In this work the lipophilicity of different selenium species occurring in environmental matrices and food, Se(IV), Se(VI), selenomethionine (Se-Met), selenocystamine (Se-CM), selenocystine (Se-Cyst), and dimethyl diselenide (CH3)2Se2, was investigated in the octanol-water system, using the shaking flask method and detection with inductively coupled plasma-atomic emission spectrometry (ICP-AES), in order to assess their environmental fate and tendency to bioaccumulate. Polarography was also used for the electrochemically active Se species, Se(IV), Se-Cyst, Se-CM and (CH3)2Se2, and the results were compared with those measured by ICP-AES. Furthermore, the influence of pH was studied by determining the logarithm of the distribution coefficient, log D, at three pH values, 5, 7, and 9, as was the impact of the marine environment on the lipophilicity profile of the six investigated Se species. The results were compared with those estimated approximately by use of PrologD software, based on the Ghose-Crippen log P (P: partition coefficient) calculation system, the only system which incorporates values-even though approximate-for the atom type of Se. Finally, from our experimental data an indicative value of the Se-Se fragment for log P prediction, for use in drug design, was estimated.