Methods for the control of induced or simple hypocupraemia in cattle were tested using a free-choice copper supplement or by adding a soluble copper salt to the water supply, using a specially designed proportioner. In molybdenum induced hypocupraemia the provision of a free-choice supplement containing 2500 mg Cu per kg resulted in only 10 out of 18 of the cows tested having adequate serum copper levels after a five month grazing period. Supplementation of water supplies to a level of 5 mg Cu per litre was effective in raising and maintaining serum copper at normal levels in a herd of low copper status when offered for a similar period. In experimentally produced molybdenosis, 2 to 3 mg per litre in drinking water corrected the associated diarrhoea and abolished the anomalous blood fractions found at high levels of molybdenum intake in three and five days respectively. It is suggested that water supplementation using a proportioner such as the one described is an effective way of combating both simple and induced hypocupraemia in grazing cattle.