The metabolism of tetraphenyltin in rat liver and kidney has been examined. Tetraphenyltin and its metabolites in the tissue were determined periodically for 96 h after a single oral dose of 55.4 mg kg(-1) of tetraphenyltin by gas chromatography. The gas chromatographic method was able to determine simultaneously both inorganic tin and phenyltin compounds. Although initial (at 24 h) levels of tetraphenyltin in the liver approximated four times those in the kidneys, the levels of tetraphenyltin decreased more rapidly with time than those in the kidneys. These findings show that the tetraphenyltin accumulated more rapidly and highly in the liver, but was metabolized faster than that in the kidney. The levels of total tin in the liver 24 h after treatment were distinctly lower than those of di- or triphenyltin treatments in our previous studies and none of the animals showed characteristic symptoms. The toxic potencies of organotins generally correlate with accumulation of the chemicals. These results imply that the slight toxicities of tetraphenyltin might be due to the relatively low uptake of tin compounds after ingestion. The highest tin concentration among the metabolites of tetraphenyltin in the tissue, especially in liver, was observed as diphenyltin throughout the time period studied. These results suggest that part of the administered tetraphenyltin may cause some harmful effects as diphenyltin in rats, and this must be taken into consideration in toxicological research on tetraphenyltin.