Natural background characteristics and grazing cattle both influence the chemical and bacteriological quality of pasture runoff in south central Nebraska. The chemical quality of runoff from unstocked grassland was poorer than that from grazed pasture. The chemical quality of pasture runoff, which was better than runoff from cultivated cropland and urban areas, was within recommended water quality criteria. Cattle grazing increased fecal coliform counts 5 to 10 fold, however, rainfall runoff from both grazed and ungrazed pasture exceeded the water quality criterion of 200 organisms per 100 ml more than 90 percent of the time. Recommended bacteriological water quality criteria may be inappropriate for characterizing pasture runoff and other non-point sources of potential pollution.