THE importance of copper in the metabolism of iron has been recognized since Hart et al.1 showed that rats become anaemic when fed a diet composed solely of milk, and respond to the administration of iron only if copper is provided in addition. The observation made by a number of workers that, following the administration of copper to rats deficient in copper, the concentration of iron in their livers is reduced and that of haemoglobin increased has led to the assumption that copper is required for the utilization of iron2. The possibility that copper may be involved specifically in the release of iron from storage sites has not been investigated.