[en] A method of lung dose calculation is available as described in the UNSCEAR 1982 Report for estimating the human lung dose to radon daughter products in the atmospheric air. By using the method, the effective dose equivalent of the respiratory tract can be calculated from the products of four factors, i.e., radon concentration, the equilibrium factor, the exposure time and the dosimetric coefficient. Many problems or uncertainties, however, are included in the simplified method. They are classified into three categories: (1) items related to measurement - radon and daughter products concentrations in dwellings, ratio of unattached atom to total atom in the atmosphere, size distribution of radioactive aerosol particles in the atmosphere, accuracy and precision of observed values, sampled position and time, and conclusion based on statistics for date, (2) items related to human - occupancy factor, tidal volume, bronchial morphometry, deposition of radioactive aerosol particle, mucociliary clearance rate and location of target cells, and (3) items related to dose calculation - dose conversion factor, quality factor, weighting factor and lung dose model. (author)