As part of the National Water-Quality Assessment Pro- gram of the U.S. Geological Survey, this study examines the occurrence of nine trace elements in bed sediment of varying mineralogy and land use and assesses the possible effects of these trace elements on aquatic-macroinvertebrate community structure. Samples of bed sediment and macroinvertebrates were collected from 154 streams at sites representative of undeveloped, agricultural, urban, mined, or mixed land-use areas and 12 intermediate-scale ecoregions within the con- terminous western United States, Alaska, and Hawaii from 1992 to 2000. The nine trace elements evaluated during this study-arsenic (As), cadmium (Cd), chromium (Cr), copper (Cu), lead (Pb), mercury (Hg), nickel (Ni), selenium (Se), and zinc (Zn)-were selected on the basis of potential ecologic significance and availability of sediment-quality guidelines.