Rhenium (Re, also known as NSC-600662) is a chemical element that was discovered in 1925. It is one of the scarcest elements on earth. This metal has a silvery-white color, high density, and high melting point. It is part of an alloy used to make X-ray tubes and rotating X-ray anodes, because the addition of rhenium prevents crazing of the anode surface. Apart from this medical application, rhenium is also used in plating, jewelry, igniters for flash bulbs, electrodes, thermocouples, electrical contacts, components for missiles, and other products and equipment. Its toxicity has been insufficiently studied, but exposure may cause health problems such as respiratory problems, skin and eye irritation, and burns. Also, more research is needed on environmental effects of rhenium.