This report presents the criteria and the recommended standard based thereon which were prepared to meet the need for preventing impairment of health from occupational exposure to inorganic nickel. The criteria document fulfills the responsibility of the Secretary of Health, Education, and Welfare under Section 20(a)(3) of the Occupational Safety and Health Act of 1970 to ". . .develop criteria dealing with toxic materials and harmful physical agents and substances which will describe...exposure levels at which no employee will suffer impaired health or functional capacities or diminished life expectancy as a result of his work " experience. The National Institute for Occupational Safety and Health (NIOSH), after a review of data and consultation with others, formalized a system for the development of criteria upon which standards can be established to protect the health and to provide for the safety of employees exposed to hazardous chemical and physical agents. The criteria and recommended standard should enable management and labor to develop better engineering controls and more healthful work practices and should not be used as a final goal. These criteria for a standard for inorganic nickel are part of a continuing series of criteria developed by NIOSH. The proposed standard applies to the processing, manufacture, and use of inorganic nickel as applicable under the Occupational Safety and Health Act of 1970. The standard was not designed for the population-at-large, and any extrapolation beyond occupational exposures is not warranted. The standard is intended to (1) protect against injury from inorganic nickel, (2) be measurable by techniques that are valid, reproducible, and available to industry and official agencies, and (3) be attainable with existing technology. However, it will only substantially reduce the risk of developing nickel-related cancers and minimize the risk of developing dermatitis. Ingestion and inhalation of, and dermal exposure to, nickel are common, since nickel is present in air, soil, water, food, and household objects. Although nickel is commonly found in the air, it is present in higher concentrations where there is environmental pollution as a result of the burning of fossil fuels or the processing of nickel. The recommended standard for inorganic nickel is based on the conclusion that these substances are carcinogenic. An excess number of deaths from lung cancer and nasal cancer has been observed in nickel refinery workers. After review of the relevant data, it was concluded that a substantial portion of those excess deaths was caused by exposure to airborne nickel compounds. It might be reasoned from the limited animal data that only nickel subsulfide is a carcinogen; or the interpretation might be made, based on some epidemiologic studies. that only one stage of nickel refining presents a risk of cancer. In addition, it might be concluded from limited data on human exposures and environmental concentrations that the safe threshold level of exposure to nickel compounds is greater than the recommended environmental limit. Should sufficient evidence be developed to demonstrate that any of these is a correct interpretation or that some nickel compounds are not carcinogenic, the recommended standard for inorganic nickel will be considered for revision. The available evidence indicates that workers can be adversely affected by skin contact with nickel, particularly when it is in solution. Because of the ubiquity of nickel in the nonoccupational environment, some individuals may develop a sensitivity to nickel regardless of precautions taken in the workplace. The standard cannot protect these individuals from developing recurrent dermatitis when occupationally exposed to inorganic nickel. However, it will greatly reduce the risk of unsensitized workers becoming sensitive to nickel in the course of their employment. Even though there is considerable information about occupational health problems associated with inorganic nickel, several major areas require further research. Epidemiologic studies are needed to determine the risk of developing nickel-related cancers in occupations which have not been adequately studied, eg, welding, plating, and refining nickel oxide ore; inhalation experiments in suitable animal species are needed to supplement these studies. Both animal and human studies are needed to ascertain whether the limited information on reproductive effects has any relevance to human exposure. Animal studies are needed to characterize the acute and chronic toxicities of the many nickel compounds for which insufficient information is available. The health effects of occupational exposure to nickel carbonyl are not discussed in this document, nor have the effects of simultaneous exposure to nickel and cadmium been reviewed herein. The effects ,of nickel carbonyl are discussed in "Special Occupational Hazards Review and Control Recommendations for Nickel Carbonyl" and the effects of cadmium are discussed in the "Criteria for a Recommended Standard--Occupational Exposure to Cadmium." Two other reviews of nickel provide additional information on its toxicity. The International Agency for Research on Cancer (IARC) prepared monographs on nickel and nickel compounds in 1973  and 1976 , in which evidence for the carcinogenicity of all nickel compounds was considered. The Committee on Medical and Biologic Effects of Environmental Pollutants of the National Academy of Sciences published in 1975 a comprehensive review (NAS-NRC report)  of nickel which also included nickel carbonyl.