Recent epidemiologic studies suggest increased mortality among the elderly in association with particulate air pollution. We investigated the variability in fractional deposition (DF) of inhaled particles (2 microns mass median aerodynamic diameter [MMAD]) in 62 subjects with normal lung function, aged 18 to 80 yr. Each subject inhaled 2-microns monodisperse carnauba wax particles while following a breathing pattern previously determined by respiratory inductance plethysmography in that subject (i.e., particles inhaled) was determined by laser aerosol photometry and pneumotachometry at the mouth. DF (mean DF = 0.29 +/- 0.06 (ages 18 to 40 yr), 0.29 +/- 0.07 (ages 41 to 60 yr), and 0.26 +/- 0.06 (age over 60 yr) was independent of age. There was a tendency toward greater DF in female than in male subjects; DF = 0.30 +/- 0.07 (females) and 0.27 +/- 0.06 (males) (p = 0.06); however, because the males had 45% higher minute ventilations than the females, the deposition rate (Drate), or particles depositing per unit of time, was 30% greater in males than in females (p = 0.004). Multiple regression analysis showed that among all subjects, the variability in DF was best predicted by variability in the breathing period (T) associated with the pattern used to breathe the particles, and by the subject's specific airway resistance (sRAW). These results may prove useful in determining age- and gender-relative risks that may be associated with the inhalation of pollutant particles in ambient air.