This pilot study presents preliminary results on interrelations between alkali and alkaline earth elements during their transfer to mycelium and fruitbodies of saprophytic fungi. The accumulation and distribution of four elements (cesium, potassium, sodium, and calcium) was evaluated in king oyster mushroom (Pleurotus eryngii) cultivated under controlled conditions. Elemental composition of caps, stipes, and the substrate was analyzed by atomic absorption/emission spectroscopy to evaluate discrimination, concentration, and transfer factors. The transfer factors determined for all the investigated elements were different and can be put in the following order: Cs > K > Na > Ca. There has been a higher accumulation of cesium in caps than in stipes. Distribution of cesium in fruitbodies depended on the presence of other ions in the substrate. The addition of Ca2+ limited the transport of cesium and potassium from stipes to caps. Sodium and calcium were mainly accumulated in the stipes. In a control experiment, without supplementation with K+, Na+, and Ca2+, approximately 62% of the cesium present in the substrate was extracted by mycelium and transported to the fruitbodies. Possible applications of fruiting saprophytic fungi in bioremediation are discussed.