Studies on the specific activities in building materials, the gamma-radiation levels in dwellings, the concentrations of radon and daughters in the air indoors and the concentration of radon in tap water are in progress in Sweden. On basis of these investigations and of the investigation from the beginning of the 1950s, an attempt has been made to show how the radiation doses in dwellings have changed or may be canged by human activities and what these changes imply in terms of collective dose. The annual collective absorbed dose in the basal cells of the critical bronchial region have increased from 11*10**3 manGy for the occupants of dwellings existing in 1950 to 25*10**3 manGy for dwellings existing in 1975. If the building of houses continues as at present it can be estimated that the annual collective dose will be between 25 and 31*10**3 manGy for the dwellings of 1985.