We have reviewed existing data sources available for conducting hazard surveillance. Both the NIOSH NOHS/NOES and the OSHA IMIS can have significant value for hazard surveillance that is designed both to establish priorities for various preventive strategies--including intervention, research, and planning--and to complement disease surveillance. These systems also have certain limitations that affect their overall value in these regards. We have proposed alternative hazard surveillance systems that would expand the database on actual exposures in the workplace by requiring that industry systematically conduct environmental monitoring for defined substances and then provide the data to OSHA and NIOSH for use in hazard surveillance.