The uptake and transfer of natural radionuclides, other than (40)K, from soil to mushrooms has been somewhat overlooked in the literature. Their contribution to the dose due to the consumption of mushrooms was considered negligible. But the contribution of (210)Pb in areas unaffected by any recent radioactive fallout has been found to be significant, up to 35% of the annual dose commitment in Spain. More than 30 species of mushrooms were analyzed, and the (210)Pb detected was in the range of 0.75-202 Bq/kg d.w. A slight difference was observed between species with different nutritional mechanisms (saprophytes > or = mycorrhizae). The (210)Pb content was correlated with the stable lead content, but not with its predecessor in the uranium radioactive series, (226)Ra. This suggested that (210)Pb was taken up from the soil by the same pathway as stable lead. The bioavailability of (210)Pb in soil was determined by means of a sequential extraction procedure (NH(4)OAc, 1M HCl, 6M HCl, and residue). About 30% of the (210)Pb present in the soil was available for transfer to mushrooms, more than other natural radionuclides in the same ecosystem. Lycoperdon perlatum, Hebeloma cylindrosporum, and Amanita curtipes presented the highest values of the available transfer factor, ATF. As reflected in their ATF values, the transfer from soil to mushroom of some natural and anthropogenic radionuclides was in the following order: