Using quantitative risk assessment (QRA) for occupational exposure limit (OEL) setting was discussed. The regulatory aspects of NIOSH and OSHA OELs were considered. The OSHA OELs, known as permissible exposure limits (PELs) are enforceable standards which employers are required to comply with under penalties prescribed by law. NIOSH standards, known as recommended exposure limits (RELs), which are not enforceable, are based on qualitative and quantitative assessments of a health based risk. In the case of qualitative risk assessments, the analysis is combined with expert judgments to form a coherent, scientific basis in support of the limit. It was noted that a QRA will not produce an estimate of zero risk since exposure at any level will always be associated with some degree of risk. A survey of lifetime risks of cancer from various agents indicates that excess risks exist for some exposures that are regulated. The philosophy of the NIOSH QRA program was discussed. NIOSH, whenever possible, prefers to use epidemiological rather than experimental animal data to develop QRAs. NIOSH also uses the best available methods and generally utilizes several different models to evaluate dose response relationships. QRAs recently completed by NIOSH included an assessment of the lung cancer risk presented by radon daughters, diesel exhaust emissions, and cadmium (7440439). The QRA for radon daughters served as the basis for an REL in the NIOSH criteria document for radon daughters.