Inhaled particle deposition sites must be identified to effectively treat human airway diseases. The authors have determined distribution patterns of a selected aeroallergen, ragweed pollen, among human extrathoracic (ET: i.e., oro-nasopharyngeal) regions and the lung. A predictive model validated by inhalation exposure data from human subjects was utilized. Deposition locations were primarily functions of (1) ragweed particle parameters (size, 14-20 micrometers; shape, spherical; and density, 1.14 g cu cm) and (2) mode of breathing. In the general population, two styles of inhalation are prevalent: normal augmentors (NAs), and mouth breathers (MBs), their clinical definitions are based on intra-ET airflow divisions. For a NA-mode breathing, sedentary (10 L/min) adult, 88% of inhaled ragweed pollen was removed by the ET compartment and 7.0% collected within the lung. For a MB, the respective deposition efficiencies were 68% and 25%. To apply the model, they used a daily springtime ragweed pollen concentration of 300 grains/cu m and an exposure time of 0.5 hour to calculate actual doses for the respiratory system. Under the stipulated conditions, a MB would inhale 45 pollen grains per day and 8 would be deposited in the lung; the value is 3 grains for a NA. Frequently, individuals with impaired respiratory functions are MBs in whom such pollen deposits are likely contributors to airway disease.