Concern over the presence of contaminants of emerg-ing concern, such as pharmaceutical compounds, hormones, and organic wastewater compounds (OWCs), in waters of the United States and elsewhere is growing. Laboratory tech-niques developed within the last decade or new techniques currently under development within the U.S. Geological Sur-vey now allow these compounds to be measured at concentra-tions in nanograms per liter. These new laboratory techniques were used in a reconnaissance study conducted by the U.S. Geological Survey, in cooperation with the Pennsylvania Department of Environmental Protection, to determine the occurrence of contaminants of emerging concern in streams, streambed sediment, and groundwater of Pennsylvania. Com-pounds analyzed for in the study are pharmaceuticals (human and veterinary drugs), hormones (natural and synthetic), and OWCs (detergents, fragrances, pesticides, industrial com-pounds, disinfectants, polycyclic aromatic hydrocarbons, fire retardants and plasticizers).