Contaminants were measured in the Mississippi River and some of its tributaries between Minneapolis, Minnesota, and the Gulf of Mexico on 10 separate occasions between July 1987 and May 1992. Measurements included contaminants dissolved in the river waters, those adsorbed on sediment particles being transported by the rivers, and contaminants stored in bottom sediments. Data from this study provide a snapshot view of the chemical 'state of the river' circa 1990 that will serve as a baseline against which future changes and trends may be measured in the Nation's largest river.