Butylated hydroxyanisole (I) is one of the most commonly used food antioxidants. Its use has been suggested to inhibit a variety of carcinogenic responses. The present study on the disposition kinetics of (I) in man indicates that contrary to previous reports, (I) undergoes significant O-demethylation in the body yielding a tert-butyl hydroquinone. It is suggested that this metabolic conversion may be responsible for some of the in vivo activities of (I) against chemical carcinogens.