An investigation was made of the effects of atmospheric effluents from a large urban-industrial area (St. Louis, Missouri) on the water quality in 2 small basins that are frequently downwind of the city. Analyses were made of the relative magnitude of the atmospheric contribution to streamwater pollution, and how this contribution is related to weather conditions. Field sampling was done during a 15 mo. period, and investigation made of atmospheric-streamwater relationships for storm, seasonal and annual periods. Computations were made for 12 chemical constitutents in the rainwater and streamwater. Only minor changes usually occur in streamwater pollutant concentrations during and shortly following storms, and no strong relationship exists between streamwater concentration and weather conditions. For most pollutants the atmospheric deposition was small compared with the annual stream load because of major surface sources. Evidence was also found that urban-industrial sources can occasionally be important contributors to stream contamination.