Subchronic inhalation studies were performed with three petroleum lubricants: generic cutting oil (GCO), generic gear oil (GO), and generic commercial engine oil (CEO). Each formulation had a mineral oil base. Sprague-Dawley rats were exposed 6 hours/day, 5 days/week for 13 weeks to aerosol concentrations of 0 (untreated controls), 0 (sham-exposed controls), approximately 50, 150, or 400-520 mg/m3. At necropsy, 15 rats/sex/group were sampled for serum chemistry (18 parameters), hematology, and weights of 13 organs. Testis and epididymis of males in the control and high-dose group were used for number of spermatids and morphology of epididymal sperm. Histopathological slides were evaluated for 22 or more organs. Pulmonary function tests were done on 10 additional males/group. Pulmonary hydroxyproline was measured in these rats for GCO and GO. Residual oil in the lungs was determined for GCO. The primary organ affected by exposures to these three formulations was the lung; the main observed effects were accumulation of foamy macrophages in pulmonary alveoli and alveolar walls, very mild thickening of alveolar walls due to foamy macrophages and a mixed cell infiltrate, and subtle epithelial hyperplasia. The foamy macrophages tended to group together in aggregates, and the aggregates seemed responsible for plaques seen visibly on the surface of the lung. These histological changes were accompanied by concentration-related increases in lung weight and pulmonary hydroxyproline, whereas pulmonary function tests were generally unaffected. Effects distal to the lung were more limited. These results indicated low toxicity of these aerosols in this model.