Concentrations of elements in streamwater were monitored in 57 watersheds located along elevational and successional gradients in the White Mountains of New Hampshire, USA. Concentrations of C1— and SO4– decreased with increasing elevation as a result of differences in relative evapotranspiration along the elevation gradient. Concentration of Na+, Ca++, and Mg++ also decreased with increasing elevation, but with a steeper slope. Rock weathering/unit of water flux as well as relative evapotranspiration controls concentrations of these cations. Potassium and NO3— concentrations were highly variable, both seasonally within a stream and among streams. Differences among watersheds in terms of successional status are important in controlling NO3— and K+ concentrations. Streams draining old—aged forested ecosystems had higher concentrations of NO3—, K+, and other plant nutrients than did streams draining intermediate—aged successional ecosystems at the same elevation. Nine spruce—fir watersheds which have no record of logging or other extensive human disturbance had streamwater NO3— concentrations averaging 53 microequivalents/litre, while five other spruce—fir watersheds which had been logged 30 yr previously had streamwater NO3— concentrations averaging 8 meq/1. The major factors controlling streamwater concentrations of elements in these watersheds are factors related to supply (precipitation chemistry, relative evapotranspiration, rock weathering) and to plant accumulation of nutrients. Rapidly—growing successional ecosystems can accumulate a large fraction of inputs of nutrient elements, particularly during the growing season. Steady state ecosystems, those with no net biomass accumulation, have nutrient outputs equal to nutrient inputs. The increased losses of nutrient elements from clearcut watersheds in New Hampshire can be explained in these terms. Clearcut or otherwise disturbed ecosystems may have mineralization in excess of plant uptake, leading to element outputs in excess of inputs. Field experiments demonstrated that the prevention of plant uptake by root trenching led to soil NO3— concentrations comparable to those observed in streamwater in the clearcut watershed at Hubbard Brook Experimental Forest.