The U.S. Geological Survey requested that the National Research Council review and provide guidance on the direction and priorities of the National Water Quality Assessment (NAWQA) Program. This initial letter report concerns the scientific priorities of the NAWQA program as expressed in its NAWQA Science Framework, assessing whether the framework sets forth adequately the priorities for the future which will be addressed in the third cycle of the NAWQA program. This letter report includes guidance on the nature and priorities of current and future water quality issues that will confront the Nation over the next 10-15 years.