Annual loads to the Great Lakes from U.S. tributaries were estimated for total phosphorus, soluble ortho phosphorus, suspended solids, total nitrogen, nitrate nitrogen, ammonia nitrogen, and chloride. Loads were calculated for water years 1975 and 1976 using all available data. All loads for monitored tributaries were calculated using the ratio-estimator calculation method except for Lake Erie tributary loads which were obtained from the Lake Erie Wastewater Management Study. In order to provide complete coverage of the basin, loads from unmonitored watersheds were estimated from unit loads determined from similar and usually adjacent monitored watersheds. Municipal and industrial point sources discharging to U.S. Great Lakes tributaries were inventoried and their loading contribution estimated.