The potassium content of 410 species (1075 samples) of wild mushrooms ranged between 1.5 and 117g/kg dry wt. It was dependent on species and genus, and on the average was highest in Coprinaceae and lowest in Polyporaceae. A positive correlation was observed between potassium and water content; consequently, the potassium content of the wet wt. showed less variation: it ranged between 0.6 and 14.6 g/kg. In the solid matter of single fruit-bodies (11 species) potassium was distributed as follows: flesh of the cap greater than stem greater than gills or tubes greater than spores. The flesh of the cap contained maximally 1.8 times the potassium of the gills. But due to a correspondingly higher water content, significant potassium differences between fresh weights of these parts of fruit-bodies were uncommon. Potassium was concentrated 20--40-fold in fruit-bodies as compared with the soil.--According to our results mushrooms rank among the most potassium-rich vegetables, appropriate for consideration in diets in chronic potassium deficiency. On the other hand, toxic effects must be considered, especially in cases of renal insufficiency.