IN THE CASE of internally deposited radionuclides, direct ……measurement of the energy absorbed from ionizing radiation emitted by the decaying of these radionuclides is rarely, if ever, possible. Therefore, one must rely on dosimetric models to obtain estimates of the spatial and temporal patterns of energy deposition in human lung. These models always require information about the parameters of activity size distributions of radon progeny. In the present work, the attached and unattached activity size distribution of 222Rn progeny (214Bi and 214Po) were measured in indoor air of Minia University, Minia, Egypt. The attached fraction was collected using a low-pressure Berner cascade-impactor technique. A constructed wire screen diffusion battery was used for collecting the unattached fraction. Most of the attached activities for 214Bi progeny were associated with the aerosol particles of the accumulation mode. The AMAD of this mode for 214Bi was determined to be 350 nm with GSD of 3. The GSD of unattached size distributions for 214Po is 1.29 with AMTD of 1.25 nm. An analytical method has been developed to compute the local energy deposition of 214Po alpha particles in a target volume of 1 m spheres located at different depths in bronchial epithelium. In order to reach the target, alpha particles travel either through tissue alone or through air and tissue. While the depth-dose distributions in the case of nuclides uniformly distributed within the epithelium were practically constant with depth, they decreased in an almost linear fashion with increasing depth in the case of nuclides on the airway surface.