This Statement was prepared to give you information about chlorinated dibenzofurans (CDFs) and to emphasize the human health effects that may result from exposure to them. The Environmental Protection Agency (EPA) has identified 1.350 hazardous waste sites as the most serious in the nation. These sites comprise the "National Priorities List" (NPL): Those sites which are targeted for long-term federal cleanup activities. CDFs have been found in at least 57 of the sites on the NPL. However, the number of NPL sites evaluated for CDFs is not known. As EPA evaluates more sites, the number of sites at which CDFs is found may increase. This information is important because exposure to CDFs may cause harmful health effects and because these sites are potential or actual sources of human exposure to CDFs.