Estimating the potential health risk encountered by workers due to their exposure to various chemicals is enormously complex, since many chemicals be involved and each may have multiple toxic effects. As an aid to this estimation process, a computer program, or model, which computes index numbers expressing the relative health risk of occupational groups due to their potential chemical exposures was developed at the National Institute for Occupational Safety and Health (NIOSH). This model considers an inventory of the chemicals to which specific occupational groups are potentially exposed, the published information regarding the toxic effects of each chemical, and the conditions of occupational exposure. The system then develops indices of potential occupational group health risk by considering weighted combinations of eight distinct health effects. No direct comparison with external occupational risk indices is currently possible, but internal testing of the model reveals no obvious inconsistencies.