Parenteral treatments can provide a rapid successful method of supplementing ruminants with copper and selenium, and avoid the possible interactions between an oral supplement and other dietary constituents. The copper preparations studied contained copper complexed with calcium edetate (EDTA) or copper methionate , copper oxide or copper oxyquinoline sulphonate. The recommended doses of these commercial preparations contain different amounts of copper only part of which is transferred to the liver stores from which it can be released during the following months. The recommended dose of copper oxyquinoline sulphonate contains only 12 mg copper and the duration of its protective effect is short. Only a small proportion of the copper in copper methionate and copper oxide is transferred to the liver whereas nearly all the copper in a single dose of the EDTA complex (50 mg copper for sheep) is transferred to the liver stores. Although no longer recommended for use in sheep the copper EDTA complex can be administered to cattle to provide up to 1 mg copper/kg bodyweight. Selenium deficiency in both cattle and sheep can be corrected by the subcutaneous administration of up to 0.15 mg selenium/kg bodyweight as sodium selenate. However, if a dietary deficiency persists copper and selenium treatments are effective for only a few months. To avoid the need for repeated treatments, slowly dissolving or controlled release systems have been developed. Subcutaneous depots of barium selenate have been used (1 mg selenium/kg bodyweight) but large residues remained at the site of injection for up to three months. Initial trials with controlled release glasses containing copper have shown that they maybe useful for routine parenteral therapy.