Previous research has reported that the lung development of animals exposed to oxidant gases early in life might be impaired, or that developing lungs might be more susceptible than adult lungs to inhaled toxicants. Dr. Mauderly and colleagues at the Lovelace Biomedical and Environmental Research Institute examined the age-related differences in the physiological responses of rats to inhaled automotive emissions. The younger group was exposed during gestation and through the age of six months, while the older group was exposed between the age of six and twelve months. Rats were exposed seven hours per day, five days a week, for six months to 9.5 ppm of NO2, to dilute diesel exhaust, or to filtered air as controls. Health effects were evaluated at the end of six months of exposure, and measurements included: respiratory function, pulmonary immune responses, lung clearance, lung morphology, and histopathology.