The metabolism of C(14)-d-alpha-tocopheryl quinone (alpha-TQ) and its hydroquinone (alphaTHQ) was investigated. Forty-six hours after intraperitoneal administration of either compound to rats the radioactivity isolated from the liver was present almost exclusively in C(14)-alpha-TQ. The results indicated, however, that in situ this compound was present primarily in the reduced form. No conversion to C(14)-alpha-tocopherol or other liver metabolites was observed. alpha-THQ was eliminated from the tissues more rapidly than alpha-TQ. The main metabolite excreted in the urine was a conjugate of alpha-tocopheronic acid and the main metabolite excreted in the feces was a conjugate of alpha-TQ. Free C(14)-alpha-TQ was present in the feces after administration of this compound but not after C(14)-alpha-THQ administration.