Methods are described for low-level Po210 and Pb210 analysis of amounts up to 1 l. volume of urine, 10–20 g of bone, 50–60 g tissue. The methods are applied to the analysis of experimental animals exposed to natural levels of radon and its short-lived daughters, yielding a natural Po whole body content of about 5 × 10-15 c/g. When the experimental animals are exposed to elevated daughter-free radon atmospheres, the Po and Pb body contents are increased. The study is part of a program to explore the usefulness of measurement of the Po content of miners' urine as an indicator of the integrated dose from radon and its daughters.