[en] The results are described of recent observations at Argonne National Laboratory, contributing to our knowledge of such factors as the origin of high levels of radon in houses, its variability with time or otherwise, its uniformity throughout the house or otherwise, and the behavior and fate of the short-lived daughter-products. In a sample of 110 houses, mostly in the west suburban area of Chicago, 15% had radon concentrations in excess of 6 pCi litre^-₁ and 96% greater than 10 pCi litre ^-₁. If this distribution is representative of all houses in the USA, the population being exposed to such high concentrations of radon is far greater than the number of people in Grand Junction being exposed to quite similar concentrations from technologically enhanced radioactivity. There is a great need for far more extensive data on radon in houses