Abstract 1. Cultivation of Pleurotus ostreatus on cadmium-enriched substrates always implies a significant increase of copper together with cadmium in fruit bodies. 2. In fruits, cadmium accumulates in the subcellular cytosoluble fraction, according to exposure dose; also copper mainly accumulates in the cytosol. 3. Cadmium and copper are mainly bound to components weighing 3500 and 6000 D in different percentages according to exposure dose: both of these proteins are present in the control as copper-chelating compounds. 4. Amino acid analysis reveals many similarities between these components, with higher amounts of: aspartic acid (15%), glutamic acid (10–13%), cysteine (8.5–10%), glycine (10%). 5. Zinc is excluded from these interactions; its homeostasis is, however, affected by cadmium exposure.