accompanying metabolic disorder. Copper deficiencies have arisen in pre-term infants of low birth weight as a result of breast-milk diets, and in children and adults as a result of fluids that are used for total parenteral nutrition. This paper describes the use of trace-metal balance studies to evaluate the adequacy of copper intake from these sources and from synthetic diets that are used in the treatment of inherited and acquired metabolic disorders.