The radon concentrations in indoor air and in soil air vary both on short term (daily, weekly) and onlong term (seasonal). The radon level and its changes depend on a few parameters, which may bedifferent from one building to another and from one type of soil to another. It is important to know theseasonal variation of the indoor radon levels if the level is to be compared with the national upperlimits in Europe for indoor radon concentrations.