A comparison of the concentration-response effects of inhaled ozone (O3) in different species of laboratory animals was made in order to better understand the influence of the choice of species in inhalation studies of this gas. The effect of 4 hour exposure to ozone (O3) at concentrations of 0.0, 0.2, 0.5, 1.0, and 2.0 ppm was determined in rabbits, guinea pigs, rats, hamsters and mice. Lavage fluid protein (LFP) accumulation 18 hr after exposure was used as the indicator of 03-induced pulmonary edema. All species had similar basal levels of LFP (250-350 ug/ml) when a volume of saline which approximated the total lung capacity was used for lavage of the collapsed lungs. Exponential dose-response curves were seen in all species except guinea pigs, which showed significant increases in LFP at low 03 concentrations (0.2 ppm) and a leveling off of response at the higher 03 levels. Other species usually showed significant elevations in LFP only at concentrations greater than 0.5 ppm. Recovery of lavage fluid as a percent of the amount of injected saline varied significantly between species, and between 03 concentrations; higher 03 levels causing lower recovery. The time course of LFP accumulation also appeared to vary according to the species.