When the U.S. Congress passed the Occupational Safety and Health Act of 1970 (Public Law 91-596), it established the National Institute for Occupational Safety and Health (NIOSH). Through the Act, Congress charged NIOSH with recommending occupational safety and health standards and describing exposure levels that are safe for various periods of employment, including but not limited to the exposures at which no worker will suffer diminished health, functional capacity, or life expectancy because of his or her work experience. Criteria documents contain a critical review of the scientific and technical information about the prevalence of hazards, the existence of safety and health risks, and the adequacy of control methods. By means of criteria documents, NIOSH communicates these recommended standards to regulatory agencies, including the Occupational Safety and Health Administration (OSHA), health professionals in academic institutions, industry, organized labor, public interest groups, and others in the occupational safety and health community. This criteria document is derived from the NIOSH evaluation of critical health effects studies of occupational exposure to hexavalent chromium (Cr VI]) compounds. It provides recommendations for controlling workplace exposures including a revised recommended exposure limit (REL) derived using current quantitative risk assessment methodology on human health effects data. Cr(VI) compounds include a large group of chemicals with varying chemical properties, uses, and workplace exposures. Their properties include corrosion-resistance, durability, and hardness. Sodium dichromate is the most common chromium chemical from which other Cr(VI) compounds may be produced. Materials containing Cr(VI) include various paint and primer pigments, graphic art supplies, fungicides, corrosion inhibitors, and wood preservatives. Some of the industries in which the largest numbers of workers are exposed to high concentrations of Cr(VI) compounds include electroplating, welding, and painting. An estimated 558,000 U.S. workers are exposed to airborne Cr(VI) compounds in the workplace.