A deterministic aerosol deposition model, previously validated by data from adult inhalation exposure experiments, is used to study factors affecting particle behavior within the developing human lung. Here, an age dependent lung morphology is presented in which the number of tracheobronchial (TB) generations is complete at birth, but airway dimensions vary with age; the number of pulmonary (P) generations, however, changes with age, as well as alveolated airway dimensions. For the light and heavy respiratory activity levels considered, TB, P and total lung deposition fractions are calculated. For all particle sizes (0.2 - 9.0 micro m) tested, total deposition was minimum for the 30 year old adult and maximum for either of the youngest two subjects (7 and 22 months old). The model is intended to aid in future extrapolation, or age dependent, modeling efforts assessing the threat to human health from airborne contaminants. (Copyright (c) 1989 Health Physics Society, Pergamon Press plc.)