The pneumoconiotic potential of carborundum (409212) was studied in sheep to evaluate the biological activity of mineral dusts found in the carborundum manufacturing industry. Sheep were administered 0 or 100 milligrams latex beads, graphite (7782425), raw or ashed carborundum particles, minusil-5 (7631869) (silica), crocidolite (12001284) fibers, or raw or ashed carborundum fibers, intratracheally. Bronchoalveolar lavage (BAL) was performed 2, 4, 6, or 8 months after exposure to determine total BAL fluid total and differential cellularity. The BAL fluid was assayed for glycosaminoglycan and fibronectin content and lactate-dehydrogenase (LDH) and fibroblast growth activity (FGA), which were used as biological indicators of alveolitis. The sheep were killed at 8 months post exposure and the lungs were examined for histopathological changes. BAL fluid from all particulate dosed sheep revealed an early slight transient increase in total cellularity, except those administered silica. Silica induced a 500% increase in BAL fluid cellularity, due primarily to an increase in alveolar macrophages, at 2 months which was still 250% above the control value after 8 months. Only silica particles caused significant increases in BAL fluid LDH, fibronectin, glycosaminoglycan, and FGA. Lung tissue from graphite and carborundum dosed sheep contained particulate accumulations in the alveoli and interstitium without a cellular reaction. Silica induced a diffuse alveolitis with early nodular silicotic lesions. Crocidolite and raw and ashed carborundum fibers increased BAL fluid total cellularity, LDH, fibronectin, and FGA. The effects were more pronounced in sheep dosed with crocidolite and raw carborundum fibers. Crocidolite induced peribronchiolar fibrosing alveolitis. Nodular lesions were seen in the lungs of sheep administered raw and ashed carborundum fibers. The lesions contained multinucleated macrophages, monocytes, neutrophils, and carborundum fibers and bodies. The response induced by ashed fibers was less severe than those induced by raw fibers.