Dogs, rats, mice, and gerbils were exposed for 6 hours per day, 5 days per week, for periods up to 2 years, to an atmosphere containing a complex mineral oil-base mist at concentrations of 5 and 100 mg/M3. The mass median diameter of the oil droplets was approximately that found in textile plants ( approximately 1.0 mu). In addition, these test atmospheres contained 1000 ppm acetone,an acetate fiber solvent, in order to simulate fiber plant conditions. Evidence of oil mist was detectable within lung macrophages of all species tested and at both concentrations. Only at the higher concentration (100 mg/M3),, in dogs and rats, but not in mice and gerbils, was a retention of oil of such a magnitude so as to result in the development of oil microgranulomas. Rats given a 10-month recovery period following 12 months of exposure did not completely recover from the oil microgranuloma. These results indicate that the presence of typical textile fiber adjuvants in mineral oil and the concurrent presence of 1000 ppm acetone in the atmosphere do not significantly alter the inhalation toxicity of pure white mineral oil mist.