Introduction. Morphometric model. Physiological parameters. Radiation biology considerations. Deposition model. Gases and vapours. Clearance model. Dosimetry. Application of the model. Summary description of respiratory tract dosimetry model. References. Annexe A - Anatomy and morphology of the respiratory tract. Annexe B - Respiratory physiology. Annexe C - Effects of radiation on the respiratory tract. Annexe D - Deposition of inhaled particles. Annexe E - Clearance of particles from the respiratory tract. Annexe F - Reference values for regional deposition. Annexe G - Specific absorbed fractions of photon energy. Annexe H - Absorbed fractions for alpha, beta, positron, and electron emissions.