The geochemical properties of a small stream have been studied by repeated sampling of sediment and peat during the period May-September. The element concentrations are time-dependent in the sediments but independent of time in the peat. Detailed sampling shows that one sample represents a section of less than 2 m of the stream. The rapid changes of the element concentrations are mainly caused by changes in the local environment along the stream. The usual sampling distance of 200 m in geochemical surveys is too wide. The elements studied fall into two main groups of different geochemical properties. The elements of one group, e.g. Fe, Mn, Mo and Zn, are enriched in the stream channel by local geochemical processes. The reproducibility of the observations is improved by a normalization to either Fe or Mn. A weak Cu-Mo dissemination is indicated by Mo only after the application of such a normalization procedure. Cu is found to be the most useful element for stream-sediment surveys. The study also shows, however, that the absence of Cu anomalies in a stream does not exclude the existence of a Cu-mineralization.