The Nationwide Urban Runoff Program (NURP) priority pollutant monitoring project was initiated to evaluate the presence, concentrations, and potential water quality impacts of priority pollutants in urban stormwater runoff. From 1980 to 1983, 121 runoff samples were collected from 61 predominately residential and commercial sites across the country and analyzed for 127 of the 129 priority pollutants. Seventy-seven priority pollutants were detected, which included 14 inorganic and 63 organic pollutants. Lead and selenium were the inorganic priority pollutants which could represent a potential risk to humans in undiluted runoff. The organic priority pollutants with this potential were two BHC isomers, both pesticides. Dilution, settling, and other fate processes in receiving waters as well as treatment of water supplies tend to make the risk to humans small. The risk to aquatic life from priority pollutant metals is of more concern. Levels of cadmium, copper, lead, and zinc in undiluted runoff exceeded the EPA 1980 acute criteria for protection of aquatic life by a factor of 2 to 8.