In a study of 25 Tursiops truncatus and two Globicephala macrorhynchus examined by necropsy, abundant HgSe was found in both the liver and in the respiratory system (lung and hilar lymph nodes). In the liver HgSe was consistently associated with the cell-breakdown pigment lipofuscin, whereas in lung and hilar lymph nodes it was consistently associated with particulates consisting of partially graphitic soot and silicates. This supports earlier suggestions that in the liver HgSe may be a storage end product of Hg metabolism, while adding the new suggestion that in the respiratory system HgSe may be inhaled, preformed in combustion emissions.