The National Institute for Occupational Safety and Health (NIOSH) has developed two data files, the Registry of Toxic Effects of Chemical Substances (RTECS) and the National Occupational Hazard Survey (NOHS), which contain data on chemical toxicity and worker exposure to chemicals. A technique for objectively assessing the potential health risk due to chemical exposure in the workplace is described. Computer algorithms used to combine information in NIOSH data files to rank-order chemicals by considering toxicologic properties and number of workers exposed are discussed. Their use in producing indices of the potential health risk encountered by workers in specific industries and occupations arising from chemical exposure are described. Five indices are identified and appropriate algorithms are defined with examples of typical index pages.