In 1978, the U.S. Geological Survey initiated a 5-year study of the High Plains regional aquifer to provide: (1) Hydrologic information needed to evaluate the effects of continued ground-water development; and (2) computer models to predict aquifer response to changes in ground-water development. The plan of study for the High Plains Regional Aquifer-System Analysis was described by Weeks (1978). A description of the High Plains aquifer and a map of the 1978 water table were presented by Gutentag and Weeks (1980). Maps of the bedrock geology, altitude of aquifer base, and saturated thickness of the High Plains aquifer were published by Weeks and Gutentag (1981). Water-level and saturated-thickness changes, from predevelopment to 1980, were mapped by Luckey, Gutentag, and Weeks (1981). This report describes the areal distribution of dissolved solids and sodium in the water of the High Plains aquifer. Data used in this study were provided by the U.S. Geological Survey and State agencies in each of the eight States in the High Plains. Their contribution is an integral part of this investigation.