The dose due to ingestion of mushrooms depends on their radioactive content. However, not all the mass of the mushroom ingested is digested and assimilated completely by man. To analyse the degree of assimilation of the radioactive content of mushrooms, we have carried out culture under controlled laboratory conditions for Pleurotus eryngii mushrooms to which we added known activities of 134Cs, 85Sr and 239Pu. We then applied the Van Soest method to the fruiting bodies, which were obtained in order to determine the fraction of these radionuclides associated with the major components of the cell that are assimilable by man. Finally, on the basis of the results, we determined the dose due to 137Cs, 90Sr and (239+240)Pu for several mushroom species collected in different natural and semi-natural ecosystems in Spain.