For use in a nationwide geochemical mapping project, 496 stream sediment samples were collected in eastern Japan including the nation's capital, Tokyo. The 51 elements were determined using ICP-AES and ICP-MS; their spatial distribution maps were created using geographic information system (GIS) software. Spatial distribution patterns of elemental concentrations in stream sediments are consistent with the distribution of surface geology. Heavy metals and toxic elements are highly elevated in the sediments associated with mineral occurrences, but their distributions are limited to a small area. Surveying for nationwide geochemical mapping avoids collection of samples near contamination sources. Nevertheless, high concentrations of P (P2O5), Cr, Ni, Cu, Zn, Sn, Sb, Hg, and Pb were found in populated areas. Results of statistical analyses – analysis of variance and a multiple comparison test – suggest that the enrichments are not coincidental phenomena, rather these sediment samples accurately represented contamination.