The predominate atmospheric forms of nickel are as sulfate, oxides, and complex oxides. Nickel also occurs in ambient and drinking water and soils. Routes of intake for man are inhalation, ingestion, and percutaneous absorption. Pulmonary absorption varies according to chemical and physical form of the compound. While gastrointestinal intake ranges from 300 to 500 [mu]g daily, absorption is only one to ten percent of intake. Percutaneous absorption, usually through contact with nickel alloys in the household, is related to hypersensitivity and skin disorders. In haled nickel compounds lead to highest levels in lung, brain, kidney and liver. Nickel exposure produces chronic dermatological, respiratory, endocrine and cardiovascular effects. Reproductive and developmental effects have been found in animals but not humans. Various nickel compounds have been tested for mutagenicity, demonstrating the ability of nickel compounds to produce genotoxic effects; the translation of these effects into actual mutations is still not clearly understood. There is evidence both in humans and animals for the carcinogenicity of nickel in some forms. Lifetime cancer risks for continuous inhalation exposure at 1 [mu]g nickel/mp3s have been estimated for nickel refinery dust and nickel subsulfide. There is a growing evidence that nickel may be an essential element for humans.