Maximum concentrations of toxic metals in human food have been established for cadmium and lead independently, but both metals may be increased concurrently in sewage sludge and other forms of industrial pollution. Synergism exists between the two metals in their toxic effects (Kaji et al., 1995), which emphasises that the toxic thresholds cannot be prescribed for metals in isolation. An experiment was conducted that investigated the medium and long-term effects of adding lead to the diet of sheep, to determine whether the animal's metabolism would adapt to alter the effects of lead on the accumulation of other toxic metals.