The effect of freshly fractured quartz produced in sandblasting, rock drilling, tunneling, and silica flour milling operations on enhanced acute lung injury in rats was investigated. Three study groups of 20 male Fischer-344-rats were exposed to freshly fractured quartz (14808607) dust, aged quartz dust (for 60 days), or fresh air for 5 hours a day for 10 days. The mean quartz dust concentration in the exposure chamber was 20mg/m3. At 48 hours postexposure, animals were sacrificed for histopathologic examination and bronchoalveolar lavage. Lavage cells were analyzed to determine activity and release of lactate-dehydrogenase, N-acetyl-beta-D-glucosaminidase, catalase, superoxide-dismutase, and glutathione-peroxidase. Measurement of oxygen radicals produced during phagocytosis was performed by spin trapping and spectrophotometry. Lipid peroxidation and bronchoalveolar lavage fluid changes were also assessed. Rats exposed to both freshly fractured and aged quartz dust exhibited increased numbers of bronchoalveolar lavage cells, pulmonary infiltration, lung injury, increased lipid peroxidation, and oxygen radical production by pulmonary phagocytes. These symptoms were more pronounced in the group exposed to freshly fractured quartz dust. The authors conclude that freshly fractured quartz may be associated with inflammation and lipid peroxidation responses that could result in acute silicosis.