[en] Artificial radionuclides are released into the aquatic environment. Some of them are incorporated into aquatic organisms. An attempt has been made to elucidate the accumulation of radionuclides within the intracellular constituents of these organisms. On chronically radiolabelled animals (labelled sea water), the subcellular localisation of ²⁴¹Am in the digestive gland cells of periwinkles and of oysters was determined. Similar experiments were performed on the hepatopancreas of the lobster (labelled food) with ²⁴¹Am, ²³⁸Pu and ⁹⁵Tc^m, and in pyloric caeca of sea-stars with ²⁴¹Am, ²⁵²Cf and ⁹⁵Tc^m. The distribution of ¹³⁷Cs was studied in cytosolic fractions of muscle and liver of eels and in the oyster. Distribution of radioelements appeared to correlate with the metabolic pathways of the species studied and with the chemical nature of the radionuclide. The results provide data in radioprotection research and may explain the biokinetics which were observed for whole organisms. (author)