A trial was conducted in which the rations of sheep were supplemented with different levels of Cu and Mo. The S intake was kept constant at 2,1 g/sheep/day. Two levels of Mo were fed, viz. 38 mg/sheep/day for 92 days or 21 mg/sheep/day for 182 days. Each Mo group was subdivided into three Cu treatments, viz. 24, 40 and 68 mg Cu/sheep/day. No difference in Cu accumulation in the livers was observed between the different levels of dietary Mo. A linear increase in hepatic Cu content was recorded, depending on total Cu intake and independent of duration of Cu feeding. Between 1,18 and 1,97% of the Cu taken in, was retained in the livers. Indications of the existence of interactions between Cu and Fe and between Cu and Zn were obtained from Fe and Zn concentrations in the livers. Although total Mo intakes during the experimental periods were approximately the same, Mo concentrations in the livers, kidney cortices and plasma were significantly higher (P < 0,01) at a Mo intake of 38 mg/sheep/day than at 21 mg Mo/day. It was concluded that Mo concentrations in these body tissues are of a fairly transient nature, being related, at a constant S intake, not to total intake of Mo but to the daily amount of Mo consumed.