To estimate chemical occupational health risk for an employee, a computer system has been developed using a three step process: access the relative toxicity of the chemicals to which the workers are exposed; examine the national incidence of exposure to these chemicals and the working conditions under which workers come into contact with these chemicals; and determine an estimate of the risk to health arising from multiple chemical exposures as they are associated with various groups of workers. As it is presently operating, the computer system permits three basic outputs: the Hazard Risk Index, which is a rank order listing of 1721 chemicals arranged by relative toxicity and user weighting of health effects; an Adjusted Hazard Risk Index, which is a rank ordered listing of chemicals using toxicological data and working conditions, including potentials for exposure; and the Industrial Risk Index, which is an industry listing rank ordered by potential health risk. The data bases from which information has been drawn for this system include the National Occupational Hazard Survey and the Registry of Toxic Effects of Chemical Substances. One way to test the functioning of the system is to compare its ranking of occupational groups to results obtained from many epidemiological studies conducted in recent years. The output obtained from the model is very much dependent on the decisions made by the operators in establishing the data by setting health effects weights, selecting tumorigenic options, and using census data. However, even with these limitations, the model has several possibilities which make it a research tool of great versatility.