Editors' Summary: One of the most important participants in the Superfund scheme is the Agency for Toxic Substances and Disease Registry. Established in 1980 pursuant to CERCLA, the ATSDR evaluates the potential health problems caused by individual NPL sites and analyzes the health effects of numerous substances subject to Superfund cleanup. Dr. Johnson, Associate Administrator of the ATSDR, describes his agency's various functions, its plans for future activities, and how it is adapting traditional public health methods of disease prevention and control to meet the unique challenge posed by hazardous substances in the environment.