In the near future, Dutch legislation will set an upper limit for thenatural radiation exposure of inhabitants in newly built houses. Therefore,it is necessary to have standardized procedures available for the determinationof the radon exhalation rate of and the activity levels in construction materials.In this paper we describe a method for determination of activity levels inconstruction materials. This method comprises radionuclide-specific calibrationof Marinelli-beaker geometries with a range of material densities. This standardmethod was validated in a round-robin involving 6 laboratories, organizedby two of the authors (M.B. and H.J.G.) of this paper. In this paper, resultsobtained according to the norm are compared with results obtained at IRI witha more elegant but possibly less robust method.