The accumulation and retention of copper (Cu) in the livers of Ile de France and South African Mutton Merino lambs were compared at four levels of dietary molybdenum (Mo) supplementation, viz. 0, 2, 4 and 8 mg Mo/ lamb/day in a 2 x 4 factorial experiment. Individual lambs consumed an average of 36,3 mg Cu and 3,7 g sulphur per day. The accumulation of Cu and Mo in the kidney cortices and in the livers of the lambs was measured. At each level of Mo intake the lie de France accumulated and retained more (59,8% P<0,01) dietary Cu in their livers than the Mutton Merinos. In the a Mo treatment the lie de France retained 1,96% of their dietary Cu in their livers and the Mutton Merinos 1,30% (P<0,01); at the 2 Mo level 1,64% vs 1,04% (P<0,05); at 4 Mo 0,77% vs 0,40% (P>0,05) and at 8 Mo intake 0,25% vs 0,16% (P>0,05) respectively. The slopes of the regressions depicting Mo intake vs percentage hepatic Cu retention were not significantly different between the two breeds. Significant (P<0,05) increases in kidney cortex Cu and Mo, liver Mo and plasma Cu concentrations were observed at the 8 mg Mo intake above the other Mo treatments although no breed effect was observed.