Regional deposition of an arbitrary hygroscopic material is estimated by interpolation of deposition efficiencies previously calculated using a hygroscopic particle lung deposition (HPLD) model by Ferron et al. (J. Aerosol Sci., 1988, 19, 611) for spheres of NaCl, ZnSO4· 7H2O and a non-hygroscopic material in the range of 0.1 and 10 μm aerodynamic diameter. The interpolation is performed for the aerodynamic growth factors of the materials for each individual airway generation. A polydisperse size distribution is simulated by using discrete monodisperse fractions. Applying the estimation method to the deposition of monodisperse and polydisperse CoCl2·6H2O particles, deposition differs by less than 13% from the values obtained from the HPLD model. Two modifications of the estimation model are described: one using the equivalent growth factor instead of the aerodynamic growth factor and the other using the deposition efficiencies of NaCl and a non-hygroscopic material instead of the three materials mentioned above. The first modification gives similar results and the second modification gives larger differences up to 20% if compared with the deposition efficiencies obtained with the HPLD model. The estimation method is easier to handle than the HPLD model.