Hazard surveillance, the ongoing assessment of chemical use and worker exposure to the chemicals, was presented as a way to supplement occupational disease surveillance. Rankings by Industry Risk Index (IRI), Occupational Safety and Health Administration (OSHA) Weighted Index (OWI), Inspection Based Exposure Rankings (IBER) and employment were generated for industries located in Los Angeles County. Three approaches to prioritizing the exposure rankings were considered: by high employment in Los Angeles County, by high scores on several lists, and by chemical. According to the authors, identifying overlap between ranking systems is useful in choosing industries for initial followup. If an industry appears on the top of several lists it indicates that there is a history of documented overexposures to certain chemicals and of potential exposures to a number of other toxic substances and that a significant number of workers are thought to be exposed. Although there are significant areas of overlap among the three ranking systems, there are also major areas where overlap did not occur. The lack of overlap between the IBER and IRI ranking systems underscores the differences in the data bases on which they rely and the underlying assumptions of each method. The relative utility of the data bases and approaches described also depend on the end use of the data. Where intervention is needed due to high exposures to documented hazards, the OSHA management information system information and the IBER ranking are especially advantageous. In general, epidemiologic research which seeks to establish a new cause effect relationship between a particular health outcome and a work related exposure will be better informed by having the National Occupational Hazard Survey data available.