Nasal inhalation helps to protect the lungs from detrimental effects of toxic particles which, however, may also place the nasal and adjacent tissues at risk. Alternatively, drug-aerosol deposition on pre-determined nasal airway surfaces can be a modern pathway for rapid medical treatment. The present study focuses on inertial particles in the range of 1 mu m <= d(p) < 50 mu m, subject to steady laminar flow rates of 7.5 and 20 L/min. In contrast to ultrafine particles, for certain fine particle sizes deposition is strongly affected by wall roughness, which was incorporated with a selective micro-size airway-surface layer. The validated computer simulation results show that the inertial particle deposition in human nasal cavities increases with increasing impaction parameter, IP = d(a)(2) . Q. Most of the deposition occurs in the anterior part of the human nasal cavities, especially in the nasal valve region. Considering drug-aerosol targeting, an optimal impaction parameter value exists which generates for normal inlet conditions the largest deposition in desired areas, e.g., the middle meatus, inferior meatus and olfactory regions. However, the absolute deposition efficiencies, especially in the inferior meatus and olfactory region, are very small because particles hardly reach those regions due to the complex nasal geometric structures. The influence of gravity was also analyzed and an experimentally validated correlation for inertial particle deposition in human nasal cavities has been provided. (c) 2007 Elsevier Ltd. All rights reserved.