[en] The organ concentration, excretion and excreted forms of selenium were studied in young and adult rats after a single subcutaneous injection of a sublethal dose of ⁷⁵Se-selenite. In the young, about a 10-fold higher concentration of ⁷⁵Se in the blood, liver kidneys and heart was found at all the experimental intervals studied (1 to 7 days). The highest ⁷⁵Se concentration in the young was in the liver while in the adults it was found in the kidneys. The spectrum of radioselenium metabolites in the urine was similar in both groups. However, the main product excreted by young rats was ⁷⁵Se-glutathione selenotrisulfide and an unidentified neutral substance while it was the trimethylselenonium ion in the adults. Ontogenetic differences in the selenium metabolism could be one of the factors underlying the differences in the response of the young and the adult rats to toxic doses of selenite. (author). 2 tabs., 9 refs