The action of Zirconium (Zr) on biological systems presents an enigma. It is ubiquitous, being present in nature in amounts higher than most trace elements. It is taken up by plants from soil and water and accumulated in certain tissues. The entry into animal systems in vivo is related to the mode of exposure and the concentration in the surrounding environment. Retention is initially in soft tissues and then slowly in the bone. The metal is able to cross the blood brain-barrier and is deposited in the brain and the placental barrier to enter milk. Physiologically, it exists as an ion in the body. The daily human uptake has been known to be as high as 125 mg. The level of toxicity has been found to be moderately low, both in histological and cytological studies. The toxic effects induced by very high concentrations are nonspecific in nature. Despite the presence and retention in relatively high quantities in biological systems, Zr has not yet been associated with any specific metabolic function. Very little information is available about its interaction with the compounds of the genetical systems, such as nucleic acids. Apparently, the metal is neither an essential nor toxic element in the conventional sense. However, the increasing exposure to this element through its increasing use in new materials and following radioactive fallout, has increased the importance of the study of its effects on living organisms. The tetravalent nature of the ionic state and the high stability of the compounds formed are important factors that need to be considered, as also the accumulation of this element in the brain, reminiscent of the relationship between Aluminum and Alzheimer's disease. Zirconium is a metallic element with the atomic number 40 and mol wt 91.99, and belongs to the group IVB and second transition series of the fifth period of Mendeleyev's periodic table. It was named from Arabic zargun, meaning gold color. Discovered in the semiprecious gem zircon, as orthosilicate, by Klaproth in 1789, Zr was isolated as an element by Berzelius in 1824. In its metal form, Zr is hard and resistant to corrosion, heat, and acid. Zirconium behaves like an essential trace metal in the biosphere, although the possibility that it is a natural contaminant with no considerable physiological effects must be considered (PMID: 1283692, Biol Trace Elem Res. 1992 Dec;35(3):247-71.).