Excretion rates of Po-210 and Pb-210 in the urine were investigated in 40 healthy inhabitants of Prague (22 males, 18 females, age: 2370 y, non-smokers). In 20 inhabitants the excretion rates of Po-210 and Pb-210 in faeces were also studied. The mean urinary excretion rates of Po-210 and Pb-210 were 4.1 and 6.0 mBq d(1), respectively. It was demonstrated, statistically, that the urinary excretion rates of Po-210 and Pb-210 are higher in men than those in women. The highest excretion rates of Po-210 and Pb-210 found in the participants were 10.8 and 16.6 mBq d(1), respectively. The mean activity ratio of Po-210/Pb-210 in the urine was 0.73. The mean excretion rates of Po-210 and Pb-210 in faeces were 56.5 and 54.6 mBq d(1). The mean activity ratio of Po-210/Pb-210 in faeces was 1.0.