The chemical composition of streamwater in mountainous regions is mainly influenced by non-point sources. Based on weekly flow proportional samples the inorganic chemistry of streams in the Flyschzone of the northern Prealps is analysed for extreme (95% percentile) concentrations of solutes. It is typical for all 3 basins considered - regardless of size and land use - that mineral concentrations (Ca, Mg, Na, K, Si, S) show maximum levels during low flows. Such hydrologie conditions are most frequent in autumn at the end of prolonged rainfree periods and in winter when freezing temperatures and a nonmelting snowpack prevail. Nitrates and ammonia show peak concentrations during the dormant season and at medium flow rates. Suspended sediment concentrations are highest in mid summer during the times when intensive thundershowers occur. The respective streamflow volumes however are moderate indicating that isolated individual intensive storms yield higher concentrations than prolonged rain events. In order to explain the suggested mechanisms more detailed studies on a storm basis are necessary.