The accumulation of copper (Cu) in the liver of intensively fed sheep, resulting in sub-clinical organ damage and eventually death due to Cu poisoning, is an important constraint on intensive animal production. Previous studies have demonstrated the antagonistic effect of dietary molybdenum (Mo) on Cu absorption in the ruminant (Suttle, 1991). The role of rumen ciliate protozoa in the breakdown of soluble protein and liberation of sulphide, also a Cu antagonist, and the reporting of a number of cases of chronic Cu poisoning in defaunated animals suggests that the state of the rumen microbial population may also have an effect on the absorption of dietary Cu. The aim of this experiment was to assess the effect of adding Mo to the diet and the availability of straw bedding, (through its effect on rumen environment and microbial population), on the liver Cu concentration at slaughter of early weaned lambs finished intensively on an all concentrate diet.