In this editorial, two distinct objectives were noted which inspire hazard surveillance activities: one, the location and monitoring of groups of workers exposed to agents known to have adverse health effects; and the other, to discover previously unrecognized relationships between exposure and disease. Certain diseases are already clearly associated with occupational exposures and the purpose of hazard surveillance in these cases is confined in the main to locating occupational groups exposed to known causatives so that controls over their exposures may be implemented. Similarly, there are several occupational hazards understood to increase the risk of certain diseases. There is, however, the enormous area where problems arise from simply the vast array of chemical, physical, and biologic agents in the workplaces of the nation to which workers are exposed. Many chemicals arrive at the worksite in formulated products, often with the initial ingredients obscured by trade names, common names, or ambiguous terms, further complicating the problem. Reliance is often placed on the Standard Industrial Classification (SIC) scheme to assign facilities to an industry group. However, this system was not designed to classify industries on the basis of common exposures to hazardous materials. A high degree of variability may lie between facilities sharing an SIC code.