The Reston Chlorofluorocarbon Laboratory of the U.S. Geological Survey was established in 1994 to provide analytical services for determination of the chlorofluorocarbons (CFCs) CFC-11, CFC-12, and CFC-113 in air and water samples. Currently the laboratory provides analytical services for CFCs, sulfur hexafluoride, dissolved gases including nitrogen, argon, methane, carbon dioxide, oxygen, and helium, and administers the USGS contract for tritium/helium-3 dating. The data generated by the Reston Chlorofluorocarbon Laboratory are being used in hydrologic studies to trace the flow of young water (0- to 50-year time scale) and to determine the time elapsed since recharge (ground-water age). The laboratory supports research applications of environmental tracers in hydrologic studies conducted by the U.S. Geological Survey. It is managed under the direction of L. Niel Plummer and Eurybiades Busenberg of the National Research Program, Water Resources Division, and is located in the USGS Headquarters in Reston, Virginia.