The authors compared the temporal pattern of low-dose oxidant-induced lung injury in rats after exposure to either 1 ppm ozone or 100% oxygen for 24 hI' or from treatment wi.th paraquat (20 mg/kg, l.ntraperitoneally). Histological abnormalities in airways, parenchyma, and blood vessels were evaluated from coded and randomized sections and compared with appropriate controls. Drug metabolism by lung endoplasmic reticulum was studied in similarly treated rats as another index of Rung injury. Exposure to oxygen caused no discernible morphologic or biochemical abnormalities. Exposure to ozone caused hlsto logical lesions which appeared early and resolved by 7 to 14 days, whereas paraquat-induced lesions were first evident at about 7 to 14 days. Abnormalities in drug metabolism followed a similar pattern. Low-dose oxidant exposure from ozone and paraquat produce similar histological and biochemical lesions in rat lungs but with distinct temporal patterns.