[en] Two different methods for the measurement of airborne radon daughters have been developed and applied to various environments. The relative deposition of radon daughters in dwellings is found to be of the same size as in mines, and the deposition in children to be as large as in adults or even larger. This is in accordance with the theoretical calculations which result in higher doses to children than for grown ups. The verification of existing models of deposition and retention of inhaled radon daughters is proceeding. (G.B.)