In vitro studies suggest that reactive oxygen species contribute to the cardiopulmonary toxicity of particulate air pollution. To evaluate the ability of particulate air pollution to promote oxidative stress and tissue damage in vivo, we studied a rat model of short-term exposure to concentrated ambient particles (CAPs). We exposed adult Sprague-Dawley rats to either CAPs aerosols (group 1; average CAPs mass concentration, 300 +/- 60 micro g/m3) or filtered air (sham controls) for periods of 1-5 hr. Rats breathing CAPs aerosols for 5 hr showed significant oxidative stress, determined as in situ chemiluminescence in the lung [group 1, 41 +/- 4; sham, 24 +/- 1 counts per second (cps)/cm2] and heart (group 1, 45 +/- 4; sham, 24 +/- 2 cps/cm2) but not liver (group 1, 10 +/- 3; sham, 13 +/- 3 cps/cm2). Increases in oxidant levels were also triggered by highly toxic residual oil fly ash particles (lung chemiluminescence, 90 +/- 10 cps/cm2; heart chemiluminescence, 50 +/- 3 cps/cm2) but not by particle-free air or by inert carbon black aerosols (control particles). Increases in chemiluminescence showed strong associations with the CAPs content of iron, manganese, copper, and zinc in the lung and with Fe, aluminum, silicon, and titanium in the heart. The oxidant stress imposed by 5-hr exposure to CAPs was associated with slight but significant increases in the lung and heart water content (approximately 5% in both tissues, p < 0.05) and with increased serum levels of lactate dehydrogenase (approximately 80%), indicating mild damage to both tissues. Strikingly, CAPs inhalation also led to tissue-specific increases in the activities of the antioxidant enzymes superoxide dismutase and catalase, suggesting that episodes of increased particulate air pollution not only have potential for oxidant injurious effects but may also trigger adaptive responses.