Experimental determination of ozone (O3) uptake in the conducting airways and lungs is a fundamental starting point for interspecies comparisons of delivered dose. Fractional O3 uptake was measured in the respiratory tract of awake Fischer 344 rats and in the lungs and nasopharynx of young healthy male humans. Awake animals were individually evaluated during nose only exposures to 0.3 ppm O3 for O3 removal, O2 consumption, CO2 production and tidal breathing while inside a body plethysmograph. Utilizing these values of O3 uptake and measures of ventilation, the mass dose rate of O3 per unit respiratory tract surface area was computed and found to be similar between rats and humans for the same ambient O3 concentration.