Zinc, copper and iron levels of tissues in rats or beagle dogs were measured after a 13- or 52-week toxicity study of polaprezinc, which contains a zinc element. The zinc content in almost all rat tissues remarkably increased with a conspicuous decrease of copper and various changes of iron at doses of 600 mg/kg/day or more. Zinc and copper levels increased and decreased respectively, at 300 mg/kg/day. At a dose of 150 mg/kg/day, there was a slight increase of zinc in some tissues at 52-weeks, but no copper decrease. The results obtained from beagle dogs differed somewhat from that in rats. Dogs treated with polaprezinc at 50 mg/kg/day or more accumulated zinc in some tissues. A copper decrement was seen only in the liver and heart from the group given 300 mg/kg/day, whereas copper levels in the kidney of all treated groups were higher than that in the control, suggesting that canine polaprezinc toxicity is due to direct zinc toxic effects.