Summary A 17.5-fold increase of carrier SeO4 did not alter the urinary excretion of 75Se, increased its respiratory excretion and hepatic uptake, but decreased its uptake in other viscera. 75Se accumulation in the liver and pancreas was similar after 75Se-methionine and after 75SeO4 injections. After CCl4 therapy urinary excretion, and renal and pulmonary uptake of 75Se increased. In choline deficient cirrhotic rats urinary excretion of 75Se decreased and visceral, though not the hepatic, uptake of 75Se increased. However, SeO4 supplements reversed these changes in the cirrhotic rats with the exception of the increased renal uptake of 75Se. Over 80% of the non-dialyzable 75Se in the liver accumulated in the mitochondrial and supernatant fractions. The increase of carrier SeO4 was accompanied by an increase of 75Se in the nuclear fraction but did not change the distribution of 75Se in the mitochondrial, microsomal and supernatant fractions. The 75Se uptake increased in the nuclear fraction after CCl4 therapy and in choline deficiency induced cirrhosis. SeO4 supplements did not alter this increased uptake.