Abstract The effects of the food antioxidants butylated hydroxyanisole (BHA) and butylated hydroxytoluene (BHT) on renal function were studied. Male rats were given 500 mg BHA or BHT/kg/day by gavage for 6 days. Control animals received corn oil alone. Animals were offered a grain diet and distilled water ab lib. Water and food intakes, and urinary volume, osmolality, and sodium and potassium concentrations were monitored daily for each animal. Following the second dose BHT, the urine volume of treated animals was increased by 78% while water intake was reduced 35%. No discrepancies occurred in the fluid balances of BHA-treated or control animals. The osmolality of urine from animals receiving BHT was reduced for the 6 days of the experiment; that of BHA and control groups was unaffected. Urinary sodium and potassium concentrations were reduced in animals treated with either antioxidant. On the second day of BHT administration, excretion of electrolytes was reduced, but not in proportion to food intake. This may have been related to hormonal changes accompanying the depression of food intake. Total daily sodium excretion of BHA-treated animals was less than expected from food intake on days 2–6, possibly owing to interference with renal prostaglandin synthesis.