Zinc is a trace element important to bone mineralization as well as, in general, nutrition. It is known that cholecalciferol (vitamin D3) affects bone metabolism. In this study, toxic doses of vitamin D3 were injected subcutaneously (25 mug/d) to rats for 5 wk. It caused a significant increase in serum zinc levels (p < 0.02). On the other hand, no significant increase was detected in the other groups. Excessive amounts of vitamin D3 caused bone breakdown and increased the levels of zinc in blood.