Abstract: Eighty-five stream sites in and near the six-county Greater Pittsburgh Region were sampled in mid-June 1971 and again in mid-October 1972. Concentrations of inorganic nitrogen, organic carbon, or phosphorus were high enough to indicate potential problems at about a quarter of the sampling sites. Temperature, dissolved oxygen, and pH values indicated a generally favorable capacity for recovery from degradation, although a number of streams east of the Allegheny and Monongahela Rivers are marginal or lacking. Regionally, sulfate is the dominant ion and was observed in concentrations of 40 milligrams per liter or more at 90 percent of the sites. Bicarbonate exceeded 100 milligrams per liter at 22 sites. A moderate to high degree of mineralization is indicated by conductance readings of more than 500 micromhos per centimeter at half of the sampling sites.