Effective control of copper poisoning in sheep was obtained by the subcutaneous injection of ammonium tetrathiomolybdate. Three doses, each of 3.4 mg/kg bodyweight, were given on alternate days. This treatment caused a substantial reduction in liver copper content and in liver damage. It also decreased the mortality rate in animals that had developed the haemolytic crisis. The subcutaneous route is as effective as the intravenous route and is more convenient. No adverse side-effects of the treatment were observed.