ZusammenfassungFourteen European forest soils from the boreal to the mediterranean climate on different parent materials were investigated with respect to their ability to store NH4+ in exchangeable form, using sorption isotherms. Distribution coeflicients for NH4' sorption per unit weight of soil were in the range of 0.02 to 0.77. NH4+ sorption coemcients were usually highest in the forest floor of a given soil.NH4' sorption behaviour of mineral soil horizons was correlated to soil parameters that are determined during routine soil analysis. A combination of CEC and base saturation explained up to 95% of the variability of NH4+ sorption. In the forest floors, variability in NH4+ sorption could not be explained quantitatively from independent soil parameters. The affinity of the sorption sites for NH,' was the most important factor for explanation of the variability in NH4+ sorption in the forest floors but was of low importance in mineral soil horizons.As NH4' exchanges predominantly base cations, susceptibility of NH4+ to transport through the soil profile increases with low base saturation of a soil as well as with low CEC values.