The ability of oral doses of copper oxide powder to raise liver and blood copper concentration was examined in penned sheep given a pelleted diet containing 4 mg of copper per kg dry matter. Merino sheep of similar live weight and liver copper concentration were allocated at random to one of six treatment groups of four sheep each. Treatment groups received nil, 2.5 g, 5 g, 10 g, 20 g and 40 g of cupric oxide powder. The cupric oxide powder of sieve size 250-350 microns was effective in raising the liver copper concentration for at least 12 weeks. The large particles of oxide powder were retained in the gut for at least 13 days after dosing. Sheep given 10-40 g doses of cupric oxide powder were at risk of copper toxicity, as indicated by elevated plasma enzyme activities, liver copper concentrations and reduced liveweight gains. It was concluded that a 2.5 g dose of cupric oxide powder could be used to prevent short periods of copper deficiency in sheep at pasture without risk of copper toxicity.