Polychlorinated biphenyls (PCBs) are synthetic chemicals that were manufactured in the United States between about 1930 and 1977 for use in various industrial and commercial applications because of their nonflammability, chemical stability, high boiling point, and electrical insulation properties (ATSDR, 2000). PCBs were used in numerous products and processes, including electrical, heat transfer, and hydraulic equipment; as plasticizers in various products; in paints and finishes; in pigments, dyes, and carbonless copy paper; and in other industrial and commercial applications. Most of the PCB mixtures manufactured for commercial use in the United States are known by the trade name Aroclor. Each specific Aroclor contained mixtures of some of the 209 congeners, with chlorine contents of the different Aroclors ranging from 21% to 68%. Between 1957 and 1971, 12 types of Aroclors were produced (ATSDR, 2000). During this time, PCBs were used in completely closed systems (such as transformers and capacitors), nominally closed systems (such as hydraulic systems and vacuum pumps), and open systems (such as plasticizers and paints). In 1970, the manufacturer discontinued use of Aroclors in open products and uses that could lead to direct transfer into the environment (Erickson, 1997). Manufacture of PCBs was banned in the United States by Congress, and their use was phased out, except for certain limited uses, by 1978 because of evidence they are persistent in the environment and can cause harmful health effects. PCBs have been shown to cause cancer in animals, and, in chronic animal studies, PCBs have been shown to cause effects on the immune, reproductive, nervous, and endocrine systems. In some studies, exposure to PCBs has been associated with adverse health effects in humans. Because of potential neurotoxic and endocrine effects, there is concern regarding children's exposures to PCBs. Of particular concern is the potential for school children's exposures to PCBs in older schools. Schools constructed between 1950 and 1978 may contain caulk that incorporated PCBs as a plasticizer. Research on sources of PCBs and levels in school environments is needed to improve risk management decisions. To better understand the significance of PCB-contaminated caulk as a source of exposures to children, teachers, and staff in school buildings, the U.S. Environment Protection Agency's (EPA's) Office of Research and Development (ORD) plans to: (1) characterize PCB-contaminated caulk and other potential sources of PCBs in schools; (2) investigate relationships between PCB concentrations in air, on surfaces, and in dust and soil with potential sources in school buildings; (3) evaluate which routes of exposure (e.g., inhalation, contact with surfaces or dust) are likely to be most important; (4) improve exposure assessment models for school-related exposures and examine the feasibility for development of an indoor model for PCBs; and (5) provide samples, data, and other information to assist in developing risk management practices for reducing exposure to PCBs in schools. To meet these research objectives, the ORD National Exposure Research Laboratory (NERL) plans to conduct a measurement study in up to nine schools in the United States. The research described in this study design is being coordinated with research efforts in the ORD National Risk Management Research Laboratory (NRMRL) that are aimed at evaluating PCB emission rates, transport, and exposure mitigation methods. Study Summary Information for Schools is appended. (Contains 9 tables.)