Forty-five adult SA Mutton Merino ewes and 36 eight-month-old ram lambs were divided into three groups so that each group contained an equal number of animals of each haemoglobin type AA, AB and BB. Three diets were compiled. The control diet (C) contained 8,02 mg Cu/kg, 1,3 mg Mo/kg and 0,22% S; the molybdenum supplemented diet (M) contained 3,45 mg Cu/kg, 40,0 mg Mo/kg and 0,22% S; and the molybdenum and sulphate (MS) supplemented diet 3,55 mg Cu/kg, 38 mg Mo/kg and 0,34% S. After receiving these diets for a period of four months, the mean ± SD concentration of copper in the livers of ewes in group C was 234 ± 98 µg/g; of ewes in group M 28 ± 4 µg/g; and of ewes in group MS 26 ± 4 µg/g, whereas in the rams it was 153 ± 31 µg/g in group C, 56 ± 24 µg/g for group M and 26 ± 5 µg/g for group MS. The concentrations of plasma copper in groups M and MS were higher than that of the control group in both the ewes and the rams. In the case of group C, the concentration of TCA-soluble plasma copper represented about 95% of the total plasma copper compared to 65% in the case of groups M and MS. The induced copper deficiency in groups M and MS was characterized by a loss in wool crimp and wool production as well as loss of body mass. Total concentrations of plasma copper may not be a reliable diagnostic index of copper deficiency in sheep in the presence of high concentrations of molybdenum and sulphate in pastures or drinking water. Under these circumstances, liver copper concentration may be regarded as the most accurate index of the copper status of such animals. The supplementation of molybdenum and sulphate did not influence the concentrations of plasma zinc, calcium, magnesium or phosphorus. However, an effective systemic copper deficiency in both the rams and ewes in groups M and MS appeared to be induced by this treatment.