The lipophilicity of the anionic forms of drugs and model compounds was assessed by their transfer across (i) the water-2-nitrophenyloctyl ether (NPOE), (ii) the water-nitrobenzene (NB), and (iii) the water-n-octanol interfaces by using the three-phase electrode technique. The lipophilicities, expressed in terms of logarithm of partition coefficients, range for the studied anions from -3.46 to 0.68 (log P-A-,aq(circle minusNPOE)) for NPOE, from -3.81 to 2.62 (log P-A-,aq(circle minusNB)) for NB, and from -6.20 to -3.20 (log P-A-,aq(circle minusn-oct)) for n-octanol. Although NPOE shares with nitrobenzene the aromatic part and with n-octanol the hydrophobic carbon chain, only very weak correlation was observed between the NPOE-based-data with the n-octanol-based data, and the same is true for the correlation of the NB-based and n-octanol-based data. However, there is a strong and even linear correlation between the NPOE-based and the NB-based data.