Individual dose factors for the inhalation of Rn and its daughter products were calculated for environmental dose assessments. An activity median aerodynamic diameter of 0.1 .mu.m was used. The dose to an individual was calculated by multiplying the estimated intake from inhalation for a particular radionuclide by the corresponding dose factor. A working level month-to-dose conversion factor was 1 rad/WLM [working level months] to the epithelial tissue of the tracheobronchial region, assuming 100% daughter equilibrium and 10% free 218Po ions.