AbstractButylated hydroxyanisole and butylated hydroxytoluene are used extensively as food antioxidants. It is estimated that man consumes ca. 0.1 mg/kg body wt daily of these antioxidants. At levels 500 times this level (50 mg/kg/day), both butylated hydroxyanisole and butylated hydroxytoluene appear to be free of any obviously injurious effects. However, at larger doses (500 mg/kg/day), both butylated hydroxyanisole and butylated hydroxytoluene result in certain pathological, enzyme, and lipid alterations in both rodents and monkeys, and butylated hydroxytoluene, in some cases, has been reported to have certain teratogenic and carcinogenic effects upon rodents. These alterations appear to differ markedly between rodents and monkeys, apparently as a result of differences which exist in the metabolism and excretion of butylated hydroxyanisole and butylated hydroxytoluene by these two species. However, in both animal species, the alterations appear to be physiological responses which are reversible upon removal of butylated hydroxyanisole and butylated hydroxytoluene from the diet. Long term chronic ingestion of butylated hydroxyanisole and butylated hydroxytoluene may be beneficial in sparing vitamin E and in modifying the acute toxicity of a number of mutagenic and carcinogenic chemicals.