[en] Knowledge of the radiation burden from natural sources to man in his normal environment is of great importance in our time. However, it is not sufficient to estimate only the average dose for a large population; it is desirable to know the dose to all organs and tissues with high radiation sensitivity for different groups of the population. Knowledge of such a dose distribution pattern for various population groups would enable future epidemiological studies to be carried out on possible biological effects due to low-level irradiation. The following components have to be investigated: (1) Cosmic rays. (2) External radiation from subsoil, building materials and air. These measurements should be carried out not only outdoors, but mainly in living, working and sleeping rooms. (3) Content in the air of ²²²Rn, ²²⁰Rn and their short- and long-lived decay products, both outdoors and indoors. This component causes the largest radiation burden from natural radioactivity to some tissues. These measurements are complicated by the fact that indoors and outdoors there are not only large local variations (up to a factor 300) but also temporal fluctuations at the single sites up to a factor 10. A suitable method for obtaining temporal significant means from grab-sampling is presented. (4) Radioactivity of drinking water and food. With these results the frequency distribution of the mean dose values in different organs for groups of a given population can be calculated. The statistical treatment of the data and the necessity to consider additional parameters about the population are discussed. (author)