Although consequences of zinc deficiency have been recognized for many years, it is only recently that attention has been directed to the potential consequences of excessive zinc intake. This is a review of the literature on manifestations of toxicity at several levels of zinc intake. Zinc is considered to be relatively nontoxic, particularly if taken orally. However, manifestations of overt toxicity symptoms (nausea, vomiting, epigastric pain, lethargy, and fatigue) will occur with extremely high zinc intakes. At low intakes, but at amounts well in excess of the Recommended Dietary Allowance (RDA) (100-300 mg Zn/d vs an RDA of 15 mg Zn/d), evidence of induced copper deficiency with attendant symptoms of anemia and neutropenia, as well as impaired immune function and adverse effects on the ratio of low-density-lipoprotein to high-density-lipoprotein (LDL/HDL) cholesterol have been reported. Even lower levels of zinc supplementation, closer in amount to the RDA, have been suggested to interfere with the utilization of copper and iron and to adversely affect HDL cholesterol concentrations. Individuals using zinc supplements should be aware of the possible complications attendant to their use.