Subchronic 90-day feeding studies were conducted on four highly refined white mineral oils to determine any potential for toxicity in Long-Evans rats (20 per sex per dose level) and beagle dogs (4 per sex per dose level). Each oil was fed at dietary dose levels of 300 ppm and 1500 ppm (w/w). No treatment-related effects of toxicological importance were detected in daily observations of general health or in periodic assessments of food consumption and body weight, hematology, serum clinical chemistry, and urinalysis. Observations in dogs suggested that the white oils produced mild laxative effects. Gross and histopathologic examinations, as well as measurements of organ weights, did not reveal any macroscopic or microscopic changes which could be due to treatment. In addition, special staining by Oil Red O of liver, mesenteric lymph nodes, spleen, gastrointestinal tract, stomach, and kidneys indicated no evidence of oil or lipid deposition. A special re-examination of tissues from female and male rats, in response to more recent conflicting data from the Fischer 344 strain, found no histopathologic signs of macrophage accumulation and/or microgranuloma formation in liver, spleen, or mesenteric lymph nodes. These data indicate that repeated exposure to relatively high levels of white mineral oils in the diets does not produce significant subchronic toxicity in Long-Evans rats or beagle dogs.